# My progress in building a wood fired boiler based on the design by Richard C. Hill



## Hobartian

I am currently building a wood fired boiler based on the design by Richard C Hill for a Stick-Wood Fired furnace.

I am about a month away from completion.     My efforts can be viewed on the following link:

https://sites.google.com/site/mywoodfiredhydronicboiler/my-construction-of-a-wood-fired-boiler

I will be making frequent additions to the web site.

Regards


----------



## jimbom

This is interesting to me.  Thanks for sharing.  Tasmania must get a few shots of cold from the great south ocean.  Better hurry if this is to help this winter.


----------



## kuribo

I am thinking of making my own boiler as well, but out of fire brick with a fire tube heat exchanger in the exhaust path. Was wondering if you could share any design/build details of your fire tube heat exchanger?


----------



## hedge wood

Your burn chamber looks a lot like the secondary burn chamber in a Garn. Is this your only burn chamber. Can't wait to see the rest of the build.


----------



## Gasifier

Very interesting. Keep us posted. I would like to follow your progress and hope it works well for you. Best of luck with it. About how many BTUs will it throw when completed?


----------



## Hobartian

kuribo said:
			
		

> I am thinking of making my own boiler as well, but out of fire brick with a fire tube heat exchanger in the exhaust path. Was wondering if you could share any design/build details of your fire tube heat exchanger?



I used a discarded propane cylinder which is approximately one hundred centimeters long and about thirty eight centimeters in diameter.   I removed the handles from the top of the cylinder and the steel welded onto the base.    I then drilled twelve forty millimeter holes around the perimeter of each end of the cylinder and welded forty millimeter steel pipe from a hole in one end to the corresponding hole in the other end.    Please note that holes will be on a curved part of the cylinder ends. 

 I then made a sleeve to fit around the cylinder at the exhaust end so that I can collect the exhaust gases for discharge through the chimney.

I am hoping this will be satisfactory as the heat exchanger will be operating on a very low pressure.


----------



## Hobartian

Gasifier said:
			
		

> Very interesting. Keep us posted. I would like to follow your progress and hope it works well for you. Best of luck with it. About how many BTUs will it throw when completed?



Professor Hill quoted the figure of about one hundred thousand btu's per hour and that was with a bare minimum of insulation.     He also quoted the figure of eight pounds of wood being burnt per hour.    That capacity to generate heat will be more than enough for my needs.   I will be storing heat in a one thousand three hundred liter insulated tank.   (340 gallons)


----------



## Donl

Hobartian said:
			
		

> Professor Hill quoted the figure of about one hundred thousand btu's per hour and that was with a bare minimum of insulation.     He also quoted the figure of eight pounds of wood being burnt per hour.



One pound of wood will produce about 8000 btu's. therfore eight pounds will produce a maximum of approx 64000 btu's if 100% efficient.


----------



## Hobartian

Thanks for your comments and interest which I appreciate.

I couldn't argue with anyone about the actual heat capacity of the boiler at this point of time particularly as I am not strictly following Professor Hill's design.   My heat exchanger is much larger and the storage tank will be mounted directly above the heat exchanger with two huge connections.

I am certainly looking forward to firing it and starting trials on how I can get the best performance out of it.   In this regard Professor Hill did a lot of experimentation and provides information about different things that he tried that worked and others that were not successful.    From a commercial point of view my boiler is very large and lacks portability but this is not a problem for me.

I am certainly hoping the boiler works better that my first two attempts to create the hot water I need.  Initially I built a large refrigerated heat pump to extract heat from a water tank under my house.   Whilst it produced some heat it wasn't nearly enough.   I then tried adding to the heat by installing a three meter stainless steel coil into a slow combustion heater which I completely insulated so that the coil was the only means to take heat away.   That worked a little but quickly became ineffective when the coil was covered with a thick layer of creosote.   I have no doubt that a very small coil would work if it was used only to heat the domestic hot water supply.


----------



## jimbom

:long: It seems when we couple the heat source with the storage source using water, we always get creosote formation.  We need to couple the fire box to the storage box with a fluid that is not limited to 212 Â°F boiling if we don't want a pressurized system.  Something safe, cheap, commonly available, and able to absorb, carry, and discharge the energy.  Air?  Low specific heat and high pumping cost :shut: .  But  , maybe air.  Especially if the load was low and the storage side heat exchanger had a high surface area.  Air!  Eureka. Runs naked in the woods :ahhh: .


----------



## Hobartian

JimboM said:
			
		

> :long: It seems when we couple the heat source with the storage source using water, we always get creosote formation.  We need to couple the fire box to the storage box with a fluid that is not limited to 212 Â°F boiling if we don't want a pressurized system.  Something safe, cheap, commonly available, and able to absorb, carry, and discharge the energy.  Air?  Low specific heat and high pumping cost :shut: .  But  , maybe air.  Especially if the load was low and the storage side heat exchanger had a high surface area.  Air!  Eureka. Runs naked in the woods :ahhh: .



I will find out soon whether I am going to create any creosote but Professor Hill in his report said that his boiler did not have any deposits of creosote.    I don't think water is the problem.  I am more inclined to think trying to burn timber at too low a temperature is the problem.  If the heat exchanger is in the firebox or in very close vicinity,  the fire is robbed of it's heat.   However, if you maintain a high burn temperature and completely burn all the gases before they reach the heat exchanger there would be nothing left to deposit  there.  This is the basis of Professor Hill's design.

To add further argument to the point that water is not the problem there are multitudes of homes with creosote laden chimneys created by wood heaters and not a drop of water in sight.   In these cases the creosote is created because of smoldering oxygen starved fires, damp timber, etc.

Another element of Professor Hill's design is the forced input of high velocity air which is introduced into the burn chamber so as to cause create turbulence.   Professor Hill reported that he tried to eliminate the use of the input fan but when he did so the burning process was severely impeded.

Thanks Professor Hill for your detailed report.


----------



## jimbom

Hope you are correct.  I would like to see your stove succeed.  Besides, this running naked in the woods is not all it is cracked up to be.


----------



## webbie

Wet wood can be burned cleanly...of course, but there is no getting around that a lot of the energy in the wood will be lost. 

Also, although wood contains 8-9000 BTU per pound, once it is adjusted for moisture and efficiency it turns out that about 5K BTU is the highest output you can get from it. That would mean 8 lbs of wood per hour would produce approx. 40,000 BTU per hour.


----------



## Hobartian

I have just been reading the patent application for the Wood Stick Furnace designed by Richard C. Hill. 

 The figures I quoted in my earlier post appear not to be correct as it is stated in the application that a sixteen inch diameter combustion chamber with a height of three to four feet can be loaded with forty pounds of wood which will burn at the rate of twenty pounds per hour and thus create 100,000 BTU per hour.

My storage capacity is one thousand three hundred liters which should be heated in less than two hours.   Of course time will tell and I will report on the actual performance in due course.


----------



## kuribo

Hobartian said:
			
		

> kuribo said:
> 
> 
> 
> 
> I am thinking of making my own boiler as well, but out of fire brick with a fire tube heat exchanger in the exhaust path. Was wondering if you could share any design/build details of your fire tube heat exchanger?
> 
> 
> 
> 
> I used a discarded propane cylinder which is approximately one hundred centimeters long and about thirty eight centimeters in diameter.   I removed the handles from the top of the cylinder and the steel welded onto the base.    I then drilled twelve forty millimeter holes around the perimeter of each end of the cylinder and welded forty millimeter steel pipe from a hole in one end to the corresponding hole in the other end.    Please note that holes will be on a curved part of the cylinder ends.
> 
> I then made a sleeve to fit around the cylinder at the exhaust end so that I can collect the exhaust gases for discharge through the chimney.
> 
> I am hoping this will be satisfactory as the heat exchanger will be operating on a very low pressure.
Click to expand...



How in the world did you drill clean holes through a curved surface and keep the holes in the top and bottom aligned?

How many firetubes are you using? Thanks again....


----------



## Hobartian

Hi Kuribo,

(How in the world did you drill clean holes through a curved surface and keep the holes in the top and bottom aligned?
How many firetubes are you using?)

It wasn't difficult as due to the length of the cylinder there is quite a lot of tolerance to align the holes.    What I did was use the seam along the length of the cylinder as a starting point and marked out the holes.   I then drilled the holes at each end which I filed to an elliptical shape to allow the tubes to be inserted and run parallel to the sides of the cylinder. 

I have used twelve fire tubes but this is probably more than is needed particularly as the tubes are much longer than in Professor Hill's design


----------



## jebatty

I've used 6050 btu/lb available heat energy of wood at 20% MC and 400F stack temperature. My Tarm burns a little hotter than 400F stack, ranging about 380-480F over the course of a burn. In doing this I have calculated 83% efficiency for my Tarm. If stack temperature was constant 400F, the efficiency would be about 85-86%.

I believe this is pretty good based on 1) weighing the wood, including kindling; 2) firing the boiler at a cold start; 3) mixing the 1000 gal storage tank to a uniform temperature before starting the burn; 4) mixing the storage tank to a uniform temperature at the end of the burn; 5) adding 55 gallons of water to account for the boiler; 6) calculating the btuâ€™s based on the deltaT in the tank+boiler from beginning to end of burn; and 7) not drawing heat from the system during the burns.

