# My first wood boiler, storage and data monitoring



## brack86svo (Aug 9, 2016)

When I decided to build a garage last year, I knew I needed to have radiant floor heat. Before that, I was heating the house with a Breckwell Big E that I had added a coil, to heat water for an air to water heat exchanger in my air handler. There is a thread somewhere on here of that project. I knew the pellet stove would not generate enough energy to also heat a 900 square foot concrete slab.

In March of this year I purchased and installed a Central Boiler Classic Edge 350. I plumbed it to the house, hot water heater and garage floor with no storage. I only needed to run the stove for about 2 weeks before it was warm enough to not need heat. In that 2 weeks I found very quickly, that I needed storage. The first night I heated the garage, the boiler ran great and burnt the entire load of wood. After the floor was up to temp, I would have a couple nights that the fire went out due to little to no heat load.

Against a good bit of what I read on this forum, I used home heating oil tanks for my storage. The system is open, and I used brand new tanks. The main reason for heating oil tanks, was that was all I could get to fit through the door to my basement, that actually had some decent volume, and was affordable after spending so much on the stove.








In that corner of the basement is the sump pump for the house, so if there is a leak, it should at least drain into the sump. The tanks are on legs about 6 inches off the ground, and have drains plumbed together into a valve that goes into the sump pit.

I used the top 2" npt ports of the tanks for all my connections. I made pipes for my return to the boiler and the returns from my heating loops.




The pipes for the return to the boiler is about 4" off the bottom of the tanks. The return pipes from my loops are about 12" from the bottom. My logic was that the water returning from the loops would still hold heat. Not sure that mattered at all but, that's how I did it.





Either end, the 2" pipe, is the line coming from the boiler, and the feed to the pumps. The 2" pipe was a nightmare to get leaks to stop, so I ended up switch it to one inch pipe. The pump on the right is the feed to the house. I had to switch that to the return side, as it kept losing prime somehow.

The first thing I noticed when I turned the pump on from the boiler, it created pressure in the tanks and bulged them. With the pump running, I am seeing about 5 psi. It took me a little while to figure out why, when it should have been obvious. The pump on the boiler is on the hot side, pushing water into the house. Pressure is created in order for the water to push back into the stove. As soon as the pump is turned off, the pressure goes away.

The tanks will be insulated with 2 part urethane 2lb foam. I will build forms around the tanks with plywood, and pour the foam in. There will be about 6" thick foam around the tanks. Here is a picture of small batches I was mixing and pouring under the tanks, to make sure I got good insulation on the bottom.
	

		
			
		

		
	






I will take the foam up to just near the fittings on top, then find a different way to insulate the tops. I want to be able to make changes, or fix leaks relatively easily.

I know the biggest thing with using these tanks, is going to be water treatment. As of right now, my nitrite levels are perfect, at least according to the test kit that came with the boiler but, my PH is 7. I going to add some sodium hydroxide to try to raise the PH to about 8 to 9.

Data monitoring will be done through a ControlByWed X300. The X300 will control my pumps based on set temperatures from the 8 sensors.

I don't want this to get anymore long winded. I love seeing peoples projects and builds, so I though I would add my own. I'm open to all questions and comments.


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## brack86svo (Aug 9, 2016)

Forgot a picture of my "control center". I run the stove and pumps off an APC 2200 ups with four AGM batteries. The main reason was to keep the pump for the garage running, and prevent a freezing situation.


Not sure why the picture rotates when I upload it.

I use the X300 to control what the pumps do during certain conditions. I can set it so that if the tank temperature drops below a set point, it will shut off the pump in the house, to keep from pulling heat back out of the water heater.
I currently have it setup with a probe drilled into the outer edge of my garage floor. If the floor gets below 40 degrees, the pump will kick on, and only circulate water through the outer loop. Once it reaches 70 degrees, the pump will shut back off. The garage thermostat can turn the pump on, and also open the 3 zone valves on my 4 loop manifold. I did not insulate the outer edge of the concrete for the garage. It was mainly oversight on my part when building it. Until the day comes that I have equipment there to dig back down to the footers, this solution, I'm hoping, will keep the water from freezing around the edge.


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## leon (Aug 9, 2016)

As long as I am waiting on a phone call from Honeywell I have a couple of questions;

You have Hydronic circulators not pumps. there is big difference.

Where is your vent line from the top of the tanks? It does not appear that you have a vent line coming through the roof with a U to vent excess pressure against the roof? You need a vent line.

The open system vent on your boiler is not enough for your plumbing.


YOU need one coming from the top of both tanks to the roof with a large U to allow the water pressure to vent through the roof.
If you have not done it yet add a few drops of Dawn Dish Soap to get rid of the air bubbles.
If you have not insulated the tanks yet hold off on that as the heat shedding is something you need to allow.


Why to do you want anything but a neutral PH????????????????????????????????????????????????????? You need a near neutral
PH with the tanks in the basement being full all the time.


