# Hot room in Green room



## byQ (Sep 12, 2013)

Well, I'm building two hot rooms to collect the sun's radiation - passive solar construction technique. I built up 2 rows of narrow cinder blocks. I got to work on my new found masonry skills.  I only did 2 rows for now so I can get the insulation ready for the main slab concrete pour. I'll finish these rooms when the house has a roof and walls. The white styrofoam blocks seen are insulated concrete forms (for outer wall construction).

These hot rooms are about 5'x15' and 5'x13' or 140 sq feet in a ~1520 sq foot house (40.5' x 32.5'). I hope they work. By work I mean I hope they create enough btu's to cut my wood usage by half. I'm installing five 3'x6' south facing windows, and painting the insides of these hot rooms black for maximum heat absorption. But I don't know how much heat they will collect on a sunny winter's day.

It will be interesting to see how well they work. I didn't do any calculations but am going by feel. The cinder blocks are 3.5 inches wide. After putting on a stucco coat, inner and outer, they should be about 4+ inches thick. Too thin and the wall won't have enough thermal mass to hold much of the sun's radiation. Too thick and the wall will hold the radiation but won't pass it on into the outer wall (and thus into the living space).

I got a good deal on the 3'x6' windows before I found out they weren't shatter proof (tempered glass). I learned that non-tempered glass must be 18" above the floor, oops. I planned on installing windows 4" to 6" above the floor. What to do? I lowered the floors in these hot rooms to compensate. The hot room slab's will be 10" to 12" lower than the main house slab (which will be a couple inches below the top cinder block in the picture). Well do you think it will work? And how well?


----------



## woodgeek (Sep 13, 2013)

I'd suggest you do a little more research.  A lot of passive solar work done by 'feel' in the 70s really didn't work well at all.  You don't want to repeat the same mistakes from 40 years ago.

1. Superinsulation (and airsealing) with a small amount of passive solar gain is great (and does not require a huge dedicated thermal mass).

http://www.greenbuildingadvisor.com...lar-versus-superinsulation-30-year-old-debate

2. Passive collectors (windows) are great at shedding heat at night, so you need to think on a 'gain/loss or profit basis'.  Either you need fancy expensive windows, or thermal curtains that you are now on the hook to open and close every day you live there, or you can separate the collector from the storage. You might want to consider building an unheated sunroom/sunporch with a LOW thermal mass, and insulation between the room and the house.  That way it will heat up quick in the winter on sunny days, you can open the doors to let the heat into the house, and then when the sun goes down, just close the door.  Any heat out there when the doors are closed will be stranded and lost (so low thermal mass is better).

This sort of solution can be improved by:
--adding a thermostat controlled fan to blow the air into the house when the space heats up, automatically.
--you can avoid overheating your house in the spring and fall by leaving the door closed or fan off....control!
--make enough openable windows in the sunspace so you can keep it from being an oven in the summer, and you have a great space for starting plants, sitting in the sun, etc.

Also, surfaces don't have to be black black.  Anything dark will be fine.

Gary Reysa at http://www.builditsolar.com/ is a member here.  He can tell you anything you need to know.


----------



## btuser (Sep 13, 2013)

Go for the super-insulation.  It's the best thing ever.


----------



## Seasoned Oak (Sep 13, 2013)

The sun provides a tremendous amount of heat during the day ,but those big windows give most of it back during the long night. I have partially solved this by allowing the sun heated air into the main house during the day through my front door which is between the sun room and the main house. At night i simply close the door once the sun room get cool. It works so well i can go about 12+ hours on solar alone on a sunny winter day. If my house were better insulated it may go much more.


----------



## Seasoned Oak (Sep 13, 2013)

Seems the right recipe is some solar,lots of insulation and a wood stove.


----------



## GaryGary (Sep 13, 2013)

Hi,
Looks like a really interesting project.

I'm a big fan of low thermal mass sunspaces  (LTMS) for space heating.

The basic idea is that you you have an attached sunspace that is optimized for collecting heat and sending it to the house.  During the day when the sun is shining, the sunspace makes a lot of heat and a blower moves the heat to the house.  At night when the heat loss would be high, the sunspace is shut off from the house and just goes cold. 
Optimizing the sunspace for producing house heat consists of: 1) Lots of glazing angled for good winter heat collection - preferably double glazed; good absorbing (dark) surfaces for the walls and floor;  2) all walls, floors and ceilings that are not glazed are insulated to reduce heat loss,  3) all the surfaces that the sun shines on are low mass so that the solar heat goes into heating the air and then the house, not into heating the sunspace mass, and 4) a good fan or blower and duct system to move the heated air from the peak of the sunspace into the house as fast as the heat is produced.