The "variable" in this calculation is actual MC of the wood. My wood is 2-year air dried but stored outside with a cover to shield from rain/snow, so I also think 20% MC is pretty close. Btu/lb would go up as MC goes down, and vice versa.


----------



## Hobartian

I am including a rough drawing of the boiler.

 Steady progress is being made with the assembly and I hope to begin testing soon.


----------



## jimbom

Excellent.  I can't wait to see the results.


----------



## thecontrolguy

Hobartian;

I am VERY intrigued and interested in your design / build.  Bravo!! Firstly, I hope it works really well, and perhaps better than you are hoping for.  I am also hoping that you are able to provide this forum with more detailed drawings (with dimensions) and more pictures to illustrate some of the details of your interpretation of this Hill Design.  Also, I am curious as to what materials (steel wise) were used, especially for the fire tubes, and, of course, the rod used to weld them in to the old propane cylinder.  Are the vertical connections from the heat exchanger to the heat storage tanks fabricated, and if so, from what? I am wondering here why you wouldn't used pipe sections? AND, how are you getting ash out of the fire box?  As usual, any and all information is very much appreciated.   Cheers!


----------



## Hobartian

Response to The Control Guy

My Google site has a lot of pictures and I will keep updating it.  This is the link.

https://sites.google.com/site/mywoodfiredhydronicboiler/my-construction-of-a-wood-fired-boiler

The boiler tubes are mild steel.    I used square mild steel tube to connect from the heat exchanger to the tank because I had it on hand and also it is much easier to cut square holes than round ones.   All welding has been done with mild steel rods using either a stick welder or tig although some joints I have silver soldered.   

How to get  the ash out of the burn chamber?   Good question!   My understanding is that there will be very little ash to remove because at such high temperatures everything is consumed.    Apparently I will need to remove some very fine ash from the expansion chamber and there is a hole to access that chamber.    I will probably wait for it to cool down and vacuum the ash out.    This is a matter that I will experiment with and report on in due course.


----------



## Hobartian

I have had a major setback with the construction of the boiler which has caused me to modify the design.

I attempted to connect the heat exchanger tank to the storage tank with two rigid square steel pipes.   However, each time I have tried to pressure test the tanks,  the connecting pipes have failed due to cracking of the silver soldered joints.    I have seriously underestimated the forces involved when you connect two heavy tanks together when there is potential for movement.   

I have now removed the rigid connections and I will be joining the tanks with a two inch stainless steel flexible hose.   I am hoping that the two inch size will be large enough for the heat to equalize between the tanks.

Other parts of the construction are on track and I hope to begin testing soon.


----------



## jimbom

Thanks for the update.  Your project is very interesting to me.  Hope you don't have any more bumps in the road.


----------



## Snail

I am really interested in your project.  I would very much appreciate it if you could post more details on your construction when you have more time, perhaps after you have finished the actual work.

There is one thing that puzzles me about your heat exchanger, as shown on your sketch.  How does the water circulation work?  I would have expected that the pipe exiting the exchanger would need to be taken up to nearer the top of the storage tank in order to get a thermo-siphon working.  There may be some thermo-siphon effect due to the firebox end being warmer than the flue end, but is this enough, especially at start-up?  Also, having both pipes terminating at the bottom of the tank seems to risk a circulation short-cut and consequent overheating of the heat exchanger.

Will you be potting the whole furnace in vermiculite concrete as Dr Hill did?

Thinking about this design, I was wandering how you would adjust the primary and secondary air flow rates to optimum when you cannot see the flame.  Otherwise it seems a really good concept.


----------



## Hobartian

Thanks Snail for your post.

I will be encasing the burn chamber and the secondary chamber with vermiculite cement but that will be done last as once it is done it will be difficult to undo.

You raised the issue of the way I have connected the heat exchanger to the storage tank. 

Originally I intended to do this with two rigid rectangular pipes that each measured about 120mm by 60 mm.   I thought the sheer size of the two pipes combined would be enough for the heat to equalize by convection.    However, this did not work as the movement between the heat exchanger and storage tanks due to expansion and contraction fractured the connecting joints.   Presently I have the tanks joined by a 50mm  stainless steel flexible hose.     I test fired the boiler today using only a small amount of firewood and I observed there was a huge temperature difference between the heat exchanger and the storage tank.    I recorded 88 C in the heat exchanger whilst the water in the tank was only 28 C

I think I will modify the system by installing a 50mm pipe from the top of the heat exchanger to the top of the storage tank.   I will then install a pipe from the bottom of the storage tank to the bottom of the heat exchanger.     That should enable a good thermosiphon loop.

In regard to adjusting the air input that will be a matter for future experimentation.  From my memory of reading Professor Hill's papers,  the design allows the fire to draw the amount of air that it needs.


----------



## Snail

Hey, you got it going!  Fantaastic! My congratulations.

It may not be necessary to further modify the heat exchanger itself.  Probably all you need to do would be to put an extension of one of the pipes inside the tank to near the top.  (It doesn't need to be completely "waterproof")  If that doesn't work you won't have lost anything, since it is a halfway step on the approach that you have suggested.

It's best to  lengthen the pipe from the hot end of the exchanger.  This will make a counter-flow exchanger, which is much more efficient than the reverse.

How are you making the turbulators?  The pdf of Dr Hill's paper doesn't say what his final design was, only that wire bottle-brushes worked but weren't durable.  Not too surprising in an oxygen-rich flame.

I used to work with a guy who did his time on KA steam locomotives.  Pity he is not still around, what a goldmine of info he would be.  His stories were amazing.  He was a big bloke and he still remembered the pain of crawling through a hot firebox to get at the fire tubes.  Those old locos were amazing to see, they were still the mainline passenger express hauler when I was a young man, but the boilers had to be practically re-built after not too many round-trips between Wellington and Auckland.  To minimise down-time, fire-tube replacement began the instant the firebox was dumped.  Ouch!  

I don't know anything about wood-furnace technology, but I imagine that  here too the fire-tubes must burn out eventually.  That would be end-of-life for this design.  Anyone have any info about longevity of the tubes in this environment?


----------



## Hobartian

I have been using the boiler after changing the pipe connections between the heat exchanger and the storage tank.    There is a learning curve involved but I am encouraged with the results I am getting.    

The wood burns with extraordinary ferocity and very little ash is left.   I have heated the water in the 1300 liter storage tank to seventy seven degrees which is high enough for my hydronic heating system.   I have a number of things I want to do to complete the project.   The main job being to insulate the heat exchanger and storage tank.  At this point of time my three car garage is warm from the heat radiating from the device so there is a lot of heat being wasted.

During my test runs I have been using low grade timber and I expect better results when I load the wood chamber with long thick sticks of timber.    It has been raining here in Hobart for the past week  so I have to wait for some fine weather to collect more  firewood.

My progress in building the boiler has been slow and difficult mainly due to the mistakes I have made in the fabrication.  Welding used galvanized cylinders is not easy.  If I was to build the boiler all over again it would be much easier the second time around.     I certainly couldn't recommend building your own boiler to save money particularly if commercial units are locally available.   However,  I have a sense of achievement and satisfied my curiosity.


----------



## Snail

Good to see you have had success after your hard work.  Will you be posting any details?  I would be very interested in any key dimensions.  However the ceramic materials are what really would be helpful down this end of the world.  Prof Hill's paper refers to materials that as far as I can tell are not available at this time and place, so an update on the Australian materials that are suitable could be good.  Also, was there anything special about your clay pots, or are they just run-of-the-mill garden shop variety?


----------



## tom in maine

If you spoke with Dick Hill, he would suggest using firebrick in lieu of castable refractory. It is simple to locate and is
serviceable in inexpensive.

Vermiculite is still available. It is used for potting plants and also for shipping glassware!

Dick is headed to age 93 and is still on the radio every Saturday morning with me.


----------



## Snail

Hi Tom,

A firebrick construction would be very different in shape.  Would the corners and sharp angles not affect the flow and thus performance?  I guess that it would be more difficult to have a firetube setup without at least some castable ceramic in the system?  

The great thing about Dick Hill's paper is that it is so far the only comprehensively tested design that I have been able to find by Googling, that is also reasonably well documented. so that a DIYer can construct it with a reasonable hope that it will work properly.   Do you know of any well-tested an designs in firebrick that are likely to match the efficiency of Dicks original design?

In this neck of the woods, there aren't many second hand furnaces available and the price of efficient new ones is truly frightful.  The market is much too small to get real competition and economies of scale. 

Good to hear that Dick is still going strong.  It gives hope to the rest of us!


----------



## Hobartian

Hi Tom and Snail

I have no doubt good quality fire brick would do the job.    In my case I used cheap unglazed clay pots as form work for the refractory cement. 

