Hot room in Green room

[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.

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

Have you taken a look at Tempcast?

http://www.tempcast.com/

 

[byQ]

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]

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]

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]

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]

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]

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]

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]

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]

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.