As long as the fan/duct system that moves heat from the sunspace to the house is sized correctly, the sunspace can be comfortable to be in (that is, not overheated) because the heat is being removed as fast as the sunspace makes it.  This takes a pretty good fan/duct system -- it needs to move air about about 3 cfm per sqft of glazing to keep up with the sunspace heat production.

Good summer ventilation is also needed if you want to use the space in the summer -- probably along with some shade cloth.

To me, the LTMS is a really nice combination of adding useful space to the house that can be used for all sorts of things and at the same time getting a lot of good space heating.
Downsides are that you can't grow plants in an LTMS as it goes cold at night, and if the sunspace is large and the house is really well insulated, the sunspace can overheat the house -- this can be addressed by adding storage, but for most cases, the house will have enough mass to store the heat the sunspace can produce.

If designed correctly, they are as efficient at space heating as good commercial solar collectors with the same glazed area.

I did a whole section on this, including a pretty careful test of heat output of a test low thermal mass sunspace.  Also several folks contributed detailed descriptions of their low thermal mass sunspaces.
http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm#LowMassSS

We are doing an article for Home Power that will be out this winter on low thermal mass sunspaces -- it basically has most of the stuff in the section linked to above in a nice, easy  to digest format.

Gary


----------



## byQ (Sep 13, 2013)

Thanks for the feedback. No fan or ductwork will be used just natural air cyclying from cold to hot.  The house is small and open. I think a combination of good insulation and solar gain is what I'm after. And modern house construction should be using both of these concepts. I'm pretty well insulated - ICF walls and 5" rigid board under the slab. The slabs in the hotrooms are also insulated on every side but the top. I'm going to do some extra rigid board insulation in the ceiling, too. I will probably put 4 openable vents in each hot room - 2 high and 2 low to let natural air cycling occur.

Most thermal shutters seem to be to big and bulky. But pull-down tight fitting insulated curtains are reasonable - maybe 2 seperated by a 1" space per window. I don't mind dedicating 5 minutes a day to this chore. I've read some of those 70's book on passive solar gain, and some of the ideas are good. But ya some were carried to extremes.

I think I will put dark grey/black natural slate/rock on the walls and floors. It will look good and is functional. Seasoned Oak I'll never install a wood stove in any house/cabin I live in since I will have the skills and knowledge to build masonry heaters which are superior heating devices. Why wouldn't I want the best? Just because most people take the well-worn same beaten path as everyone else doesn't mean I have to. And I will be able to build these superior heating device(s) at the cost of a mid-priced wood stove.


----------



## DevilsBrew (Sep 13, 2013)

I also have experience with a sunroom.  The room evolved to become our living space.  There were crank windows, french doors, and a fireplace to regulate the temperature.  Another use for the room was to extend the season for plants.  I loved the sunroom so much that I wish I had a passive solar glass house to live in.


----------



## byQ (Sep 13, 2013)

David & Geek, thanks for the links - interesting reading.


----------



## DevilsBrew (Sep 13, 2013)

What is the update on your masonry heater build?


----------



## byQ (Sep 14, 2013)

* What is the update on your masonry heater build?*

DB, Still working on building the house. I'll probably be able to do something with the masonry heater next spring. I'm going to attend a masonry heater build in Las Vegas, NV, in the spring. And try to attend a masonry heater workshop in Northern Minnesota in the winter at Northhouse.org. Northhouse has a rocket heater workshop, too. Two skilled masonry heater builders are starting to explore building rocket heaters/stoves.

I've been trying to figure out what size contraflow masonry heater to build. The plans I have have 2 contraflows, a small one 36" x 24" x 6' (36 ft3), and a large one 48" x 36" x 7' (84 ft3). I'm going for something in the middle say  42" x 30" x 6' (52.5 ft3). I've learned that MH size isn't that important in terms of heating. If you have a big heater and want less heat you just burn less firewood. The MH doors I got such a great deal on are too big for a small MH. Oh well, I'ld rather have a firebox I can get 18" pieces of firewood in instead of 14" to 16" pieces.

I've altered my house design to accommodate a medium sized masonry heater by increasing the house volume - 1) cathedral ceiling, and 2) upstairs bedroom/loft (+325 sq ft). Might as well give the MH something to heat. And I've decided to go with a refined organic look - 1' green marble tile on the outside of the MH and maybe a natural brown field stone hearth (horizontal and vertical). The MH will look like a large bush - a burning bush!




I'm going for a MH about this size with a small bench and an oven, but it will be green instead of red brick. And mine will have a bigger double door.  I'll use red brick, but on it's side (facing method). Than I'll mortar/mesh and use 1 foot marble tiles to finish.