  I applied the cement in sections as it it was easier to apply in a horizontal position.   After the cement went off I would turn the pot about ninety degrees and do another section.   As the cement was applied within a couple of days and each section had a good overlap the whole thing has cured into one solid piece.   I used Densecrete 145 which is described at the following link:  http://www.darleyfirebrick.com.au/techcast.html 

Some dimensions are:    The pots were 31 cm high and 51 cm at the widest point.     The burn chamber I created inside the pot is 34 cm wide and 26 cm deep.   The burn tube connected the two pots is 12 cm in diameter and 26 cm long.   The second pot is lined with Litecrete and the chamber diameter is reduced to 34 cm at the exit to allow the heat exchanger to fit nicely.     (I used old propane cylinders for the wood feed tube and heat exchanger which are 34 cm in diameter.)   The wood feed chamber is 78 cm high.

I used the ends of gas cylinders for the lid for the wood feed tube and the end of the heat exchanger.     They work well as the ends seems to be made from thicker steel than the walls of the cylinder.

The main problem I have had is in fabricating the 1300 liter storage tank.   In hind sight I should have followed Professor Hill's example by using very large ready made cylinders which are so much stronger than my square tank.   You need to ensure the piping from the water jacket and the heat exchanger to the storage tank is of large diameter.   I have changed to 1 1/2 inch steel tube with flexible stainless steel hoses inline to cater for movement.

It is a good idea to try and build the whole thing in modules so that you can pull things apart if needed.   I have found that high temperature silicone is good for sealing the joints between components.    Another thing that I have not mentioned is that the pots have developed a number of fine cracks but I am not worried  as the refractory cement inside seems to be solid.

 I bought the forced air pump and exhaust fan through Ebay USA and had them posted to me.    Most parts seem to be much cheaper in the USA than in Australia.


----------



## tom in maine

Using firebrick does not introduce any major issues. The nice thing about firebrick is the cost and the stress relief that is built in since there are 
joints every couple inches. I use a tile saw to cut special sizes and angles that are exact.
I know that we have used firebrick on many prototypes as did Dick back in the day. Castable materials need to be thoroughly cured and are still apt to crack over time. A cracked firebrick is a simple repair.

Building or locating tanks can be a challenge. Maybe that is why we manufacture them. :bug: 

Square tanks want to become cylinders when loaded with water, but most materials lend themselves to building square tanks.
Dick started out using new oil tanks while trying to pressurize them a couple psi. Of course, this did not work very well and this is how we
started working together, since I was building tanks and heat exchangers.

There is some good information on www.builditsolar.com related to building tanks. If heat exchangers are a problem, stainless steel plate heat exchangers can be had for very reasonable prices with the additional cost of another circulator pump.

I think it is hard to consider any other material than smooth copper for coiled hx. When properly designed, they work extremely well and are cost effective. We came up with the initial design concept that we now use, and refined it to the point it is at today. We have been using the basic concepts for about 30 years with very good, long lived results.


----------



## Snail

Hi Tom,

When you recommend a copper-tube heat exchanger, do you mean for a water-to-water exchanger to isolate the furnace circulation water from the remainder of the system, or a furnace gases to water exchanger?  I ask because Hobartian refers to the fire-tube in cylinder module of his construction as the heat exchanger, which it is.  I was led to believe that copper would not live in the furnace gases, because they can be up to 2000 degrees (C or F I'm not sure).  I assume that if you do go to firebrick, a water-tube exchanger would be easier?  In that case, do you recommend going for black-iron as Hobartian did? 

Hi Hobartian,

Thank you for those details.  I'm sorry that you had such a lot of trouble with your tank.  Sometimes the apparently simple things are what trips you up.  On the plus side, it seems that you have nailed the furnace side of things, which is the complex bit and the part that there is little info on the web about.  It would be very good if you could create a detailed HowTo showing what worked.  There are so many small details that still puzzle me, e.g the turbulators.

I just had another thought.  In your earlier post, you were concerned that the water in the heat exchanger was far hotter than in the tank.  Whilst your concerns were justified, it may still be desirable for the heat exchange water to heat up rapidly, in order to prevent soot build-up.  Most modern boilers have complex control systems that circulate water in a closed loop until the heat exchange water heats up.  I wonder if a simple thermostat in the thermo-syphon system may do the same job more simply?  Perhaps something like a car cooling system thermostat could work, opening at much lower temperature obviously.  This is only relevant if you do have soot problems.

My brother, who lives in Sydney, describes Australia as "the land of dry sticks", referring to the ease of obtaining dry firewood in the NSW Highlands.  I don't know if that would apply to Tasmania but if it does, maybe you won't have a soot problem.


----------



## tom in maine

I was referring to the water to water heat exchanger.
We have done a fair bit of work with copper heat exchangers in the boiler combustion area environment.
It can be used. There is not a lot of wiggle room when you lose circulation.
I have never melted one, but Dick has. It can happen quick.

Our current unit uses stainless steel (not tubing). It is always nice to be able to thermosyphon heat out of a boiler if flow is
interrupted. 
Murphy's Law rules Supreme in the universe!


----------



## Hobartian

The image shown was taken from the top of the wood feed chamber and shows wood burning in the primary combustion chamber.  The burning is extremely intense. 

It will be noted that creosote has formed on the walls of the feed chamber but this is normal as the chamber has a water jacket around it to inhibit the sticks of wood burning in the vertical direction.

The burning wood consists of pieces of the trunk of a hardwood tree that had a diameter of about 18 cm (7 inches)   I can easily fit three of these side by side.

I still have a number of modifications to make and the insulating to do.    In the mean time I am having fun!


----------



## Hobartian

A picture of the monster!  

 The elevated cylinder on the right has the purpose of storing the overflow of water from the main tank due to heat expansion.   When the main tank cools it should draw water back from the overflow cylinder.

I am using a tannin based treatment for the water to hopefully prevent corrosion.    There should be no air in the main tank.    A pressure relief valve set at ten psi is installed.


----------



## tom in maine

[quote author="Hobartian" date="1313412386"]The image shown was taken from the top of the wood feed chamber and shows wood burning in the primary combustion chamber.  The burning is extremely intense. 














Things of beauty. This is my latest' first burn. Something looks familiar!


----------



## Hobartian

Hi Tom,  

The pictures are indeed similar.    I presume your heater is based on Richard C. Hill's design.     The surface of the chamber looks very smooth.   What is the chamber made from?

I wish I had discussed making the heat storage reservoir with you before I started but I was not aware of your expertise in this area.   I was surprised at the forces generated along the flat sides even with very low pressures.   (5 psi)    In contrast when I built the water jacket around the wood feed chamber I was able to test it for leaks at sixty psi

At this stage I have not done anything about fitting turbulators.   That is something for the future.   What are you using?


----------



## tom in maine

We have spent about three years working on the current unit and are patenting it.
This is the fourth generation.
When I step back and look at it, it is obvious that Dick has had a lot of influence on me. His
reports have been available since 1976.
Before I knew Dick, I asked an associate of his, Norm Smith about how to build a chip burning boiler.
He suggested that this should be left to professionals and I might burn my house down.
You know what that advice led to...

Dick has been encouraging since day one and we have many stories of trying to burn things down!

The construction is all stainless steel. The photo was from the first firing. The fuel tube is darker now.
I will be firing it within a month. It had only been in service for about a month before the heating season was officially over.
Other than dealing with six months of cold weather, I am looking forward to it starting up again.

There is enough that is different inside that a patent is possible, although Dick and my patent attorney warn to the contrary.
There are a lot of prior art wood burning patents out there.

There are currently no turbulators in the unit. The stack temperature runs about 300-400 depending on the firing rate without them.


----------



## Snail

Is the hassle of pressurising the system to 10psi and possibly having to get the tank certified as a pressure vessel worth the extra 15 degrees Centigrade maximum storage temperature?  However, if it is pressurised, you may be able to use a car thermostat, if you need one to avoid soot problems.  (I believe modern cars use a 15 psi pressure cap, so you may need a thermostat from an older model though.)

I am a bit puzzled about the need for a water jacket for the fuel chamber.  Wouldn't the lack of air circulation alone be enough to encourage charcoal formation and the release of the volatiles?  If it was, wouldn't it be best to have the volatiles at as high a temperature as possible, in order to promote rapid combustion and thus minimisation of creosote deposits? 

When you open the hatch, to add more fuel, or to take photos, is there not a risk of escape of toxic, possibly explosive tar/creosote gases?


----------



## tom in maine

It is my humble opinion that the effort and cost involved in pressurizing the storage system is not worth the cost and effort.
Of course, I make my living manufacturing unpressurized tanks. 
The start of the whole thing for us was to find a way that was easier than moving and installing a pressure system involved when it came to large
storage tanks. 
We got to see a lot of site built tanks that did not work well. We also have spent about 30 years trying to develop a system that is simple and workable.
There is enough debate about which system is better. Both have strengths and weaknesses.
Fortunately, the temperature gap is less than it was, since we are now using a liner that is more tolerant of temperatures above the 160-170F that EPDM is limited by.


The water jacket on the fuel chamber is most important  for vertical fuel tubes.
The idea is to control the amount of pyrolysis. It is not perfect, but it tends to chill the fuel enough to keep it from burning up
the fuel tube. 
This only works to some degree, depending on the size of the fuel tube and other design issues.