Right now you have both circulators fighting with each and not creating a point of "no pressure change" as they are plumbed and you need to move one of them.

With your plumbing as it is now the water is not mixing and all the hot water is staying at the top of the tanks AND you are creating a huge amount of turbulence that will destroy your circulators.

You need to do much more work before you go any further.

Please in vest in  a copy of "Pumping Away" and "Classic Hydronics" written by Dan Holohan and available at Barnes and Noble or
www.dansbooks.com


if and when you move a circulator you can plumb in a dip tube in the two inch NPT fitting to near the base of the tank to keep the water from stratifying.


You also need a vacuum gauge for each circulator on the suction side of the flange disconnects and pressure gauge on the discharge side of the circulators.


Ideally the vent pipe should be at least 2 inches and plumbed into the top of the tanks to allow a zero pressure difference in both tanks and to eliminate any chance of the tanks rupturing or collapsing from a large pressure gradient.

You also need to keep the garage loop hot all the time as the lag time needed to heat the floor will be huge.


Please do not hate for asking but is it too late to move one tank to allow them to be plumbed in series as your system is fighting itself now as it is plumbed.

if you do that you can have flooded suction for the circulator and it will not be working as hard either.



You may also need several steel expansion tanks mounted in the ceiling joists in the basement to
create a stable 12 pounds of pressure for your system as your circulators are creating at least 18PSI and fighting each other because you have no point of pressure change the way the plumbing is now set up-the reason the tanks started to collapse on you. if you had a 2 inch vent to the roof they would not do that.

Ideally the single circulator or both circulators need to plumbed at the bottom to have flooded suction with a large isolation flange.

With a flooded suction piping system you could use one circulator and split the flow to your two zones provided you vent the tank to the roof line with a U elbow and screen set up to prevent icing up or plugging see below


You need need a rubber vent pipe boot for the pipe through roof. The pipe through the roof must at  least a foot in length to be above the roof, one 90 degree elbow, one short nipple nipple, and one more ninety degree elbow.


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## brack86svo (Aug 9, 2016)

Pardon my vernacular.

The vent line for the tanks is the line running back to the boiler. The boiler is an open system, and the highest point in the system.

Central boiler wants the PH level between 8 and 9. For the purposes of the warranty on the boiler, I want the water conditions exactly where Central boiler wants them to be.

From what I can find about a point of no pressure change, it seems to apply to closed systems. Can you please elaborate a little more on this.

The garage loop will depend on a demand for heat from the thermostat. I wouldn't want to constantly heat the floor, as the temperature would continue to climb.

Nothing about my system is closed, so I'm confused how I would need expansion tanks.


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## BoiledOver (Aug 9, 2016)

brack86svo said:


> Pardon my vernacular.
> 
> 
> Nothing about my system is closed, so I'm confused how I would need expansion tanks.



Your water volume will increase by approximately 4% when the water temperature is raised from 33F to 180F. That is a ballpark percentage and will never exceed 5% unless flashing to steam. A volume of 1,000 gallons x .04 = a 40 gallon increase.


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## leon (Aug 9, 2016)

brack86svo said:


> Pardon my vernacular.
> 
> 1. The vent line for the tanks is the line running back to the boiler. The boiler is an open system, and the highest point in the system.
> 
> ...




====================================================================================================

Hello brack86svo,


"Resistance" to water flow is what creates the pressure in a cool or heated hydronic system. Your circulators are pushing water through the pex and fitting and each and every foot of PEX and every fitting and foot of steel pipe is creating the resistance to flow.


number one: are you saying that the cool water return line to the boiler is the vent line????

number two: be sure to have boiler treatment on hand as your going to need it due to the airspace above the water line.

number three: the point of no pressure change applies to all hydronic systems either open or closed as it relates to the pressurised circulation of water. right now your circulators are fighting against each other and trying to create 12-18 PSI in the current plumbing connection that you have.

number four: your going to want to keep the slab some what warm all the time as it will take forever to heat up and by keeping the slab warm you will reduce the overall demand for heat as the slightly cooler water will be coming back to the boiler and storage.

number five: your water storage is "closed" and feeding water back and forth to the garage, the boiler, and your storage. The only open area is the boiler air space. that is why I said the tanks themselves need to be vented to atmosphere at the highest point in your system.

The water weight in the boiler itself is creating pressure into your basement storage tanks. Oil tanks are only good for one atmosphere in pressure 14.28 pounds psig.


Venting pressure from the top of these two tanks to a roof vent is the only safe way to do this with what you have.

Is it too late to think about putting the tanks in the garage and running a length of thermopex along the ground to the boiler for now and burying it later as heating season is only a few weeks away.
In that way one circulator can be pulling heat away from the boiler to storage and the other one can be used to heat your homes heating loops and the garage.

I am not trying to hinder you my friend, but the basic physics for hydronic heating and thermal expansion are your enemies here and I do not want to see you dealing with a ruptured set of tanks and no heat in your house.