----------



## Seasoned Oak (Sep 14, 2013)

byQ said:


> Seasoned Oak I'll never install a wood stove in any house/cabin I live in since I will have the skills and knowledge to build masonry heaters which are superior heating devices. Why wouldn't I want the best? Just because most people take the well-worn same beaten path as everyone else doesn't mean I have to. And I will be able to build these superior heating device(s) at the cost of a mid-priced wood stove.


Most people take the well worn path of a wood stove No1 because it works and No 2. Probably 99 of those wood stove users have neither the cash to buy one or the time and skills,space or desire to build one. Its the law of diminished returns, if a wood stove is 85 % efficient and your MH is 90% how much did you pay for that 5% and is it worth it?   You could say a fuel cell car is a superior trans.device as well but you wont get 99.9% of the population to pay 100K to find out.


----------



## byQ (Sep 15, 2013)

_Most people take the well worn path of a wood stove No1 because it works and No 2. Probably 99 of those wood stove users have neither the cash to buy one or the time and skills,space or desire to build one. Its the law of diminished returns, if a wood stove is 85 % efficient and your MH is 90% how much did you pay for that 5% and is it worth it?   You could say a fuel cell car is a superior trans.device as well but you wont get 99.9% of the population to pay 100K to find out._

I guess sometimes I like to take a harder path just because I can. Even though cost-wise, a masonry heater won't be that much (~$1200) it will take a lot of personal time and learning. But I am fascinated by mass heaters and enjoy the challenge of attempting to build one.


----------



## woodgeek (Sep 15, 2013)

The other issue, of course, is that MHs and superinsulated houses are not really compatible.  A right-sized MH might be the 'ultimate' wood heating appliance for traditional construction, but with the lower heat loads of a 'modern' efficient house, even in Idaho, a MH might consistently overheat the place unless you make it so small that it works more like a stove anyway.

What I'm getting here is that you are building your own house, using your own plans, learning everything you need to know as you go.  Great.  It seems you have set a goal of heating entirely with wood, and using 'half' as much wood as a typical neighbor with the same sized house, through a combination of three technologies: passive solar technology, superinsulation and high eff masonry heater tech.

We are trying to tell you is that instead of learning about and juggling three complex technologies....solar, superinsulation and MH, you could instead just go for the superinsulation, skip the other two, and get wood usage that was 75% less than a typical neighbor, exceeding your goal.  A reasonably superinsulated 1500 sq ft house, say to **half** the insulation levels of a Passive house, 2 BTU/sqft/HDD, would required 2*1500*8000 = 24 Million BTU per year, and much of that would come from appliances, so you would need <1.5 cords of softwood per year to heat the place, tops.  The natural cooling time of the house (due to its thermal mass) would be longer than that of a masonry heater, so you would get equal (awesome) comfort from a MH and a small cheap stove doing ~2 burns a day, and the latter would get you better 'control' and faster warm up.  If you got tired of kindling a couple fires a day from scratch, you could heat the place with two electric space heaters for <$1000/yr, or a single minisplit for <$400/yr.  Or heck, a small cat stove you could throttle down and run continuously, like a Woodstock Fireview would save you a bundle on kindling.

So, from my point of view, you are not building an eff house that uses half as much wood as a house should.  You are instead building a house with 2x the heating need of the current 2013 best-practice house, and thus creating a heating need that you will then try to bandaid over with two other things you are fascinated with, passive solar and MHs.  For the same amount of learning/building effort and cost, you could go for superinsulated walls, either thick double stud and (cheap) cellulose or conventional 2x6 framing + exterior foam (with cheap recycled foambaord), with careful airsealing, using blower-door tests before the drywall goes in.

The basic idea of a low-cost, optimal superinsualted house is called the 'pretty good house' and there is a ton of info online:
http://www.greenbuildingadvisor.com...ng-blog/regional-variations-pretty-good-house


----------



## Seasoned Oak (Sep 15, 2013)

Im fascinated by everything your doing there byQ so ill be following this thread and your progress. Keep in mind that as your solar gain and the insulation levels go up, the size of your MH and any other kind of heater may have to go down. As WG said if your house loses heat slower than the the MH is pumping it out you may have a problem. Plus you have the thermal storage to factor in as well,could be tricky. You may wind up getting most of you heat from the solar.


----------



## GaryGary (Sep 15, 2013)

Here is a superinsulated home with an MH and some passive solar that appears to be working OK.

http://www.builditsolar.com/Projects/SolarHomes/SchoolHouseRetrofit/Main.htm

I'm sure Gordon would be happy to answer questions about how the combination is working for him.

Gary


----------



## begreen (Sep 15, 2013)

Woodgeek brings up a very good point. It would be worthwhile investing in a plan review. Especially consider getting a heating and cooling load engineering analysis before casting decisions in stone and cement. Wise decisions made now could prevent expensive remedies later on.