Yes, the fuel tube can fill with smoke that can "bump" if oxygen is introduced too quickly.

Years ago, we have one unit that we were testing that had a vertical fuel tube that would shoot out a 6' flame that would lick the
ceiling! Fortunately the ceiling was two layers of 5/8" sheet rock. Big fun.

An induced draft fan helps minimize this problem and opening the fuel chamber door also helps.


----------



## thecontrolguy

> author="Snail" date="1313551602"]Is the hassle of pressurising the system to 10psi and possibly having to get the tank certified as a pressure vessel worth the extra 15 degrees Centigrade maximum storage temperature?  However, if it is pressurised, you may be able to use a car thermostat, if you need one to avoid soot problems.  (I believe modern cars use a 15 psi pressure cap, so you may need a thermostat from an older model though.)



I am in the boiler industry and it causes me some level of anxiety to hear of safety equipment (car thermostat) used incorrectly in place of proper safety equipment.  If your custom install NEEDS a safety relief, it should have a proper device that not only opens at the rated pressure, but can also blow off ALL the excess pressure generated by the heating equipment without allowing the pressure in the system to rise past the blow-off point.  You can easily turn off the auto engine when the t-stat opens and steam blows out the hood.  However, the wood fired equipment continues to make heat (and thus pressure).  We don't want to make steam bombs.  I AM SORRY if this sounds anti-experimental.  It is not intended that way. If it is okay to keep it non-pressurized, then do it that way.  IMHO, the 'European' method of using a tall riser to an elevated expansion tank, (say two floors up from the basement into the attic) is an elegant and safe way to apply some pressure to the heating equipment while still being an open system. (expansion tank is open to atmosphere)  This can also help to reduce the likelihood of cavitation in high-head pumps, and reduces oxygen infiltration into the open riser and then into the system causing increased corrosion in all parts of the system.  

This continues to be a very interesting thread and I hope it continues!!

Cheers!


----------



## Snail

A thermostat is not a pressure valve.  Pressure regulation is handled elsewhere.  The worst-case scenario is that the thermostat sticks shut and the water in the heat-exchanger boils.  The pressure release valve system would need to be able to handle the volume of steam, which is of course far more than the expansion of the heated water.  It should probably be designed for that even without a thermostat in the system.  
I don't have any expertise on pressure relief valves, I'd avoid pressurised systems like the plague, but the boiling itself need not be a major problem, based on my experience with unpressurised systems (You just get a minor geyser out of the roof vent-pipe).  
Car thermostats are highly reliable and when they do fail, it is almost always in the stuck-open state.  If this were not the case, we would hear of many  motors destroyed by the resulting overheating.  I have never even heard of this happening and I am very familiar with exceedingly old, high mileage vehicles.  In fact, in my experience, car thermostats are far more reliable than the electrical thermostats in Australasian electric hot water cylinders, which DO fail in the hot state occasionally.  
It is probably a good idea to make a very small bypass to ensure that whatever happens, the heat exchanger cannot boil dry until the entire tank has emptied.


----------



## Snail

Anyone seen this page?  http://www.afabusa.org/aldehyde_combustion.php
It hints at sophistication that is beyond anything I have been able to find details on in my googling.  Is there any way that a DIY constructor could access any details of these enhancements?  It's a pity that lambda sensors are such a horrible price.

The modularity of the Hill design would seem to make it possible to experiment with the combustion chamber?  

One idea that I have been playing with, in my head only, not in clay, is to have a sort of a cyclonic combustion chamber.  The primary combustion gases would enter at the cup-shaped bottom of the chamber via a nozzle that protrudes slightly into the chamber.  Secondary air would enter at the top of the chamber, via angled jets. The idea would be to have the secondary air spiral down the outside of the chamber and then be reversed by the cup and flow up the sides of the nozzle.  As the secondary air is forced into the centre, towards the nozzle, conservation of angular momentum will speed up the rate of spin.  The outside of the nozzle would be ridged to cause turbulence.  The result would be a highly turbulent, rapidly-spinning flame from the nozzle.  The flame would pass up the centre of the chamber and exit via a pipe that also protrudes into the chamber.  The secondary air spiraling down the outside of the chamber will be pre-heated by the flame before mixing  with the primary fuel-air at the nozzle.  The rapidly spinning central flame will throw out heavier material, such as tar aerosols, smoke and ash particles, which will be entrained in the secondary air and recirculated through the flame, until they are fully-burnt.

I know that this won't be as simple as I made it sound.  The devil is always in the details.  Anyway someone else is bound to have thought of it before me and the idea has probably already been tried and either patented, or discarded as unworkable.  Quite apart from the tricky aerodynamics (even basic cyclone separators are not trivial to design), the bottom of the cup may not heat up enough to prevent tar build-up.  Cleaning out the ash particles from there may also be difficult  to arrange.  I'd be interested in what people know and/or think about it though.


----------



## Wallyworld

Those pics look just like the Dumont I had. The hair on the back of my hands was gone every winter   , that baby burned with some intensity


----------



## jimbom

I look through Google patents for old technology.  Perhaps new technology may be displayed.  Many ideas are patented, but then for whatever reason never get introduced.


----------



## Hobartian

Hi Wallyworld and other members,

Quoting from Wikipedia:

Jetstream furnaces (later Tempest wood-burning boilers), were an advanced design of wood-fired water heaters conceived by Dr. Richard Hill of the University of Maine in Orono, Maine, USA. The design heated a house to prove the theory, then with government funding become a commercial product.

My heater and your old heater are siblings!

My heater has no commercial value due to its size and construction which would not allow it to be built and put on a pallet for delivery.   Nor does it have the sophistication of modern designs but then it's simplicity allows people like myself to build it for a reasonable sum of money.

I note that Europe seems to be driving the development of gasifier wood fired boilers probably because of their population and long periods of cold weather.

 Initially I considered building something based around a rocket stove but realized the small wood feed and burn chamber would not readily allow me to heat three hundred gallons of water.  Never-the-less,  the rocket stove has its place as it burns efficiently without the need for electric fans.

Another thing I would like to do is build the same type of heater only dispense with the heat exchanger and water and have the hot gases heat a large stone wall like masonry heaters do.   Controlling the temperature would be difficult but the whole thing would be much cheaper to build without water and plumbing.


----------



## Der Fuirmeister

JimboM said:
			
		

> This is interesting to me.  Thanks for sharing.  Tasmania must get a few shots of cold from the great south ocean.  Better hurry if this is to help this winter.



Jimbo,  He's in Australia........January is summer down under.......


----------



## pybyr

Hobartian said:
			
		

> Another thing I would like to do is build the same type of heater only dispense with the heat exchanger and water and have the hot gases heat a large stone wall like masonry heaters do.   Controlling the temperature would be difficult but the whole thing would be much cheaper to build without water and plumbing.



I am a great admirer of well-designed and well made masonry heaters- have seen them and felt them in action and they're a wonderful mix of some really well-refined concepts and some bulletproof simplicity...  

One factor, though, is, that there is nothing (unless you get into really exotic stuff like phase-change materials) that even comes close to water in terms of specific heat- how much heat energy is stored in a given available amount of space/ weight.  And a water-based system lets you keep that heat banked and then circulate it if/ as/ at the pace needed....  Systems that run on pure passive thermal mass of masonry or stone end up being like big flywheels, and if you "rev it up" too hard compared to the way the weather happens to play out, you're suddenly (and sometimes for quite a while) baking in it...


----------



## Snail

Hi Hobartian,

Guess that Spring is sufficiently advanced by now and you won't need your furnace for a while.  Any update on how it has been going?


----------



## Hobartian

With winter not far away in the southern hemisphere I finally have the storage tank fully insulated and the heater is ready to fire!

This will be the first season that the heater will be used on a full time basis.


----------



## TCaldwell

very impressive, how many lbs wood and btu output do you expect


----------



## ozzie88

Hobartian said:


> Thanks Snail for your post.
> 
> I will be encasing the burn chamber and the secondary chamber with vermiculite cement but that will be done last as once it is done it will be difficult to undo.
> 
> You raised the issue of the way I have connected the heat exchanger to the storage tank.
> 
> Originally I intended to do this with two rigid rectangular pipes that each measured about 120mm by 60 mm. I thought the sheer size of the two pipes combined would be enough for the heat to equalize by convection. However, this did not work as the movement between the heat exchanger and storage tanks due to expansion and contraction fractured the connecting joints. Presently I have the tanks joined by a 50mm stainless steel flexible hose. I test fired the boiler today using only a small amount of firewood and I observed there was a huge temperature difference between the heat exchanger and the storage tank. I recorded 88 C in the heat exchanger whilst the water in the tank was only 28 C
> 
> I think I will modify the system by installing a 50mm pipe from the top of the heat exchanger to the top of the storage tank. I will then install a pipe from the bottom of the storage tank to the bottom of the heat exchanger. That should enable a good thermosiphon loop.
> 
> In regard to adjusting the air input that will be a matter for future experimentation. From my memory of reading Professor Hill's papers, the design allows the fire to draw the amount of air that it needs.


