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Masonry Heaters

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Gunner, Oct 11, 2006.

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  1. Gunner

    Gunner New Member

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    Does anyone have a masonry heater? I had no idea what they were until someone else mentioned them in another post. Have been surfing a couple of sites and man they are neat. Heat your house from 2 fires a day, I still find that hard to believe. Must have a hard time bringing a cold house up to temp...but they must be the cats a$$ in the spring and fall. Was reading that you must wait 5hrs between fires so as not to overheat the unit. A masonry heater and woodstove would be the ultimate.

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  2. Gunner

    Gunner New Member

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  3. Rhone

    Rhone Minister of Fire

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    The main site for them is http://mha-net.org/ and the only member I know for certain that has a masonry heater is Marty S, not to be confused with Marty.

    They used to be the cats meow, they were invented when there was a tree shortage in Europe. They were around 75%+ efficient in a time people were using fireplaces that were like 0-10% efficient. With todays stoves, they don't compete like they used to... todays stoves are like 73-75% efficient so there aren't the contrast there used to be. Masonry heaters are still mainly radiant heat which is a healthy form, and you do light fewer fires, and offer consistent outputs. They work on the principle of what's called in the industry "mean radiant temperature". That is, radiant energy over air temperature is the single most important factor for determining comfort level. It's in my energy books, and someday I'm going to scan in the pages explaining it as well, this site talks about it also. You basically take the temperature of all objects in the room based on their proportion and that determines if you're comfortable or not, more so than air temperature. That's why if the air temp is 72 and you're sitting near a masonry heater you'll feel way too hot. But, if the air temp is 60 you'll feel nice and comfy. That's also why if the air temp is 72 and you're sitting near a big 50 degree window you're going to be uncomfortably cold even though the air temp is 72 (and also why in winter you can sit in a car that's 72 degrees wearing a winter coat/sweater and be comfortable, don't try that in summer. All the glass & objects in the car are still freezing lowering the mean radiant temperature. As the objects in the car warm up (as in long trips) you'll slowly start to feel more & more uncomfortable even though the air temp is still 72). With Masonry heaters, normally you design the house so as many rooms/walls share a commonality with it or its flue.

    Anyway, I only know Marty S that has one.
  4. begreen

    begreen Mooderator Staff Member

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  5. Gunner

    Gunner New Member

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    I have now...thanks for the link.
  6. wg_bent

    wg_bent Minister of Fire

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    Intersting point. The car example was great. The one peice that I guess I don't understand here then is the effect the masonry heater has on the ambient air temp. The Masonry heater will attempt to warm all the objects in the room, just as a wood stove will, which in turn warms the room air. Probably not to the extent that a wood stove does since the difference in locally VERY hot air near a wood stove will cause dramatic convection currents. For example: If I stand in the door way of my livingroom, I'm also at the bottom of the stairs to the bedrooms. There is an unbelievably cold river of air running down the stairs and an equally serious current of hot air near the stairs ceiling. I believe that's mostly due to the fact that the very hot air coming off the wood stove and the reletively warm Living Room is setting up those currents. By your above statement this would not happen with a masonry heater since the air is not warmed much beyond pleasant room temp...did I get that right?

    So the only thing that really comes out of this is that Masonry heaters may be really awsome BUT, the house needs to be designed around them instead of added to a more typical home that is a more closed floor plan....o.k. I needed to type that out before it made sense...seems to now
  7. smirnov3

    smirnov3 Feeling the Heat

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    Ok, I don't get it.

    You say that a masonry heater has the same efficiency as a wood stove, but that you need to load it less often to maintain temperature.

    So does that mean you load more wood in at one time than into a regular stove?
  8. wg_bent

    wg_bent Minister of Fire

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    Masonry heaters are about 90% efficient, but also, yes...larger loads from what I understand.
  9. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    You load'em large and fire the crap out of them. At temps that would melt a wood stove.
  10. smirnov3

    smirnov3 Feeling the Heat

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    I was reading a little about Masonry heaters, and I just realized that they feature in many russian folk tales!