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## brack86svo (Aug 9, 2016)

leon said:


> ====================================================================================================
> 
> Hello brack86svo,
> 
> ...



Yes, the only vent from the tanks is the return line to the boiler, and the boiler is vented.

Right now, the boiler is pushing water into the tanks. The garage loop circulator is on the supply side, and the house circulator is on the return side. If I run just the house and garage circulator, I have no pressure in the tanks. The only time I see pressure is when I run the boiler pump.

So you're saying that I need to have a vent coming from the tanks that reaches higher than the vent on top of the boiler itself, as that is the current highest point?

I have about 700 gallons of water storage between the tanks and boiler, so how would I add open expansion?


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## leon (Aug 9, 2016)

From page 116 from of Classic "Hydronics" written by Dan Holohan


"While were looking at old tanks, I want to mention what goes into sizing a compression tank. 
You have to consider these things:

1. The amount of water in the whole system

2. The difference in pressure  between the feed-valve setting and the relief valve setting 

3. And the Average water temperature of the system on the coldest day of the year."


===========================================================================


A gravity hot water system has expansion to the atmosphere via a roof vent as I described. The basement tanks are going to act as 
the boiler reservoir essentially and the tanks have to vented from the top UNLESS you hang a seventy gallon tank in the ceiling with pipe straps or a series of 7 15-gallon tanks in the ceiling joists cross connected with a common header pipe feeding all seven tanks with an "Airtrol fitting in each tank tapping that allows hot water and air bubbles to rise and cold water to drain back to the tanks. this gives you 70 gallons of expansion 

Short of that having a larger vertical steel expansion tank in the attic with a vent pipe through the roof may be your only other option.  


Your going to need a plumber that deals with gravity hot water heat or a B+G technical sales representative to come to your home to look at your current system as you may end up moving the two tanks to the garage using them as nurse tanks in series to the new boiler if you have the room in the garage for them.






I am not trying to spend your money I just want to help you.


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## maple1 (Aug 9, 2016)

I'm pretty sure oil tanks are not good for 14 psi. I would suggest that even 5 is too much, by a factor of about 2 or so.


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## brack86svo (Aug 9, 2016)

maple1 said:


> I'm pretty sure oil tanks are not good for 14 psi. I would suggest that even 5 is too much, by a factor of about 2 or so.



The 14 psi he was referring to is barometric pressure, I'm pretty sure anyway.

If I put an expansion tank higher than the boiler itself, wouldn't it just push the water out the top of the boiler?


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## maple1 (Aug 9, 2016)

Maybe. But we know very little about your system arrangement & layout. Where is all the extra water going now that gets made when your system goes from cold to hot?


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## brack86svo (Aug 9, 2016)

maple1 said:


> Maybe. But we know very little about your system arrangement & layout. Where is all the extra water going now that gets made when your system goes from cold to hot?



It would go into the boiler. The boiler has a vent pipe on top of it, and is the highest point in the system. From what I have found, every 1.8 degrees in temperature increase will result in an increase of 1.0002 in an open system. So if I have 700 gallons at 40 degrees, and heat it to 185 degrees, I should have about 712 gallons. I would think the storage tank of the wood boiler would be able to take on this expansion. The wood boiler has a 150 gallon storage tank, that is only to be filled to certain level due to expansion.

I'm not doubting the need for venting my storage tanks, I'm just trying to understand the need for expansion if the system is already vented to the atmosphere, and my expansion should only be 12 gallons, and any pressure from expansion would just get pushed out the vent of the boiler.


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## maple1 (Aug 10, 2016)

There might be issues, if the expansion from heat pushes out water, then the system cools some & the water level drops. That drop would create an empty space at the top of the boiler which may be larger than what the manufacturer intended (due to the significantly extra volume of water in the system), and create more corrosion potential in that empty space. I am thinking the increased back & forth due to the increased volume would pull more oxygen into the system, also increasing the corrosion potential. If you stay on top of the chemicals, it might help - but I think the empty space at the top would still be prone to corrosion. Have read lots of bad stories about some OWBs corroding out at/around the water line.

We also still don't know much more about other system details - such as elevation difference between the bottom of your tanks & the top of your boiler. But the fact that you bulged your tanks just from having your circ running (I think I read that right) would make me quite apprehensive.

Not sure I'll be able to add much more to this one.


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## brack86svo (Aug 10, 2016)

maple1 said:


> There might be issues, if the expansion from heat pushes out water, then the system cools some & the water level drops. That drop would create an empty space at the top of the boiler which may be larger than what the manufacturer intended (due to the significantly extra volume of water in the system), and create more corrosion potential in that empty space. I am thinking the increased back & forth due to the increased volume would pull more oxygen into the system, also increasing the corrosion potential. If you stay on top of the chemicals, it might help - but I think the empty space at the top would still be prone to corrosion. Have read lots of bad stories about some OWBs corroding out at/around the water line.
> 
> We also still don't know much more about other system details - such as elevation difference between the bottom of your tanks & the top of your boiler. But the fact that you bulged your tanks just from having your circ running (I think I read that right) would make me quite apprehensive.
> 
> Not sure I'll be able to add much more to this one.