 Finally someone else who built there own boiler. I built my own and you really understand how all this works and how touchy things can be.
 I looked at your photos and drawing looks like it should work.  You may find that the air adjustments will be VERY fussey to get correct, just the little difference will make big change in fire.  Keep the idea that you may have to work on this or change parts when building.  Also I see there only one place to get air into fire? What I found out is when I added an air inlet at the end of second chamber I got the flame to burn longer and more complete, just a little to much will kill the flame.  I got between 78% and 84% when I checked it Lbs. of wood and burn time etc.  My boiler is an up-draft so I blow air in bottom, then in the top of bottom chamber then the second chamber then just a very little in end second chamber.  When I got it all fireing right i can start with say 120* water fire up takes 6 to 12 minutes to get secondarys to fire then adj. air once and off it goes.  I have peep holes so I can see the fire in chambers this is something you should think of, WOW can you see what a very little adj. of air can do to the flame, and fun to see your creation inn action. anyways..  Hope this may help,, good luck keep us posted.


----------



## ozzie88

Hobartian said:


> Thanks Snail for your post.
> 
> I will be encasing the burn chamber and the secondary chamber with vermiculite cement but that will be done last as once it is done it will be difficult to undo.
> 
> You raised the issue of the way I have connected the heat exchanger to the storage tank.
> 
> Originally I intended to do this with two rigid rectangular pipes that each measured about 120mm by 60 mm. I thought the sheer size of the two pipes combined would be enough for the heat to equalize by convection. However, this did not work as the movement between the heat exchanger and storage tanks due to expansion and contraction fractured the connecting joints. Presently I have the tanks joined by a 50mm stainless steel flexible hose. I test fired the boiler today using only a small amount of firewood and I observed there was a huge temperature difference between the heat exchanger and the storage tank. I recorded 88 C in the heat exchanger whilst the water in the tank was only 28 C
> 
> I think I will modify the system by installing a 50mm pipe from the top of the heat exchanger to the top of the storage tank. I will then install a pipe from the bottom of the storage tank to the bottom of the heat exchanger. That should enable a good thermosiphon loop.
> 
> In regard to adjusting the air input that will be a matter for future experimentation. From my memory of reading Professor Hill's papers, the design allows the fire to draw the amount of air that it needs.


 Finally someone else who built there own boiler. I built my own and you really understand how all this works and how touchy things can be.
 I looked at your photos and drawing looks like it should work.  You may find that the air adjustments will be VERY fussey to get correct, just the little difference will make big change in fire.  Keep the idea that you may have to work on this or change parts when building.  Also I see there only one place to get air into fire? What I found out is when I added an air inlet at the end of second chamber I got the flame to burn longer and more complete, just a little to much will kill the flame.  I got between 78% and 84% when I checked it Lbs. of wood and burn time etc.  My boiler is an up-draft so I blow air in bottom, then in the top of bottom chamber then the second chamber then just a very little in end second chamber.  When I got it all fireing right i can start with say 120* water fire up takes 6 to 12 minutes to get secondarys to fire then adj. air once and off it goes.  I have peep holes so I can see the fire in chambers this is something you should think of, WOW can you see what a very little adj. of air can do to the flame, and fun to see your creation inn action. anyways..  Hope this may help,, good luck keep us posted.


----------



## slowzuki

Just to add to the thread, the cyclone style chamber was present in the bioburner that was spun off by Woodmizer.  The cyclone action helps scour the flyash etc off the cold heat exchanger walls too.  Looking at their current design, I think they have moved the cyclone to after the heat exchanger?  Can't quite tell.

BTW, careful of the wikipedia entries on the Jetstream etc, why?  Because I wrote most of it!  I gathered more information over time from speaking to other people, theres a big error about the Tempest in some versions that got copied around.  I did get to speak to the surviving members of Hampton and also to the designers at Kerr that took over.  I have the last prototype that Hampton produced with an increase burn chamber diameter for softwood sitting in my shop.  I have no idea what to do with the thing, it was outside in PEI for who knows how many years.


----------



## maple1

Too bad Kerr didn't stick with the Jetstream - I'd likely have one now if I could buy a new one today. Just drove by the plant today, actually.


----------



## Hobartian

I have not been using the heater on a regular basis as the weather has only been cold on occasions. However, I have fired it on a number of times and it has worked perfectly.

Recently, I started the heater and added timber and when I came back some hour later I was quite alarmed to find the water in the tank at 98 C or 208 F. This is too close to boiling for my liking and I have since installed a thermostat to stop the fans at 95 C. Whilst I have two pressure relief valves installed in the tank I don't want to lose any coolant or potentially damage the tank.

I have been experimenting on the technique to start the heater.  I place a few inches of small pieces of timber on the floor of the combustion chamber and then a hand full of of a dry kindling on top with a wax fire-starter.  I then light the starter with only the exhaust fan running.  After a few minutes I start the main inlet fan and come back about ten minutes later and load the wood chamber with heavy long pieces of timber. It is quick and easy to start.


----------



## hobbyheater

Hobartian said:


> Recently, I started the heater and added timber and when I came back some hour later I was quite alarmed to find the water in the tank at 98 C or 208 F. This is too close to boiling for my liking and I have since installed a thermostat to stop the fans at 95 C.


 
The refractory can store a lot of heat. You may want to shut your fan off a few degrees earlier.
I run a Jetstream with 1,000 gallons storage and for example, after a 7 to 8 hour burn with the  storage at 195 top and the bottom at 170, I will run the circulator for another 3 to 4 hours after the fire is out and will see a 5 to 10 degree increase at the bottom.

It looks like your boiler has a large refractory component so I have attached a picture of a Jetstream refractory liner that is around 700 lbs and a complete base at 1,000 lbs just for comparison.


----------



## Eric Johnson

Very nice looking project. Hope it works as good as it looks.

I believe Prof. Hill's basic design is the one most modern gasifiers are based on, but I could be wrong about that. I'm sure slowzuki could give us a bit more history on that--despite being a Wikipedian. He's Canadian, too, but I'm not holding that against him--too much.


----------



## ISeeDeadBTUs

Two returns from the dead in one thread . . . 

And Hobart?? You get absolutly ZERO style points for that beast!!


----------



## Hobartian

Thanks for the comments. 

I admit my heater does not have much style and would be difficult to sell commercially.   However, it does work and can be be built at home by someone who can weld and generally construct things. 

In Australia there is very little use of hydronic heating.   Reverse cycle  air conditioning is most frequently installed because of the relative low cost to buy and install the units. (Thanks China)
 However, many are finding them very expensive to run due to the sharply rising cost of electricity.   

Hobbyheater:    The Jetstream refractory liners look very impressive.    Their cost must be quite high but they look as though they would last.


----------



## hobbyheater

Hobartian said:


> Their cost must be quite high but they look as though they would last.


 

The cost was very high but has proved to be worth the investment as they are very repairable. https://www.hearth.com/talk/threads/giving-a-jetstream-base-new-life.76371/
 A familiar picture
I had been following your project for sometime before becoming a Hearth member. Very impressive


----------



## Mark Holden

Hobartian;
Thanks for sharing your work; I'd come across Hill's paper before, but your up to date step by step progress brings it alive.
I have the skills and [hopefully] the experience to do something similar for my place in southern Portugal.
I'd also feel more confident using insulating firebrick, having used it before to build a ceramic kiln. but I'm considering your [and hill's] method.
Your  experiences in construction and firing your burner are really useful.
Do you have any idea what your combustion temperature is? What about the temperature in your flue [that would say a lot about your heat exchanger]?
It looks like all the combustion air is introduced at 1 point, with no secondary air ports; that sure makes it easier.
On the other hand, there is no pre-heat for the combustion air. I guess it doesn't matter all that much, as long as you achieve combustion temperature that's high enough.

I would eventually add solar collectors to my system, and hope to get 90% of my heat from them. I've done a lot of research on this.
I've made lots of tanks [big and small] for fuel and water in the past, but for this I'm thinking a big scrap LPG tank of around 1000 gallons. I found some not too far from here.


----------



## Hobartian

Hi Mark

It is my understanding that Professor Hill now advocates building the fire chamber from firebrick.  It appears either method of construction works.   It is yet to be determined whether my burn chamber will stand the test of time.   I didn't spend much money on the chamber as I wanted to find out whether the heater would fulfill my needs.


I haven't measured the temperature in the combustion chamber but I know there is no build up of creosote in the heat exchanger.   The stack temperature when the heater is in full operation is in the region of 400 C.    The inlet air is preheated as it is delivered through a stainless steel pipe which I bent in a circular shape and is embedded in the wall of the burn chamber which reaches a very high temperature in operation.

A tank of one thousand gallons sounds fine to me.  My storage is about 350 gallons and I wouldn't advocate anything smaller.

Good luck with the solar collectors.   Maybe you can design your system to use both forms of heating.    The wood fired boiler will heat the water  in your storage tank overnight rain hail or shine as long as you feed it with timber!


----------



## woodsmaster

do you mean 400 F     400 C = 752 F. That would be sending a good amount of heat up the chiminey.


----------



## Hobartian

woodsmaster said:


> do you mean 400 F 400 C = 752 F. That would be sending a good amount of heat up the chimney.