    Traditionally, Russians would put a bed on top of their heater, and that is where the parents or sick/infirm children would sleep.

    in the stories, Ivan the Idiot (the traditional hero in many russian folk tales) sleeps there.
  11. Rhone

    Rhone Minister of Fire

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    Yup, sounds right. A masonry heater does add some convection, I liked the saying "A tub full of warm water has more energy than a kettle full of boiling" but it's not much. Like you said, the temp difference isn't extreme so there's not a lot. I too easily feel it moving around my house. Extremeties that don't share a commonality with the masonry heater or its flue are particularly problematic. At the end of this I include a Q&A link about masonry heaters I enjoyed reading. Particularly read the "Heating a Long House" questions where someone wants to know how to get the heat from the masonry heater to extremeties of a long house, and the next what about using a fan to suck the cold air from the extremeties and have them return it around the masonry heater. Both responses indicate masonry heaters don't work like that since, one requires the installation of a hydronic heating system to move the heat, and the other simply doesn't work with masonry heaters. Here's the link I enjoyed reading and it does mention retrofitting as well and its complications.
  12. wg_bent

    wg_bent Minister of Fire

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    I like the question on heating a long house...

    He plans on enclosing his rooms with walls. Uhhh isn't that typically how you enclose a room?
    Never seen one with 5 ceilings!!
  13. Burn-1

    Burn-1 Feeling the Heat

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    I have, well four ceilings anyway.

    Attached Files:

  14. wg_bent

    wg_bent Minister of Fire

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    I don't need to...These guys did. O.k. so my memory was off....it was 88% efficiency for a bake oven model. 80-85% efficient with a non-bake oven model, so roughly same as the better wood stoves. I guess it comes down to a matter of life style and of course cash to throw at the solution. A masonry heater is a 20k wood stove. In the grand scheme of things, probably not very cost effective, but if you want to build a house with a real masonry fireplace, it's a no brainer.

    Masonry heater efficiency data linky
  15. smirnov3

    smirnov3 Feeling the Heat

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    EPA website claims them as being 90% efficient (maybe they are being overly idealistic, or maybe they tested a diffrent design).

    I have also seen some claims that they emit fewer particulates than most stoves (ie they are on par with pellet stoves)

    So there may be a slight advantage there, though the price tag starts at about $10k, and that's if you aren't retrofitting (higher if you are)
  16. Rhone

    Rhone Minister of Fire

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    There's combustion efficiency, transfer efficiency, and overall efficiency. Dylan was pointing out if a Masonry heater was over 80% total efficiency, so much heat would be transferred out of the exhaust there wouldn't be anything left to power draft and they wouldn't function. Because masonry heaters don't have powered exhaust, they can't be over 80% total. In previous posts, it was discussed that wood stoves over 80% total efficiency have been invented, and there wasn't enough heat escaping to power draft for them to run properly. They had to put in powered exhaust fans to assist it, but then decided that would be a flop and other issues, so decided to remove some of it's transfer efficiency to drop it below 80%, that let enough heat escape to power draft. Pellet stoves are 83%+ efficiency, they don't have enough heat escaping to power draft naturally and hence their powered exhausts.

    Usually they're talking about combustion efficiency. Here's where they did some testing and, if you notice the combustion efficiency was 97.74%, wow! No need for chimney sweeping. The transfer efficiency in that link says 73.75%, and overal efficiency is 72.1% give or take 1.5 points so there's enough wasted heat for the draft to happen naturally. That's pretty darn good. Now, I can't remember exactly what a wood stoves 73% efficiency means...
  17. Burn-1

    Burn-1 Feeling the Heat

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    When I read this I was thinking the numbers were for combustion efficiency but they're the overall numbers.