The elevation difference is about 4 feet from the top of the tanks to the bottom of the boiler. I know I need to vent the tanks. The only thing that concerns me is, when the boiler circulator is running, wouldn't it just push water up the vent line to a certain point? This would cause low volume in the boiler and require more water to be added?

Here is a crude drawing of the boiler and tanks


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## warno (Aug 10, 2016)

You need to vent your tanks to equal height of the boiler vent or your water from your boiler will just push out the lower storage tank vent from gravity. So just run a piece of pex up to the same height or higher then your boilers vent and you're good. 

I know you said you bought the fuel oil tanks because they fit into the basement, my question is you couldn't find anywhere that had any type of pressure vessel tank (propane, air, etc.) That could fit at all? My only concern on your system is the thin walls of your fuel oil tanks rotting out in a few years. Even with proper maintained Chem levels the tank walks are still very thin. Especially if you use that foam insulation. You may get a small leak in the wall or bottom of your tank that you might not realize, then one day you have a soggy basement floor.

Not trying to beat you down just food for thought is all.


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## brack86svo (Aug 10, 2016)

warno said:


> You need to vent your tanks to equal height of the boiler vent or your water from your boiler will just push out the lower storage tank vent from gravity. So just run a piece of pex up to the same height or higher then your boilers vent and you're good.
> 
> I know you said you bought the fuel oil tanks because they fit into the basement, my question is you couldn't find anywhere that had any type of pressure vessel tank (propane, air, etc.) That could fit at all? My only concern on your system is the thin walls of your fuel oil tanks rotting out in a few years. Even with proper maintained Chem levels the tank walks are still very thin. Especially if you use that foam insulation. You may get a small leak in the wall or bottom of your tank that you might not realize, then one day you have a soggy basement floor.
> 
> Not trying to beat you down just food for thought is all.



From what info I have found, the boiler is made of 10 gauge. The tanks are made of 12 gauge. As long as I'm diligent with my chemicals, I should be able to get a few years or so out of them. The plan is to eventually add an outside entrance into the basement, and do two 500 gallon propane tanks. I will add a vent line, then see what happens with regards to expansion. Even at a 4% expansion, I think I will need about 30 gallons of space. I will just need to find a place that I can make room for the tank, that is higher than the lines for my loops, and lower than the vent on the boiler.


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## maple1 (Aug 10, 2016)

With 4 feet of elevation from top of tanks to bottom of boiler, then adding another 4 feet of height for each of the tanks & boiler (a guess), that would make about 5 psi of pressure at the bottoms of your storage tanks just from standing water with no added forces. I don't have an oil tank any more, but I'm pretty sure the stamp on it re. pressure was something like 2.5 psi? Could be wrong - but it doesn't take much pressure to pop such a tank, as has been seen with the bulge. There's likely some wiggle room in there, but I'd still be apprehensive..


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## Bob Rohr (Aug 10, 2016)

Do you have any piping or heat emitters above the boiler?  If so, that section will run at sub atmospheric conditions.  Here is an example of how that calculation works.

Also the PONPC is an open system is right where the air and water meet at the top of the boiler.

The Taco pumps should be rotated so the motor is not pointing up, to assure you have fluid at the bearing.


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## brack86svo (Aug 11, 2016)

Bob Rohr said:


> Do you have any piping or heat emitters above the boiler?  If so, that section will run at sub atmospheric conditions.  Here is an example of how that calculation works.
> 
> Also the PONPC is an open system is right where the air and water meet at the top of the boiler.
> 
> The Taco pumps should be rotated so the motor is not pointing up, to assure you have fluid at the bearing.



The boiler is the highest point, as in none of the loops go above the top of the boiler.

I did not know that about the circulators. I will turn that when I drain the system to add my vent and expansion tank.


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## brack86svo (Aug 12, 2016)

I'm having trouble figuring out what height to mount the expansion tank. since the tank will be straight through and be part of the vent line from the storage tanks, if I go too low below the water line in the boiler, it will just fill with water from the boiler and even itself out. If I go too high, the water would just come out of the vent on the boiler. Best I can come up with is mounting it horizontally with a small portion of the tank below the water line of the boiler. I figure at best, the top of the tank needs to be below the vent of the boiler.


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## maple1 (Aug 12, 2016)

I'm half in the dark here, having no experience with an open system - but my simple thinking has me asking why not simply put the expansion at the boiler vent? I'm not understanding why it needs to be plumbed into the top of storage. That would also help reduce or eliminate the corrosion-prone air space in the boiler - but would likely add some height & static pressure to the system, I guess. Or if not at the vent itself, then tied otherwise to the boiler.


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## brack86svo (Aug 12, 2016)

I though about that but, I would have to do some serious rigging to put it up on top of the boiler, and I don't want to make it an eye sore. I'm debating extending the vent up higher on the boiler, that way the expansion tank can be bottom positioned at the top of the cold water line, and still take on the expanding water, without overflowing the boiler.