 
I have not yet installed turbulators in the heat exchanger which should reduce stack temperatures and improve overall efficiency.    On the other hand,  having the tubes open makes it very easy to check them to see if they need cleaning.   I know I have plenty of heat on hand and losing some up the chimney hasn't been a worry to me.


----------



## Mark Holden

400C stack temperature... it seems so wasteful! but I don't know what is "normal". I guess you can always add another heat exchanger to the stack if you want.
I'm also curious about the burn chamber; can it handle unsplit logs, or do you need several split pieces to burn?
I ask because I'd mostly cut my own wood from my pine forest. splitting wood isn't my idea of fun.
On the other hand, building a wood splitter IS my idea of fun...

my design is intended to be mainly solar, but I won't be able to build the collectors for a while. I want a very gig array, capable of heating the house while adding heat to the buffer tank during sunny winter days.
In the meantime, the woodburner would have to do all the work.


----------



## Mark Holden

An oil fired boiler in a rental property I have has the kind of thing you want;
The design is pretty similar to your heat exchanger, with 1-1/2" [as I recall] flue pipes from a burn chamber rising through a water tank. Vertical instead of horizontal.
There are lengths of twisted strip hanging in the tubes from the top. to clean them and the tubes, it's necessary to pop the top off the boiler to pull them out. I don't know if they're made from a clever material, but I assume they are. After several years of heavy use, there was no visible erosion.
You would find something like that from a company that sells heating system parts.
It would be interesting to know how it affects your system if you add them.


----------



## Hobartian

I have some reservations about the design of my wood fired boiler. 

Professor Richard C. Hill mounted his heat exchanger in a position so the steel tubes were running vertically.

I chose the opposite thinking it would be easier for me to clean the tubes if they were horizontal and close to the ground.   However,  I did not realize the amount of fly ash that is created in the burning process and in my case this fly ash is being carried through the tubes accumulating on the floor of the tubes and at the end of the heat exchanger.     When this ash accumulates the efficiency of the heater is significantly down graded but is restored when I physically remove the excess ash.

My problem is that the force of gravity is not helping me whereas in Professor Hill's design the ash has a much better chance of falling down into the clean-out chamber. 

I will continue to use the heater and possibly in the off season I can work out how I can modify the design to prevent so much fly ash from being introduced into the heat exchanger.


----------



## Mark Holden

I guess now we know why the tubes were designed vertical...
I clean out the tubes in the aforementioned oil burner once every year or two, and it is a pain.
Like your situation, it's in a tight spot, and I have to wrestle the flue pipe out of the way, then work in the small space above.
So I can see why you built your as you did.
Once again, thanks for sharing your findings; it may well save someone from repeating your mistake.
"Someone" could even be me!


----------



## Eric Johnson

I'm not sure how you'd build one, but an ash-removing cyclone might help. Might be easier than re-orienting the tubes. At least one gasification boiler on the market employs one.


----------



## Hobartian

Over the past fortnight the performance of my heater deteriorated.  The stack temperatures dropped to a figure hovering at around 180 to 220 C.  The heating of the storage water was painfully slow and I could smell a slight pungent odour.   Looking down into the fire it didn't seem to have it's usual intensity.     I couldn't work out what was wrong and I started to think the problem lay in the timber that I was burning.  I tried different types of timber, chopping them into smaller pieces all to no avail.   Then I had the thought maybe the air inlet pump was faulty.  While investigating I removed  the inlet air filter.  (A cheap part made in China and bought for a few dollars)   The heater surged into life and the intensity of the burning was tenfold.   The stack temperature quickly climbed and the temperature of the storage water increased noticeably.   Apparently the filter was restricting the flow of air which severely impeded the performance of the heater.     Currently,  I am running the heater without an air filter until I can fit another with a much larger capacity.    Of course the air does not need to be filtered for feeding into the fire but I am concerned that damage could be caused to the internal parts of the Gast Regenair air pump in using it without a filter.   Fun and games!


----------



## Mark Holden

Wouldn't a simple screen do the trick? expanded over a protruding frame perhaps?
I'd think anything small enough to pass through [dust] wouldn't harm anything.
What are the specs on the air pump by the way?


----------



## woodsmaster

Mark Holden said:


> Wouldn't a simple screen do the trick? expanded over a protruding frame perhaps?
> I'd think anything small enough to pass through [dust] wouldn't harm anything.
> What are the specs on the air pump by the way?


 
I may be totaly wrong but I'm thinking a screen would probably plug up and or posibly melt. If you could clean it easy and the temps at the screen were low enough it may work.


----------



## hobbyheater

Hobartian said:


> I I did not realize the amount of fly ash that is created in the burning process and in my case this fly ash is being carried through the tubes accumulating on the floor of the tubes
> I can work out how I can modify the design to prevent so much fly ash from being introduced into the heat exchanger.


 
The Jetstream needs to have the bottom of the burn chamber cleaned before every firing. This is accomplished by using the the long handled scoop pictured below.  I prefer to use an ash vacuum.  If the burn chamber is not cleaned before each firing, it does not take long before the settling chamber gets plugged and so on up the chimney.


----------



## Hobartian

I continue to learn as I use my wood fired boiler as there are so many things to observe. I have previously posted information on this forum that I would like to comment on further.

*Stack temperatures.* I previously stated it was in the region of 400 C. (750 F) It does exceed this figure on occasions but of late it has been running at about 240 C (464 F) The stack temperature can vary quite markedly. However, I am happy to see it on the high side rather than on the cool side.

*Fly ash in the heat exchanger* I previously stated I was having a problem with fly ash carrying through the heat exchanger. This problem only occurred when the inlet air filter became blocked and the fire was not burning with it's full intensity. After replacing the filter the problem with the fly ash is no longer present. I can only presume that with a hot fire the ash is almost fully consumed. I have taken note of Hobbyheater's suggestion to remove the ash from the burn chamber on a regular basis which doesn't take long using a tin on the end of a stick followed by vacuum cleaning.

I finally got around to encasing the burn chamber with a mixture of vermiculite and portland cement. This has made a significant difference to the efficiency of the boiler as heat is retained in the burn chamber for a much longer period of time which makes starting a new burn much easier.

*Comments about wood to be burnt*. I do not buy timber to burn and scrounge around to find anything I can burn. In this regard timber that others leave behind such as tree stumps and gnarled remnants burn fine in my boiler. Whilst sticks burn with the greatest intensity I have found I can burn very large single pieces of wood if they are loaded when the fire is at fully established and running hot.

*Temperature of water*. For efficient heating with panel radiators I have found the water needs to be at least 70C (160 F) or hotter. Yesterday I heated the water to 98 C and the heating was magnificent. However, I consider that degree of heat too high for safety.





The new air filter



Rough pieces of timber that I can burn



The burn chamber encased with insulating cement



Too hot for safety!


----------



## Mark Holden

Thanks again for sharing your results!
I'm curious about your air supply; it looks a bit fearsome, more of a high volume compressor than a fan.
What is the intake air volume, and what [if you know] is the operating [burn chamber] pressure of your boiler? This would be really useful info from an engineering point of view, for design calculations of the burn chamber as well as the machinery.
I have a leftover 1/2hp squirrel cage blower I was thinking of using. It's a high pressure blower, but nothing like yours.
I was also considering using an oil burner I have [25kw]; it could start the wood fire, then I could cut the oil flow and only use it's blower. It might even work as a backup heat source. But after seeing your blower / compressor, I don't thing the little one in the oil burner could do a thing for me.


----------



## Hobartian

Hi Mark,

In Professor Hill's paper he recommended using an R1 series Gast Regenair blower which is rated at 1/8 hp. When I was looking on Ebay in USA for a used unit I could only find an R2 series which is rated at 1/5 hp .
The price was right so I decided the extra capacity would not hurt and that has proved correct.

Currently there are some R1 series blowers for sale on Ebay.
http://www.ebay.com/sch/i.html?_kw=GAST REGENAIR BLOWER R1102

This is the specifications for the R2 pump which should provide the information you are seeking.


----------



## Hobartian

This is a picture looking into the burn chamber taken after a burn was completed. All that is left of several large logs and odd pieces of gum trees is a few handfuls of fine grey ash. If the planet heats up as a result of global warming I guess I could always go into the cremation business.


----------



## Mark Holden

I actually built a one-use crematoria last week; wife wanted to keep the ashes of our dog.
Just an oil barrel with fiberglass on the outside , a grating halfway up, and a half lid.
Burned at 550-600C powered by an oil burner through a hole near the bottom, temporarily pulled from our heating system for the job.
I had the burner turned down to minimum, about 12kw, to avoid meltdown; but higher temp would have been better for breaking down the bones.


----------



## Mark Holden

You r blower shows max pressure is 30" of water [50hz], which is about 0.07bar; and 33cfm, which is about 1 cubic meter per minute.
Is that right? It seems like a really small amount of air.


----------



## hobbyheater

Mark Holden said:


> You r blower shows max pressure is 30" of water [50hz], which is about 0.07bar; and 33cfm, which is about 1 cubic meter per minute.
> Is that right? It seems like a really small amount of air.