----------



## woodgeek (Sep 15, 2013)

GaryGary said:


> Here is a superinsulated home with an MH and some passive solar that appears to be working OK.
> 
> http://www.builditsolar.com/Projects/SolarHomes/SchoolHouseRetrofit/Main.htm
> 
> ...



Nice project.  I noted that he designed the MH for 1 fire per day, and an average output of ~10 kBTU/h, and he has a huge amount of thermal mass in the house (which helps avoid overheating).


----------



## Seasoned Oak (Sep 15, 2013)

Im, tempted to try a little thermal mass in close proximity to my stove as im still finishing the stove room. It gets terribly  hot in there in winter mid 90s,with the stove on low,makes the room pretty much uninhabitable. Other than checkin on the stove i dont spend much time in there. Perhaps something to siphon some of that heat off for later. Was also thinking of some type of disguised water container, but probably a lot of stone surround is the ticket.


----------



## woodgeek (Sep 15, 2013)

the trick with thermal mass is either a modest amount of mass with a large temp swing, or a large mass with a small swing.  And the rate of heat transerf in and out of the store has to be 'right'.  Two things work well....(1) in a masonry heater a 'modest mass' heats up a good deal, and (2) in your house the entire house swings up and down a small amount and is VERY massive.  In a SS stove, the mass is smaller than an MH, but the swing is a little bigger, and the effect is worthwhile, but not as great as with a MH.  Water is tough, unless you are circulating to a store and some hydronic radiation.


----------



## Seasoned Oak (Sep 15, 2013)

I have to build a finished wall around the back and sides of the stove so im thinking 4" cement block with stacked natural slate stone against the block.Not sure if i should fill the block voids or not. I figure about 1-2 ton + when finished. Could be more as the slate cube is 2 ton alone but i dont think ill need it all.
Would this qualify as the modest mass with the large temp swing?


----------



## woodgeek (Sep 15, 2013)

I think it would be a modest mass with a small temp swing.  How much do you expect the mass to heat up from a single burn? 20°F, 40°F?  How long will it take to release that heat, 2 hours, 20 hours?  If it is too massive, and the release is 20 hours, then it will basically equilibrate when you are doing a lot of burn cycles, and not do much good.

Unless you entomb the stove in masonry, most of the heat will still escape, and the mass will capture a fraction only.  It should help some, but it won't be nearly as good as MH of the same mass.

If I were do it, and feeling experimental, I would be tempted to leave some voids in the masonry for channels (like a heatilator).  If the mass is cooling off too slowly without the channels, open them.  If they are cooling too fast with the channels, close them.  If not enough heat is being captured, blow some heat in there.  IOW, you'd have options.


----------



## Seasoned Oak (Sep 15, 2013)

I think the stone would heat up nicely as the sides and back of the stove would be very close to the stone. I wont do a MH at my present location as i plan to move within 2 Yrs . But perhaps some kind of hybrid system may work.Id like to work water into the mix. Heat source is full solar today. 55 outside but sunny. You may be right that the stone may not capture enough of the heat but my burn times are about 12-15 hours load. At present i use the whole house as a heat sink,stove or solar heats it to around 80 ,takes half a day to get below 70 again after stove is out or overnight. So 1 load a day with no sun. Zero loads with sun. Very cold weather & no sun = 1-2 loads in the stove.


----------



## byQ (Sep 15, 2013)

_The other issue, of course, is that MHs and superinsulated houses are not really compatible.  A right-sized MH might be the 'ultimate' wood heating appliance for traditional construction, but with the lower heat loads of a 'modern' efficient house, even in Idaho, a MH might consistently overheat the place unless you make it so small that it works more like a stove anyway._


What exactly is a masonry heater and exactly how does it work? It is a double walled thermal mass unit that is usually charged by a load of firewood. The load of firewood is burned rapidly in 1.5 to 3 hours. The heat energy from this chemical reaction is absorbed into the thermal mass. The outer surface of the thermal mass than radiates heat energy into the surroundings. If you want less radiant energy you charge the masonry mass with less energy. Which means the outside of the thermal mass will be at a lower temperature. Which means a good sized masonry heater won't overheat a superinsulated house if you charge the thermal mass with less energy - burn a smaller load of firewood. (So the outer wall of the masonry heater is say 120 F instead of 150 F).

In places where kachelofens and masonry heaters are common (Northern Europe) you will sometimes find large masonry heaters/kachelofens in small cottages. The cottage is heated by the owners burning small loads of wood like an armload of branches.

Superinsulated/supertight houses kind of remind me of being trapped underground in a coffin. And yes I've heard of an HRV. I would rather have a house that "breathes" a little bit and equates itself to the outer environment.


----------



## Seasoned Oak (Sep 15, 2013)

byQ
WHat do you mean by double wall. Is there an air space inside?  I was under the impression the masonry was solid between the interior flue area and the exterior . Also ,what would say the average weight of a small-medium  one is.