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## hondaracer2oo4 (Aug 12, 2016)

Simply out of ignorance, could you tell me why it needs that vent tank at all? What is the difference in volume at 160 degree vs 180(the boiler temp differential settings)? Can be more than a few gallons I would think. Couldnt you just let the boiler blow out the extra water from the top vent on the boiler the first time it fires, then it would just run with that amount of water. If you cooled the boiler down to 140 or less for some reason you might have to add some water.


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## leon (Aug 12, 2016)

Please call someone from B+G or Taco and ask to 
have a field representative come to your place 
to look at your system.

They deal with large volumes of water for hydronic storage in 
heating and cooling as a business for large buildings and skyscrapers.

At most you may have to move the tanks to the garage 
and use them to buffer the water storage temperature 
in the boiler to avoid further damage to the tanks.

If you put the tanks in the garage they will be higher 
in elevation and be subject less pressure from the 
water weight in the boiler. 

You can always have a vent stack with an upside down U to 
vent teeing both tanks together with one vertical pipe

A steel expansion tank must have a sealed system storage to 
work properly with a sealed air cushion above the water line to allow
the air bubbles to migrate to the air pocket and slowly dissolve in the water column.


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## Bob Rohr (Aug 12, 2016)

How many gallons total?  You need to calculate the expansion volume for the fill water temperature, to max temp, maybe 60- 190F operating range.  You cannot calculate from 160- 190, if it goes off and drains to ambient temperature you will have a low water condition in the boiler.  Water both expands and contracts.

How much expansion space is in the boiler itself, generally they have space for expansion for at least the volume of the boiler itself.  Adding those buffer tanks may require additional expansion room.

The Wessel Tank website has a sizer for calculating tank volume, the boiler manufacturer should know the expansion available in the unit.


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## maple1 (Aug 12, 2016)

I think its in the 15 gallon ballpark, of expansion. Not a whole lot, but its about 10% of boiler volume.


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## warno (Aug 12, 2016)

I ran my home built boiler(120 gallon)  last year with temp swings from 180-150. My system is open. I filled the boiler to just under "full" then fired it up. I let the boiler heat up and burp out the expanded water from the vent line. After a few days all the expanding that would be going on just rose and fell in the boiler tank, no more water came out. When I opened the maintenance cover the water was just under where it started. 

I should add that I designed a "bubble" into the top of my boiler tank to avoid the rust ring in the majority of the boiler tank. So my rust ring could actually rot through its loaction and I could still run just fine.


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## brack86svo (Aug 13, 2016)

Not sure on how much expansion they factor in. I know when I filled the boiler in March (temp in the 30's), I filled it 1" below the full line as they recommend. When it is at full temp, it is right at the full line. I will email central boiler and see if they can tell me. I was thinking about sticking my scope down in the vent just to see what exactly it looks like in there, at least to see the expansion space. The plan right now is to add a 26 gallon tank for expansion. Worst that will happen, the water will expand too much and push out the vent on the boiler.

I will try to reach out to a Taco rep to see if they can advise me based on the info I can give them. I don't have any way that I can put the tanks in the garage. I had already considered that as an option but, the garage space is far too valuable to sacrifice, whereas the basement, which leaks slightly during prolonged periods of heavy rain, is no more than a storage area.

I appreciate all the input. I may not take all the advice. I will however try to adapt it to what I can accomplish.


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## warno (Aug 14, 2016)

If you can measure your remaininh space in your  water jacket on the boiler you can do the math to figure out how many gallons to expanded to your "full" line. 

If you are calling Central Boiler anyway it may be beneficial to ask them their advice on your project. Worse case they say they don't recommend it and then all your out is the breath it took to ask. 

Good luck to you.


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## brack86svo (Oct 23, 2016)

So I've ran the stove and heated the tanks. Everything so far is working really well. No pressure in the tanks now with the vent line running out and up through the garage roof.

The issue I am running into now is..... The boiler will go into idle before the tanks are up to temperature. I set the water temperature on the stove to 190, and the most I could get the tanks to was 180. The gauge on the line coming in from the boiler is reading 180 to 190, water temp out of the tanks to my loop is reading 170 to 180. The reading I am getting from the sensors hooked to my X300 confirm this 170 to 180 temperature. So the tanks seem to get to about 150, boiler at rated temp, then goes into idle for awhile and cycles back and forth till the tanks get up to about 180.
The only thing I can come up with is, the circulator is too small. I'm running a 007 on the boiler. Is there a calculation based on gallons per minute that I should make for the circulator when heating that much water? Ideally, I at least don't want the boiler to idle until the tanks are up to temperature.


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## jebatty (Oct 24, 2016)

brack86svo said:


> The issue I am running into now is.....


 A "simple" problem, likely, and also relatively simple to solve, maybe. It's all about the math. BtuH moving through pipe = deltaT x gpm x 500. I will assume that you have 1-1/4" inside diameter supply and return pipe. If your pipe diameter is smaller, you have a significant problem. If it is larger, your problem may be less. 