 
The Jetstream uses a  two stage vacuum cleaner motor rated at 99 cfm at 84.5 inches of water lift.  http://www.centralvacuummotor.com/Product Bulletin/116311-00.pdf


----------



## Hobartian

In my instance I didn't experiment with different fans as I wanted to closely follow the original design of Professor Richard Hill. If you read his paper he certainly tried many options and settled on the Gast Regenair R1 Series for input air and the Djernlund Draft Inducer Model DJ-3 for the exhaust. Quite frankly I had my hands full in building the heater and following the Professor's advice gave me the best chance of a positive outcome. The two stage motor in the Jetstream certainly seems to have high performance but I don't know whether it is still available and I don't know the details of the manifold that it feeds into.


----------



## Mark Holden

It's true, all the numbers are clearly laid out in the original paper. Dr. Hill wrote his burner ran at 3" [not 30] water pressure [excuse me, but I find this a slightly archaic form of pressure measurement], and only around 24cfm of air volume. He says that includes lots of excess air to ensure complete combustion too.
I don't much like the induced draft flue fan; if heat extraction is very good, there would be little convection to pull out the exhaust, and the fan will survive. But if my home made heat exchanger isn't so great, the hot exhaust would likely kill the fan. And it wouldn't need it either.
I would like to use stuff I have left over and lying around; but all my stuff is either too big or too small...


----------



## hobbyheater

Hobartian said:


> I don't know the details of the manifold that it feeds into.


 

On the Jetstream, one vacuum motor does double duty as both draft inducer and forced draft. As shown in the last picture, the motor was originally mounted on the back of the boiler. In this configuration, the motors were short lived; they just ingested too much dust from the boiler. The first picture shows the vacuum motor mounted on the boiler room wall where it gets clean outside air from a duct in the basement wall. Second picture shows the air being divided between the draft inducer and the forced draft. Third picture is the draft inducer port in the chimney. The fourth shows the air is preheated as it passes through settling chamber above the tunnel and into the burn chamber.
Building your own boiler that works is impressive! Hope this info can be of some use.
The vacuum motor is still available.


----------



## BoilerMan

Thats the kind of draft inducer I like! One that is pnumatic, and not a motor with impeller in the exhaust, putting the motor close to the heat, or with a really long shaft. Use the venturi effect to "pull" the smoke out.

I just read Dr. Hill's full report (his name is still famous in Maine) very interesting stuff.  HH: what do you think of the Madawaska version? There is a thread of one for sale. Must weigh several tons like your Jetstream.

TS


----------



## hobbyheater

Taylor Sutherland said:


> HH: what do you think of the Madawaska version?
> TS


Looks heavy, but like the Jetstream, would be very repairable .


----------



## Mark Holden

HH, thanks for uploading the pictures. A Venturi draft inducer seems a better idea to me; Professor hill said he found them to be too inefficient.
But I have a leftover 1/2hp scroll fan that has a fairly high pressure output; a bit of creative ducting and it should do everything.

Those industrial vacuum motors are nice, but I have to work with a very small budget. Cash is thin on the ground out here, and stuff like that costs double in Europe what it does in the US.

We pay $5.70 a US gallon for heating fuel, $6.84 for road diesel, and $7.93 for gasoline. skilled labor is worth $10 per hour, or would be if there was any work.
And just for good measure, we're in severe drought!
The weather is nice though.


----------



## woodsmaster

Mark Holden said:


> HH, thanks for uploading the pictures. A Venturi draft inducer seems a better idea to me; Professor hill said he found them to be too inefficient.
> But I have a leftover 1/2hp scroll fan that has a fairly high pressure output; a bit of creative ducting and it should do everything.
> 
> Those industrial vacuum motors are nice, but I have to work with a very small budget. Cash is thin on the ground out here, and stuff like that costs double in Europe what it does in the US.
> 
> We pay $5.70 a US gallon for heating fuel, $6.84 for road diesel, and $7.93 for gasoline. skilled labor is worth $10 per hour, or would be if there was any work.
> And just for good measure, we're in severe drought!
> The weather is nice though.


 

  And I thought it was getting bad here.


----------



## Mark Holden

I'd move back to the US [been away for 30 years] if I could sell; but the banks won't / can't finance, and there are no buyers for now.
So to keep myself amused I'll try to build the boiler, if I can do it on a shoestring.
Every buck I invest here raises my property value by 25 cents, if I work for free.


----------



## Frozen Canuck

Mark Holden said:


> I'd move back to the US [been away for 30 years] if I could sell; but the banks won't / can't finance, and there are no buyers for now.
> So to keep myself amused I'll try to build the boiler, if I can do it on a shoestring.
> Every buck I invest here raises my property value by 25 cents, if I work for free.


 

OUCH!


----------



## junkers

Mark Holden said:


> We pay $5.70 a US gallon for heating fuel, $6.84 for road diesel, and $7.93 for gasoline. skilled labor is worth $10 per hour, or would be if there was any work.
> And just for good measure, we're in severe drought!
> The weather is nice though.


 
 it is not so bad in Portugal, fuel prices are the same
  I only work for half the price of an hour


----------



## Hobartian

*Hi Jebatty,*

*I have read your posts about installing chain turbulators in a Tarm.*

I am considering installing turbulators in my home built boiler. My boiler has twelve fire tubes running horizontally which are about one meter long with an internal diameter of approximately 38mm (1.5 inches)

One option is to use chain about four mm smaller than the internal diameter of the fire tubes. I have thought about whether an accumulation of fire ash may make it difficult to withdraw the chains to enable cleaning. My experience up to now is that the ash in the tubes has been fine and soft and thus easy to remove.

I note that you used chain of a much smaller diameter that the fire tubes in the Tarm but you were able to centralize the chains by the method you used to suspend them. If I use a smaller diameter chain it will lay in the bottom of the tubes with a large gap at the top which would probably defeat their intended purpose.

I would be interested in your opinion in this matter given your experience with turbulators.

*JEBATTY's RESPONSE *

Horizontal tubes present an issue. With vertical fire tubes some boilers (Froling, for example) use a helical coil turbulator mounted to a frame which allows the turbulator to slide slide back and forth by a manual lever to shake the ash from it and to clean the fire tube. The coil is in contact with the sides of the fire tube.​​A similar chain device might be used, perhaps with a rod to hold the chain rigid, or perhaps welding the links of the chain to make the chain rigid, along with a shaker assembly. The weight of the chain might cause the chain to sag, especially under heat, and make this impractical though.​​My general thought is that any device which turbulates the hot gases in the fire tubes, and not be too restrictive on gas flow, will achieve a beneficial result. When I talked to Tarm about the chain idea, I was told that their commercial turbulators resulted in about a 100F drop in stack temperature. The chain turbulators also achieved this outcome, so I guess they worked about as well as the commercial ones.​ 
T*hanks Jebatty for your quick and considered response.*

​I had thought of buying twelve meters of chain but it might be prudent for me to buy only one meter and experiment with it to find out a practical way to install it. Welding the links is certainly an option for me.​


----------



## Hobartian

I now have turbulators installed in my heater. Each turbulator is one meter long and made from heavy mild steel chain. All the links are welded together so the chain is straight and rigid. The chain is easily pushed into the boiler tubes as the width of the chain is about one quarter of an inch narrower than the boiler tube.

Preliminary testing has shown a dramatic reduction in stack temperatures which are about half of what they were.  Long term testing will be needed to gauge the worth of having the turbulators installed but as summer is fast approaching in this part of the world that may have to wait until next season.


----------



## Hobartian

Hi Hobbyheater and other members.

Now that summer is approaching I am planning on rebuilding the fire chamber of my heater which is crumbling and may soon collapse completely.

When I built the chamber I used  high temperature refractory but did not follow the manufacturer's instructions on curing by progressively baking the casting at a range of temperatures.

I have read where people use stainless steel needles for reinforcing refractory.    Have you any knowledge about this, or other tips which may help me to complete the task?

Thanks


----------



## dmachado

Hobartian said:


> Hi Hobbyheater and other members.
> 
> Now that summer is approaching I am planning on rebuilding the fire chamber of my heater which is crumbling and may soon collapse completely.
> 
> When I built the chamber I used high temperature refractory but did not follow the manufacturer's instructions on curing by progressively baking the casting at a range of temperatures.
> 
> I have read where people use stainless steel needles for reinforcing refractory. Have you any knowledge about this, or other tips which may help me to complete the task?
> 
> Thanks


 
Hello Hobartian,

I too am building a wood boiler, but I am using refractory brick and a different approach, i'll post it as soon as I get it up and running, here's a pic from the early stages:






My advice is to use firebrick for the burn chamber, insulated, you can repair/replace it easily, and it keeps the burn temperature very high. Good luck.


----------



## Hobartian

Hi Demachado,

I have considered using firebrick but I would like to have another go at casting the chamber using a much better technique that will allow the proper baking of the components before they are put into service. In the first instance I did not follow the manufacturer's instructions and thus have only myself to blame.

I would certainly like to see more pictures of your heater and hear about it's performance. Where did you get the design? Is it fan assisted? Is it a gasifier?