----------



## byQ (Sep 15, 2013)

_WHat do you mean by double wall. Is there an air space inside?  I was under the impression the masonry was solid between the interior flue area and the exterior . Also ,what would say the average weight of a small-medium  one is._

Yes there is a small air space or better said an expansion space between a core and an outer layer. Instead of air this space could be cardboard, mineral wool, or fiberglass material. A masonry heater has an inner part (made of firebricks, soapstone, and/or that thermal cement stuff). Once the builder has made this inner part he raps it with cardboard or fiberglass material and than builds the outer part (sometimes they build the 2 layers at the same time).

There has to be an air gap/expansion joint between the 2 layers or else you'll have crack city - that is the inner firebrick part will expand and start cracking the outer layer (the part you see) - because the heat is trapped. Too big a gap an you have poor heat transfer from the inner part to the outer part. Too small or no gap and you have great heat transfer but cracking.

I'm not an expert on masonry heater weights. But I would say a very small one could be 2000 pounds and a large one 12,000 pounds. In general a small MH is probably 3-5,000 #'s, and a medium 6000 to 8,000 pounds. Here are a couple of very small masonry heaters. The first one has firebrick on the inside (the inner core) and the builder is using 24" x 24" flue tile. He just straps the 2 halves together with metal strapping. And the second one is an experimental MH where there is only one layer - a core.


----------



## woodgeek (Sep 15, 2013)

byQ said:


> _The other issue, of course, is that MHs and superinsulated houses are not really compatible.  A right-sized MH might be the 'ultimate' wood heating appliance for traditional construction, but with the lower heat loads of a 'modern' efficient house, even in Idaho, a MH might consistently overheat the place unless you make it so small that it works more like a stove anyway._
> 
> What exactly is a masonry heater and exactly how does it work? It is a double walled thermal mass unit that is usually charged by a load of firewood. The load of firewood is burned rapidly in 1.5 to 3 hours. The heat energy from this chemical reaction is absorbed into the thermal mass. The outer surface of the thermal mass than radiates heat energy into the surroundings. If you want less radiant energy you charge the masonry mass with less energy. Which means the outside of the thermal mass will be at a lower temperature. Which means a good sized masonry heater won't overheat a superinsulated house if you charge the thermal mass with less energy - burn a smaller load of firewood. (So the outer wall of the masonry heater is say 120 F instead of 150 F).
> 
> In places where kachelofens and masonry heaters are common (Northern Europe) you will sometimes find large masonry heaters/kachelofens in small cottages. The cottage is heated by the owners burning small loads of wood like an armload of branches.



Got it.  I think the project Gary linked made sense, but was non-standard in the sense of being a retrofit situation with a large thermal mass.  I think masonry heaters are a great way to get nice even heat, with a good throttle, in cold climates and heat loads from traditional construction.  But you are not building a stone cottage in Europe 200 years ago.  You can build, if you want, a properly insulated modern house that uses a small fraction as much heat.  While you can def build a MH and burn one small load in it a day, just seems like overkill.  Like putting a cessna engine in honda civic, and driving around town at 10% throttle.  You could, but why?


----------



## Seasoned Oak (Sep 15, 2013)

THe thing about adding solar gain is, you only need intermittent heat from other sources on sunless days. Sunny days in winter would give you all the heat you need for a well insulated house. I get 65-70% of the my heat a day from solar on sunny days and my place is 100YRs old  and only partially insulated. If i ever take the insulations levels up, i would have to get a much smaller stove.


----------



## byQ (Sep 15, 2013)

_Got it.  I think the project Gary linked made sense, but was non-standard in the sense of being a retrofit situation with a large thermal mass.  I think masonry heaters are a great way to get nice even heat, with a good throttle, in cold climates and heat loads from traditional construction.  But you are not building a stone cottage in Europe 200 years ago.  You can build, if you want, a properly insulated modern house that uses a small fraction as much heat.  While you can def build a MH and burn one small load in it a day, just seems like overkill.  Like putting a cessna engine in honda civic, and driving around town at 10% throttle.  You could, but why?_

That is a good point. I never really considered superinsulation only although I am familiar with it. And I have learned some insulation tricks from it. But no I'm not putting 15" of rigid board insulation under a slab. And no complicated double wall construction. I prefer simplicity.

For me it feels safer to use the multi approach (as you mentioned).  Cost-wise superinsulation can be expensive especially anything related to spray-on type foam. My thermal mass walls - $650 and a lot of time (including discounted new windows)

There seems to be a new fad (just like that 70's thermal mass and tons of south facing windows fad) about superinsulation. Superinsulation/supertight often results in a static unchanged internal home environment that is lifeless and unconnected to the outer world. I think it is good to have the outer environment "infringing" a bit on the inner environment. I'm kind of anti-mechanical house systems (more to fail and maintain). I want things simple and uncomplicated, within reason, but efficient.