I will assume you have flow rate of about 12 gpm, that being the recommended maximum flow rate with 1-1/4" pipe. Do you know what your flow rate is? Do you know what your pump head is at 12 gpm? The 007 pump curve will tell you the flow rate if you know the pump head. Pump head can estimated/calculated based on pipe size, pipe length including fitting equivalents, and flow rate. The 007 pump curve shows that 007 will move 12 gpm at pump head = about 7 feet. If the pump head is > 7 feet, less flow; if < 7 feet more flow. What is your pump head at 12 gpm?

Assume maximum flow rate of 12 gpm. Assume deltaT = 20F. Then btuH that can be moved = 20 x 12 x 500 = 120,000. Any output of your boiler > 120,000 btuH will result in the boiler having rising temperature because all output is not being moved out of the boiler. Temperature will rise to the idle point, then boiler water will gradually cool to the restart point, repeat.

Now assume deltaT = 30F. Same calculation: 30 x 12 x 500 = 180,000 btuH. This looks close to your described situation, 150F water coming back to the boiler. But you still experience idling cycles, particularly as return temperature increases above 150F.

The solution is either to increase your flow rate which might not be easy, or to reduce your boiler output as return water temperature rises above about 150F. You can reduce boiler output by making sure that when you load the boiler you have plenty of storage capacity to absorb the boiler output as the wood load burns down. And as the wood load burns down, boiler output falls, and at 12 gpm and with deltaT falling below 30F you still can move the boiler output without idling.

More to the point. Your boiler has a rated output of 170,000 btuH. This would likely be high burn maximum output, with output falling as the wood load burns down. The problem is now clear. Your system will not move sufficient water at deltaT < 30F to handle the boiler output. The solution is not to overload the boiler so that boiler output is falling as return temp reaches 140-150F and the full reducing boiler output can be moved to storage without idling.

With care in loading your boiler you may be able to raise storage to your desired maximum temperature without boiler idling. Do a search on this forum for "weighed wood burns" and you will find an extensive discussion on how to do this.


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## brack86svo (Oct 24, 2016)

My piping to and from the boiler is 1" and is about 60' round trip between what is in the house to the tanks and buried piping. The flow head I calculated out to be 7.24. I don't know what to add to my calculation for the thermostatic valve that Central Boiler includes with the system, so my figure may be off. Based on what I did get though, 007 is the right circulator.


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## jebatty (Oct 24, 2016)

Is the piping actually 1" inside diameter? If so, I calculate close to yours at 12 gpm: 60 feet with 1" steel pipe = 7.22' of head; about 7.6' feet of head for plastic pipe. But note what this means on btuh carrying capacity: 180,000 btuh at 30F deltaT, 120,000 btuh at 20F deltaT, 90,000 btuh at 15F deltaT. 

Your boiler is rated at 170,000 btuh and at the temperatures you mentioned, 12 gpm may not move your boiler btus at higher outputs, which means idling.


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## jebatty (Oct 24, 2016)

The 007 pump curve shows closer to 11 gpm at 7.22' of head: 165,000 btuh at 30F deltaT, 110,000 btuh at 20F deltaT, and 82,500 btuh at 15F deltaT. And if the pump head is greater, the numbers are less.

Edit: On my second install attempt on my Tarm, I used 1" steel pipe. Too small for boiler output, and I had a problem similar to yours.


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## brack86svo (Oct 24, 2016)

It's all 1" pex, then the connections at the tanks are 1" black pipe. Seems like the max GPM for 1" pex is about 7.5. My thermopex is under concrete, so changing the size at this point isn't an option. I was just hoping to move the water from the boiler to tanks at a higher volume, doesn't seem like that will be feasible with the 1" thermopex.


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## Nofossil (Oct 24, 2016)

I may have missed this, but can you set up the boiler circ to pull cool water from the bottom of storage rather than pushing hot water into the top? It *might* help to use a Viridian circ set up to vary the speed to give you the temp that you want going into storage. That way the actual flow rate will be faster when the boiler is producing a lot of heat, and slower when it's not. It would also compensate for the situation where you're returning hotter water to the boiler (when you don't have much stratification in storage) - it will run faster to keep the boiler outlet temp from getting too high, which should reduce the chance of the boiler idling.

The whole 'pumping away from the point of no pressure change' concept is not carved in a sacred tablet carried down from a mountain somewhere. It's a design concept that addresses two things: First, that scheme does a better job extracting air from the system as bubbles come out of water more effectively at lower pressure. Probably not a big concern in your situation.

The second issue is cavitation. The boiling point of water drops as pressure drops. If you have a big circulator and you're running high temperatures, you can get a low enough pressure on the inlet side so that the water will flash to steam, causing cavitation and severe wear on the circulator impeller. Typically a concern with larger systems, though some folks here have managed to produce this effect in residential installations.