----------



## dmachado

Hello,

I hope it performs well, as soon as I get it running! I got the ideas from rocket mass heaters and also from masonry heaters, then I fitted a water jacket in there...

It will be fan assisted (low cfm) to keep the burn rate efficiency high, it's a firebox with a stainless steel exchanger under the refractory floor, and a water jacket with "turbulators" on the flue side... I'll use the top down burn to get the most out of the wood and no smoke burns so the neighbours are never disturbed by the smoke. 

As soon as I create my own post I'll you know about it. 

You have an excellent work there, by the way.

Regards.


----------



## peakbagger

I installed a large thermal oixidizer many years ago used as a backup disposal device fora  hazardous gas stream. It would sit off line at room temp and then have to go up to 1600 deg F in 20 minutes. The refractory in the burner really didnt like it. We found that if we followed the initial cure instructions when we replaced the refractory, we would get longer life, but it was real easy to skip steps and if they were skipped the refractory didnt last as long. I have seen the use of stainless steel needles, it tends to keep the casting together when it starts to fail but I didnt see any signficiant  life extension. It was PITA to take out refractory that has it in it.  The majority of the unit was lined with ceramic blanket, that worked very well, we had several years on it and it was in fine shape.


----------



## Mark Holden

There are different grades of firebrick; hard brick doesn't insulate, and insulating brick is quite soft and can easily get crumbly.
If building this type of high temperature burner using brick, the best is to line the burn chamber with hard fire brick, then put a layer of insulating brick around that, then an external cladding.

I built a ceramic kiln that ran on kerosene, it fired at 1050C and sounded like a 747 taking off.

Thanks for the update on the turbulators; that's useful information!


----------



## Hobartian

During the summer months down under I have been busy rebuilding the primary and secondary chambers of my wood boiler and have some pictures to display.

The burn chamber was caste in five parts using high temperature refractory and the pieces were butted together and held firmly in place inside a steel drum and surrounded by refractory insulation.

A tube leads to the new secondary chamber which has a steel outer casing and is lined with firebricks and refractory insulation. A clean-out port is installed in the top of the secondary chamber.

The outlet from the secondary chamber feeds heated air to the heat exchanger.

The blue drum on top of the wood feed chamber is to contain flames that may leap out when dropping wood into the chamber. (This does not happen if the air supply fan is switched off)

The flow of cold water into the heat exchanger is controlled by the motorized 2 inch ball valve and a thermostat.

Air is fed into the burn chambers by fourteen stainless steel tubes in a manner to cause swirling  and great turbulence.

I am now waiting for some cold weather to give the heater a test run with the new components installed.


----------



## Mark Holden

Wow, you've really done a lot of work there; it looks great.
I'd like to know more about the refractory lining; did you make those sections yourself? The fit looks really impressive. I would think the segmented combustion chamber will be able to expand and contract a bit as necessary without cracking.


----------



## Hobartian

Hi Mark,

I made the sections myself.   I had as friend in an engineering business roll pieces of steel for the inner and outer faces of each mold.   The sides and bottom of the molds were cut from plywood.  As I filled the molds with refractory cement I vibrated them by placing them on top of the running four stroke motor of my high pressure cleaner.  (All high tech!)   The cast pieces were kept damp for a couple of days and then allowed to dry naturally for a week.   I then baked them in my kitchen oven for about eight hours.  (I tried to get them fired professionally but I couldn't find anyone who was game to take on the task)

I made the burn chamber in pieces for ease of handling and because a monolithic structure would most likely crack as you have pointed out.   I put a lot more effort into making the burn and secondary chambers than I did initially and  I am hoping for a longer service life.


----------



## mikefrommaine

Did you use refractory needles?

I've used an old vibrating palm sander on top of concrete molds with success in the past.


----------



## arbutus

Excellent work.

I doubt you will have problems with the refractory cast in sections as you have done, but I feel compelled to offer a word of caution.
This winter all three of the boilers at my workplace decommissioned themselves after having the firebox burn through at a joint in similarly cast refractory.  The flame had burned through 3/8" plate steel after seeping through a joint in the refractory!  The boilers are 16 years old.

I feel a tongue and groove section or mating lip cast into the edge of each piece may have prevented this erosion.
You are certainly dealing with far less power - these boilers are rated at 150 hp - and it may not be a problem at all, but I do encourage you to keep the joints as close as possible and watch for any signs of erosion.


----------



## Hobartian

Thanks for the responses.    

I didn't use refractory needles as I read a number of opinions online that needles would not extend the life of the refractory.

 I applied furnace cement to the joins during assembly and packed high temperature refractory insulation behind each joint with a two inch overlap.  (I will keep my fingers crossed)


----------



## Snail

Hi Hobartian,

Great job as usual.  Was your original construction becoming really decrepit or is this new work mainly your perfectionism in action?

I have still not started on mine.  Got too busy with paid work overseas.  However I have just posted a thread with my ideas, if you are interested.
https://www.hearth.com/talk/threads/concept-for-diy-furnace.109736/

You can see I am really trying hard to make the heat exchanger easier to build. Related to that, how ofter have you found cleaning the fire tubes in your boiler is really necessary?

Peter


----------



## Hobartian

Hi Snail,

The new work was unavoidable as the original clay pots lined with refractory materials crumbled into a multitude of pieces. The new design has everything contained within steel casings which should help to hold things together.

The addition of the control valve to feed the storage water into the heat exchanger is designed to avoid water contained in the flu gases condensing in the heat exchanger when the water in the storage tank is relatively cool.

In regard to cleaning the fire tubes: In the original design my secondary chamber was too small and did not allow flu ash to fall before the gases entered the heat exchanger. This caused an ash build up in the fire tubes which needed to be cleared after a few weeks. However, there was never any creosote buildup which is the most important thing to avoid.


----------



## Hobartian

I have fired the boiler a couple of times and all is going well.     I took the displayed pictures with the risk of burning my hands.

The first picture shows the primary burn chamber as viewed from the top looking down through the wood feed chamber.

The second pictures  shows the interior of the secondary burn chamber and was taken looking through the clean out port.    You will note there is ash and debris on the floor of this chamber where it has fallen in lieu of passing through the fire tubes of the heat exchanger.


----------



## BoilerMan

That looks great, nice and clean in the secondary!  I still have to admit, it is looking more and more space age.  What it the 55 gal drum with the cutout over the loading door used for other than to house the light?  Have you considered some type of thermostatic valve in leu of the ball valve for cool water HX protection?

TS


----------



## Hobartian

Hi BoilerMan,

Yes, my contraption is getting more sophisticated.

The 55 gallon drum with the cutout is there to contain any flames that may leap out when loading wood into the burn chamber. This is substantially reduced if the supply air fan is turned off before the loading door is opened.

The ball valve metering the flow of cool water into the heat exchanger is motorized and I am using a STC-1000 thermostat to control it. (The end result would be similar to a thermostatic valve.)


----------



## Mark Holden

I was a bit worried about your sections cracking, as you hadn't been able to get them fired in a kiln [I have some ceramic experience]. I'm glad it's passed the first test.
I'm curious about the material you used; refractory cement you wrote. is that a product you were able to buy  essentially ready to use? Is it intended as an insulator or only as containment?
I'm in rural Portugal and material is hard to find, especially if I don't know what I'm asking for.
If my property isn't sold, I intend to start work on my system this summer.
Not much is selling here...


----------



## Hobartian

Hi Mark

Only time will tell how long the castings will last but really I feel quite optimistic. The castings were kept damp for a few days and then allowed to dry for a couple of weeks outside in the sun with low humidity. Then I baked the pieces in a domestic oven for about eight hours at 200C




This is the manufacturer's description of the product I used.

(RE Real Estate in Hobart. Very little is selling here too!)


----------



## BONE

Hobartian, congratulation on your project,would like some info if poss ,is your heat exchanger a standard propane tank with 2" tubes welded ,im thinking of adapting a vertical one to draw heated water from a homemade project. Once again congrates,with help from people like yourself we can beat the big energy companys BONE


----------



## Hobartian

Hi Bone,

 I can confirm the heat exchanger was made from a standard propane tank.

I removed the base from the cylinder and drilled twelve two inch holes around the perimeter of each end ensuring that the holes were in alignment.    Because the ends of the cylinder are curved I needed to file the holes to an elliptical shape so the tubes would run parallel to the walls of the cylinder.   Be very careful welding propane cylinders as the steel seems to retain some residual gas.   I have found the best way is to flush the cylinder with water and after that deliberately introduce a flame into the cylinder while you are standing well away so that any fumes are burnt in a controlled way.        My heat exchanger has twelve tubes but probably eight would be sufficient.

I welded an extension piece on the outlet end of the HX for the purpose of collecting the hot gases and I pressure tested the cylinder with compressed air to check my welding. 

I would be interested to see some pictures of your finished project.


----------



## BONE

Hobartian,thank you very much for your time,my project is a down draft boiler,im going down the route of this type of heat exchanger,because they are readily available and easy to convert,but this is only the idea stage,getting it to fit and do the job efficiently will be another matter,steel is so expensive here,so you make do with what you can get. Thanks again.


----------