I understand that houses could be built where the amount of people living within the home (people as btu producers) and simply cooking could heat the house. But this isn't for me and seems kind of radical. The more builders go in this direction the more they will have to develop mechanical systems to "naturalize" the home environment. Old leaky houses are innefficient but still quite liveable to inhabit.


----------



## woodgeek (Sep 15, 2013)

Understood.  Many green builders (and I too) would agree that Passive house takes things too far, and is faddish and costly.  The 'pretty good house' folks are aiming for simplicity, resilience, and minimum cost of ownership.  The take away is that there is a big sweet spot between a current code house (5 BTU/sq ft/HDD) and a Passive House (1 BTU/sq ft/HDD).  The PGH people go for 2-4" under the slab (like you), and minimal cost options elsewhere.  Finish details like airsealing and thermal bridging matter (they like conventional framing and exterior foam), but the details are well understood at this point and mature tech.  Whatever your heating system looks like, anyone interested in building a low energy, resilient house should have a good knowledge of building science and best practice airsealing and insulation.

Your house is gonna rock.  Keep us informed.


----------



## semipro (Sep 16, 2013)

Interesting discussion.  A few random thoughts.
BeGreen mentions heating calculations.   The OP might want to look up "Manual J".
I've always thought a downside to MHs was a "dirty" burn and the associated need to frequently clean the units since the flue operates at low temps (or am I thinking of something else?).
MHs seem like a lot of expense/trouble when compared to a modern stove/insert and  big investment of space/money/time for something that might not work well if not implemented properly. 
In general, I like the idea of thermal mass in a house for temp maintenance.  I've found that our large stone masonry fireplace retrofitted with wood stove and our plaster walls provide quite a bit of thermal mass in our house.  I think the interesting thing about the plaster walls is that the surface to mass ratio is so high by nature. 
The balance between thermal mass and heat transfer rates is critical to system efficiency as I think others have mentioned.

Edit: The OP mentioned that he'd rather have a leaky house than a tight one.  While that may be a good thing with respect to air quality it may present lots of problems with respect to moisture control.


----------



## Seasoned Oak (Sep 16, 2013)

semipro said:


> I
> I've always thought a downside to MHs was a "dirty" burn and the associated need to frequently clean the units since the flue operates at low temps (or am I thinking of something else?).
> MHs seem like a lot of expense/trouble when compared to a modern stove/insert and  big investment of space/money/time for something that might not work well if not implemented properly.


I dont see how they get any reburn of the smoke,unless there is a superheated fresh air intake somewhere in there to feed oxygen to the smoke before it exits the stove. THe claims are that its burned wide open with no smoldering of the wood but that still leaves a lot of cold stone and low temp flue on start up to condense smoke onto. Possibly its burned off later when the whole mass heats up sufficiently.


----------



## Seasoned Oak (Sep 16, 2013)

One ? iv been pondering is :  Do any of the hearth members here have one of these stoves in operation that they care to comment on as to its performance.


----------



## byQ (Sep 16, 2013)

_Interesting discussion.  A few random thoughts.
BeGreen mentions heating calculations.   The OP might want to look up "Manual J".
I've always thought a downside to MHs was a "dirty" burn and the associated need to frequently clean the units since the flue operates at low temps (or am I thinking of something else?).
MHs seem like a lot of expense/trouble when compared to a modern stove/insert and  big investment of space/money/time for something that might not work well if not implemented properly. 
In general, I like the idea of thermal mass in a house for temp maintenance.  I've found that our large stone masonry fireplace retrofitted with wood stove and our plaster walls provide quite a bit of thermal mass in our house.  I think the interesting thing about the plaster walls is that the surface to mass ratio is so high by nature. 
The balance between thermal mass and heat transfer rates is critical to system efficiency as I think others have mentioned.

Edit: The OP mentioned that he'd rather have a leaky house than a tight one.  While that may be a good thing with respect to air quality it may present lots of problems with respect to moisture control.
_
semipro_, _
MH's burn area (firebox & area above) get hotter than any wood burning appliance. A MH  basically contains a calatytic combuster the size of a small x-mas tree. So the opposite is true - less cleaning. I see on this sight where wood burners are interested in inserts, fireplaces, OWB's, wood stoves, pellet stoves, etc.... but seldom interested in MH's. The reason for so much interest in lesser wood burning appliances? The only thing I can think of is ignorance. Yes MH's are the apex wood burning predator - they are #1. 

#1 not in terms of price, & not in terms of space taken up. But in actual firewood burning MH's are the best, the most green and efficient way to burn firewood. Older people who own them like that they don't take as much work as whatever they had before - they use less wood and they are operated only 1-3 hours a day.