This is a design consideration on closed systems, where you typically have an expansion tank and air separator, and you'd ideally place the circulator just downstream from them. On an open system, it's a bit different. To reduce cavitation risk, you'd ideally have your circulators lower in the system (as you do), and have them on the cool leg rather than the hot leg.

If you decide to go with the Viridian as I mentioned above, it would be ideal to place the temp sensor near the boiler outlet, even if the circ is in the basement.


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## brack86svo (Oct 24, 2016)

This is a completely open system, so I'm not sure that I can put the circulator on the return side. I don't know if the water would go back into the storage tanks if it were run in that configuration. The stove itself, is setup exactly how Central boiler recommends.

Right now, the temperature in the tanks is virtually even from top to bottom. So is it possible the issue I may be having is the return water from my heating loops is piped to the bottom of tanks, causing the water to mix too much, vs having the cold water stay to the bottom?


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## Nofossil (Oct 24, 2016)

Without a more detailed plumbing diagram I wouldn't even hazard a guess, though if you pull water out of an otherwise sealed tank, more water has to be drawn in to replace it. An open system isn't *that* different from a closed system in that respect.

The lack of stratification may also be caused by the way the plumbing is configured. Incoming hot water is injected straight downwards. With sufficient velocity, that can result in pretty complete mixing from the get-go. That's a reason why the Viridian might help - most of the time it will be running at less than full speed, resulting in less mixing in storage.

Can you take some readings during the charge and discharge cycles - maybe top / middle / bottom - and see if you get mixing during charge, discharge, or both?


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## brack86svo (Oct 24, 2016)

I don't have any way to get to the middle of the tanks since I foamed them in.

When I first fire the boiler, the water is hot on top, cold on bottom, and stays that way till the house circulator kicks in. It kicks in when the top of the tanks gets to about 120*. At this point, the water temperature in the tanks starts to mix. By the time the top of tanks reach 140*, the bottoms are right about the same.

I made some changes to the X300 to see if it helps. I set it up so the house circulator kicks off at 120* but, it won't kick back in till I recharge the tanks, and the bottom reaches 160*. I'm hoping this will pull more of the cold water off the bottom, and keep the boiler from going into idle.

I will try to monitor everything the next time I charge the tanks and see if made any improvement.


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## maple1 (Oct 24, 2016)

What do you have for zones & a house circ?


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## brack86svo (Oct 24, 2016)

I have two zones. One is radiant heat in the floor of the garage. I haven't even run that yet, as it hasn't been cold enough. The other is the house. It has a 007 that pumps through a sidearm and then a plate exchanger for the water heater. From there it goes through  a heat exchanger in my air plenum to heat the house.


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## maple1 (Oct 24, 2016)

If you could slow that load flow down you'd likely see better storage action. Switching to an Alpha circ was one of the best things I ever did. I might also consider running to the plenum exchanger first, or breaking them into separate zones.


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## jebatty (Oct 25, 2016)

I feel the frustration in the OP's situation. I was there when I first set up my Tarm, using 3 oil tanks in open storage with a 140,000 btuH rated boiler and first 3/4" and then 1" steel pipe and a 007 circulator. Very similar issues.

Slowing down the flow may help with less mixing and more stratification in storage but even with cooler return water the idling issue may be worse. Typical 1" pex is 0.875 inside diameter, not 1", and I assume Thermopex is the same. Flow may be about 8 gpm, assuming head is based only on 60' of pipe, and it likely is less ("It has a 007 that pumps through a sidearm and then a plate exchanger for the water heater. From there it goes through a heat exchanger in my air plenum to heat the house.") At 8 gpm btuH capacity is only 120,000 at deltaT=30, much less than the 170,000 btuH rating of the boiler. 

Also, the two oil tanks for storage probably have a capacity of about 275 gal each, 550 gal total. This is fairly minimal storage for a 170,000 btuH boiler. Assuming minimum usable water temperature is 120F, maximum storage capacity from 120F to 185F is about 300,000 btus. To prevent idling some very careful boiler loading may be required to keep both the burn rate and total burn output on the low side of the boiler rating. This may cause other problems for the boiler, as best boiler operation in my experience is allowing a boiler to operate at maximum burn rate through the burn, meaning high burn on loading and then gradually reducing output as the wood load burns down. 

I would like to find an easy solution to the problems in this situation, but that easy solution escapes me at this point.


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## maple1 (Oct 25, 2016)

One other thing is likely raising the temp your house/load circ kicks in at. I can't see you getting much heat out of the water when it is only 120, especially with a plenum HX - so the load circ at that point is only serving to mix your storage & mess up stratification. I would try raising that to the 140-150 area - along with maybe trying to slow load flow. But you likely can't do much on that end with a 007. Plus when winter really hits, you might need some of that flow back to keep your house warm - without knowing how the plenum HX performs as is. Which would be where having it before your DHW - or separate loops - would come into play.

You might be stuck with the idling issue with the underground piping you have - balancing wood loads will likely be key.