    Look at the photo below I got from the Maine Wood Heat site with a white hot afterburner jet of secondary combustion going into the bakeoven chamber. Masonry heaters don't have to worry about draft because they're burned full throttle in an excess of air until burnt out and then the damper is closed. No need for further draft concerns. There are minimal losses from combustion, (almost all chemical energy of fuel converted to heat - assuming dry fuel), like Rhonemas showed in that link, almost 98% so then most of the energy in the heater structure must radiate outward at a good heat transfer efficiency. Assume it burns at 98% combustion efficiency, it would have to have a transfer efficiency of 82% to have a overall ~80% figure. That is probably a factor of the Tulikivi being made of soapstone, and (guessing) that the Heat-Kit used in the test was made from brick. Even so the 70% overall range is good.

    Ulimately there are cost and lifestyle issues. Heaters cost beaucoup $$, need to be built around the core living areas, and are difficult to retrofit. However, they are built to last, you only need one or two quick fires per day, there are more cooking options with an oven, minimal chimney maintenance, low wood consumption, and peace of mind, (not having to worry about leaving a fire burning if you leave the house). I looked very hard into putting one into our house when we bought it but it's a 30x60 ranch with the chimney in the middle of the house and retro-fitting would have been more than I wanted to pay.

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  18. wg_bent

    wg_bent Minister of Fire

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    Dylan,

    Maybe it is sales mumbo jumbo, but the so would all wood stove claims of efficiency? MPG on cars these days?

    Given the path the smoke takes in a masonry heater vs a wood stove, it seams reasonable that a masonry heater would transfer more energy to the masonry mass than a wood stove would.

    But maybe I don't understand thermodynamics very well.
  19. smirnov3

    smirnov3 Feeling the Heat

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    Rhonemas, you seem to be the most knowlidgeable guy here about the science of heat, so do you happen to know what the transfer efficiencies are of regular wood stoves, and of pellet stoves?
  20. Rhone

    Rhone Minister of Fire

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    To understand efficiency, like a stove advertising 73% is the ratio of combustion efficiency * transfer efficiency. I've seen it repeatedly stated most modern wood stoves & inserts of today have around a 90% combustion efficiency and around 75% transfer for a total around 67% - 68%. Then, the USA uses "theoretical" efficiency whereas Europe uses "realistic". Confusing huh!? You can read about it here

    Masonry heaters are exceptional at combustion efficiency but masonry is not particularly good at transferring the heat as well as metal. On the contrary, wood stoves & inserts aren't capable of as high a combustion but metal (and soapstone) are excellent at transferring. Look at this masonry heater where it's combustion was 94.4% and transfer 65.4%. That's a total efficiency of 61.4%, less than todays stoves & inserts. That site states wood stoves have a 65% combustion efficiency, they must be using an old non-certified because your combustion efficiency must be greater than the total by a decent margin. Starting with a 65% combustion, you'd need a 105% transfer to get 68% total, impossible, draft besides. Another problem, is that your stove/insert is running most efficient at the lowest possible air setting that nets you flames and a good burn. Too much air, the heat goes up the flue before it's had time to transfer, to low and you lose combustion and hence wasted fuel out the chimney that's not transferred. I can't say exactly what the 73% is measuring or how the air was handled.

    As for pellet stoves, I don't know their combustion vs. transfer I just know many linger around 83%. This site even goes as far as saying that EPA exempt pellet stoves are not as efficient as the non-exempt ones because making a pellet stove operate at over 35:1 so they can be exempt reduces the temperature and causes less heat to be transferred. I don't know a whole lot about pellet stoves, nor their combustion or transfer percents but know the contributing factor is that the moisture in pellets is very low, and the fuel constant so the air can be precisely controlled.
  21. Roospike

    Roospike New Member

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    Rhonemas , looks like you have been doing some home work ..........I need to go refill my drink .
  22. Todd

    Todd Minister of Fire

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    Interesting read. I don't think the industry will ever come up with one sure way to test efficiency. Just too many variables. But it would be nice to see something on an even par, so you can actually compare different stoves.
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