On the leaky house vs tight house, woodgeek and I were talking about those superinsulated superhaus standards. These houses can be so insulated that the inhabitant's heat output can have an effect on the BTU's needed. In this kind of " haus" moisture and gases have to be dealt with because they won't leave the overbuilt house environment without mechanical assistance (an HRV). And humans breath oxygen which is depleted unless replaced. I'm for house insulation but good is good enough.


----------



## byQ (Sep 16, 2013)

Here is an example of a masonry heater in action from Australia.

The wood is burned. Most of the energy from the burn is absorbed into an inner shell (the core) above the firebox. Unlike a woodstove the heat can't get out through the walls -  it's trapped (1600 to 1800 F, trapped vs wood stove about half this). The energy starts heating the mass. It travels from the inner shell to the outer shell.

There is a small gap between the shells (the width of a piece of cardboard) or else the inner core would crack the outer shell.  The fire is done after a few hours but most of the energy is "apprehended/delayed from escaping" in the mass. It takes about 12-24 hours for the heat to escape. This heat evenly radiates outward, like the sun.

MH's aren't that complicated just the laws of physics in action.


----------



## Seasoned Oak (Sep 16, 2013)

byQ said:


> semipro_, _
> MH's burn area (firebox & area above) get hotter than any wood burning appliance. A MH  basically contains a calatytic combuster the size of a small x-mas tree. So the opposite is true - less cleaning. I see on this sight where wood burners are interested in inserts, fireplaces, OWB's, wood stoves, pellet stoves, etc.... but seldom interested in MH's. The reason for so much interest in lesser wood burning appliances? The only thing I can think of is ignorance. Yes MH's are the apex wood burning predator - they are #1.
> #.


I disagree on the reason they are not as popular.
I would say its cost,size,complexity and weight that keeps interest low. Where i can purchase an EPA wood burning stove for $500-600 ,bring it home and have it burning producing clean heat an hour later its a whole different story with a MH. Another reason i wont consider one here is i plan on moving in a year or two. Id really like to get some opinions from someone who actually owns and operates one.
Its hard to form an accurate opinion of a stove from what you read in a book or view in a video.


----------



## Seasoned Oak (Sep 17, 2013)

byQ said:


> The wood is burned. Most of the energy from the burn is absorbed into an inner shell (the core) above the firebox. Unlike a woodstove the heat can't get out through the walls -  it's trapped (1600 to 1800 F, trapped vs wood stove about half this).


You are wrong on your wood stove temps.Your comparing woodstove outside stovetop temps to the interior fire temps of MHs. Outside stovetop temps are 600-700 degrees. Inside temps of EPA woodstoves are in the neighborhood of 1600+ Deg. Smoke will not even ignite below 1100 Deg. THe only REAL difference between the two stoves is the rate at which the heat is dissipated.


----------



## semipro (Sep 17, 2013)

Seasoned Oak said:


> THe only REAL difference between the two stoves is the rate at which the heat is dissipated.


I'm starting to wonder if you're not right Randy.
When it comes down to it, overall, effective wood heating efficiency is simply how much heat enters the living area of the house per a given amount of wood.  
Inefficiencies are indicated by how much heat and unburned fuel exit the flue and how much unburned fuel remains in the accumulates in the flue and remains in the ashes. 
I suspect that burning a fire in cold firebox and flue and then let it smolder out may not be the most efficient or clean way to burn.  
In general, optimized, steady-state combustion processes as opposed to batch processes are more efficient. 

I'd love to see some "science" on masonry heaters but I've been unable to find much thus far, just a lot of anecdotal info.  

Somehow this whole discussion reminds me of the debate about the "gentle heat" produced by soapstone stoves.


----------



## Seasoned Oak (Sep 17, 2013)

semipro said:


> I'd love to see some "science" on masonry heaters but I've been unable to find much thus far, just a lot of anecdotal info.
> .


Dont get me wrong Semipro,id love to have one of these babies (MH)to experiment with. That said i know im getting about as much heat out of the wood i burn as possible in any stove. burning smoke at 1600 DEG plus with a flue pipe temp a few feet above at 250 Deg.Woodstoves compensate for quickly shedding heat with the ability to regulate the fire,slow it down while still maintaining clean burning over many hours. The mass in my system is a 3000SF house that once heated to the high 70s does not cool off for probably about as long as it takes a masonry heater to cool off. One downside i see with the MH is, it wont heat up a cold house as quickly as a wood stove. Your going to have to wait hours for the heat to work its way thru the stone.
Im just saying that a good EPA steel woodstove is not an inferior product ,just a different delivery system.IMO