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## brack86svo (Oct 25, 2016)

I know the heat exchanger will still put out good heat below 120. The water coil I had installed in my pellet stove would drop down to near 100* and I had still had ok heat coming from the vents. I picked 120 since that's what we set the water heater to, and I wanted to make sure I didn't end up somehow pulling heat from that.

Sounds like in the long run, I may need more storage. My options are limited unless I put some sort of exterior access into the basement.

Either way, I'm better off now with storage, than I was without. I have not needed to heat the house yet, so just heating the DHW, the charge lasts about a week before it's below 120*. I'm going to try recharging the tanks next time without turning on the house circulator, and see if charges any better.


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## maple1 (Oct 25, 2016)

One more quick one.

I have heated my DHW all summer from storage, a couple of times now. The first tries at that, while I still had a 15-58 3 speed load circ, were pretty disappointing because it messed up my stratification too quick. Just flowed too much. I could only go maybe 2-3 days before needing to fire again. The situation was made worse because I only had a sidearm for a HX. I added a FPHX to the sidearm (and a small B&G Ecocirc on the DHW side of the HXs), and swapped the 15-58 for the Alpha which allowed me to throttle the flow on that circuit down to minimal (I also slowed my baseboard zone flows). Not sure what it actually is, but the digital readout on the circ says 1gpm when just the DHW zone is flowing. I could now go a week between firings, and the stratification remains. During that exercise, I also discovered that the 15-58 was also pulling some flow through the now-cooled boiler - also compounding things. Don't think it was a lot (which is why I didn't realize it was happening for quite a while), but it didn't help anything.

So my lessons learned from all that - an Alpha circ is awesome [HIGHLY RECOMMENDED] for multi-zone loads using a single circ (likely also for any system with a single load circ), and heating DHW all summer with wood might not be worth the hassles & extra component costs of doing it and should maybe be down on the priority list a bit when planning a system. (I have used my electric elements for it the past 2 summers, even with what is now a pretty good wood heating setup for it).

[I also ballpark figured that DHW BTU requirements are about 1/30 of my house heating BTU requirements, so don't see the need to priority it with an adequately sized DHW tank - random tidbit.]

(Guess that wasn't so quick....)


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## Nofossil (Oct 25, 2016)

Spot on. When charging DHW from storage (I have an indirect DHW tank with an internal finned coil) I run the charging circ at 10%, which is probably less than 1gpm. DHW recovery is a tad longer, but it does wonders for stratification and really extends the useful life of storage.

In my case I'm using a 007 with a variable speed control. I'd use an Alpha, but the US versions don't provide an external speed input :-(


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## brack86svo (Oct 25, 2016)

maple1 said:


> One more quick one.
> 
> I have heated my DHW all summer from storage....



So you run the Alpha through your DHW exchangers, then through your baseboard at the 1 GPM? I don't have a zone valve to separate my DHW from my heat exchanger in the plenum but, I'm not really sending much heat into the house if the blower isn't on, just some radiant into the plenum.

I probably will not separate the DHW and house heat into separate zones this year, since I don't want to drain the system down but, I have valves at the crics, so I may order that pump and play with the flow to see what I can get to work.


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## maple1 (Oct 25, 2016)

brack86svo said:


> So you run the Alpha through your DHW exchangers, then through your baseboard at the 1 GPM? I don't have a zone valve to separate my DHW from my heat exchanger in the plenum but, I'm not really sending much heat into the house if the blower isn't on, just some radiant into the plenum.
> 
> I probably will not separate the DHW and house heat into separate zones this year, since I don't want to drain the system down but, I have valves at the crics, so I may order that pump and play with the flow to see what I can get to work.



The baseboards are on 4 other separate zones - so as they open up, the pump pumps more. Not sure now that I think of it what my baseboard flow might be. Guessing 2-3 gpm? Also a bit suspicious of accuracy of the Alpha display, but not suspicious enough to try to measure my flows otherwise. My baseboard zone flows also get aided some by convective flow (the upstairs ones at least), which also might throw the pump display off a bit. Just so happened by chance that all of my zones ended up with areas needing the most heat being the first in the zones (and ones not needing a lot at the ends), so if the water in the rads is cooler at the ends of the zones, it all seems to work out anyway. Or maybe the guy who designed it 20 years ago really nailed things - seems he generously oversized my baseboard too, which I am quiet grateful for now with the changes I made since.


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## brack86svo (Oct 25, 2016)

I was reading a thread specific to this pump, and I think I may go for two of them. I'll use one for the heat in house, and one out at the boiler itself. I'm thinking it may help for the stages at which the thermostatic valve for the boiler opens and closes based on returning water temperature.

Thanks for the feedback


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## taylorfarms (Oct 26, 2016)

I would be looking for a heat exchanger or coil for your tanks, to separate the boiler from the tanks, relieving the gravity "pressure" on your tanks, and in the event that a tank ruptures your boiler does not run dry.  also kinda does away with the issues of venting levels


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