----------



## Seasoned Oak (Sep 22, 2013)

Does anyone sell a kit to put together a MH sort of like they do with a log house? I not interested in building my own MH from scratch,but if i could buy a kit  or some sort of pre-fab unit i could assemble then  id be very interested. EDIT : This looks interesting.
http://masonryheat.com/2009/02/15/precast-core-up-close/


----------



## begreen (Sep 22, 2013)

Have you taken a look at Tempcast?

http://www.tempcast.com/


----------



## byQ (Sep 24, 2013)

_Sorry, I tried to get rid of the above but it posted anyway.  I have one I've decided to sell, as I don't really have a place for it.  If your interested ,Seasoned, PM me.  I'll give you first shot before I put it up in the sale forum, and C-list._

Ehouse, Could you PM me about your masonry heater. Thanks


----------



## Ehouse (Sep 25, 2013)

byQ said:


> _Sorry, I tried to get rid of the above but it posted anyway.  I have one I've decided to sell, as I don't really have a place for it.  If your interested ,Seasoned, PM me.  I'll give you first shot before I put it up in the sale forum, and C-list._
> 
> Ehoue, Could you PM me about your masonry heater. Thanks




Have done so.


----------



## Frozen Canuck (Sep 25, 2013)

Seasoned oak, semipro. 

If you would like to post your questions about the masonry heater in the boiler room we have a few members familiar with them. Sorry the names fail me now but one member was involved with Prof Dick Hill when he work on these years ago. He can likely refer you to all of the Prof's work & documents.

Hope this helps.


----------



## semipro (Sep 26, 2013)

Frozen Canuck said:


> Seasoned oak, semipro.
> 
> If you would like to post your questions about the masonry heater in the boiler room we have a few members familiar with them. Sorry the names fail me now but one member was involved with Prof Dick Hill when he work on these years ago. He can likely refer you to all of the Prof's work & documents.
> 
> Hope this helps.


Thanks Canuck.  I found some promising information based on a search for "Richard Hill" and "masonry heater". 
http://mha-net.org/docs/v8n2/v8n2-tech.htm


----------



## Seasoned Oak (Sep 26, 2013)

Im wondering if a MH can be constructed from solid cement blocks with fire brick lining. I mean 3-6K for precast sections seems a bit much. A lot of dough for a few sections of concrete.


----------



## Frozen Canuck (Sep 26, 2013)

semipro said:


> Thanks Canuck.  I found some promising information based on a search for "Richard Hill" and "masonry heater".
> http://mha-net.org/docs/v8n2/v8n2-tech.htm



Yep that's the Prof, happy reading. If the Prof is still with us he is in his 90's now. I think Tom in Maine is the member I was referring to earlier. Worth a shot in the boiler room.


----------



## Frozen Canuck (Sep 26, 2013)

Oh last we heard the Prof was living in an apartment heated by a masonry heater in his late 80's. Not sure if he built it himself at that age or supervised the build.


----------



## semipro (Sep 27, 2013)

semipro said:


> Thanks Canuck.  I found some promising information based on a search for "Richard Hill" and "masonry heater".
> http://mha-net.org/docs/v8n2/v8n2-tech.htm


What I've read so far on MHs indicates real efficiencies of between 71% and 79%.  That compares favorably with modern wood stoves. 
I'll need to read further to understand emissions and maintenance issues.  
I have to admit that the idea of building one hot fire and letting it burn out to heat the house for a day is an attractive concept.


----------



## Seasoned Oak (Sep 27, 2013)

semipro said:


> What I've read so far on MHs indicates real efficiencies of between 71% and 79%.  That compares favorably with modern wood stoves.
> I'll need to read further to understand emissions and maintenance issues.
> I have to admit that the idea of building one hot fire and letting it burn out to heat the house for a day is an attractive concept.


Same principal as a wood gassifier boiler with storage. THat system can let you use the heat for days after the fire in mild weather. Plus its a cleaner burn. MOs tlikely less costly and nat as hard to install and setup. IN the meantime i will experiment with surrounding my wood stove with a few ton of concrete blocks for heat storage to see the results.


----------



## Frozen Canuck (Sep 27, 2013)

Seasoned Oak said:


> Same principal as a wood gassifier boiler with storage. THat system can let you use the heat for days after the fire in mild weather. Plus its a cleaner burn. MOs tlikely less costly and nat as hard to install and setup.* IN the meantime i will experiment with surrounding my wood stove with a few ton of concrete blocks for heat storage to see the results.[*/quote]
> 
> 
> 
> ...


----------



## Seasoned Oak (Sep 28, 2013)

Frozen Canuck said:


> Sure hope that stove is in the basement with a good concrete floor under it. Wooden floors likely won't care for that much point loading.


It is. Even with the uninsulated concrete basement walls it still gets 95Deg in the stove room. Possibly i can capture some of that heat for later use.


----------

