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Old school thermal mass

Post in 'DIY and General non-hearth advice' started by EatenByLimestone, Oct 11, 2008.

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  1. EatenByLimestone

    EatenByLimestone Minister of Fire

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    I've seen some old houses with interior brick walls for picking up heat from a fireplace. I've heard of other walls with "river rocks carefully placed in the walls."

    So, building on this, would there be any advantage to put raidant heat into a concrete interior wall? Once it heats up it would probably give out heat for a good amount of time. It would also be easier to insulate from the cold ground than a slab.

    Any ideas?

    Supporting the weight would be the only downside I can think of. BTW this was the problem with the brick wall mentioned above.

    Matt

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  2. dave11

    dave11 Minister of Fire

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    I designed a radiant heat system for my own house, so I have a decent idea of the principles and theory, but i'm a little fuzzy about what you're asking. Do you mean to build a new concrete wall with a built-in radiant source? Or do you mean to retrofit an existing wall?
  3. EatenByLimestone

    EatenByLimestone Minister of Fire

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    Sorry for it being unclear. I was just thinking about how older houses used thermal mass to their advantage and how many of our more modern houses were built without any.

    I was thinking more about new construction since you could plan to support the additional weight. When putting up the interior walls, I thought of filling the spaces between the studs with concrete. This could trap heat from a woodstove or other heating device. You could even run a heating system, water or electric, up through the concrete. Concrete has the advantage of not being too expensive also.

    Would incorporating this into a structure make sense? Could this make the house into a crock pot of sorts? Low energy usage and uniform heating since all interior walls could take part? Since an interior wall has 2 sides and access to two rooms, would this save money in materials to heat a home? Could a concrete wall have an added safety measure to it in areas prone to hurricane or tornado damage?

    Could this be an efficient use of solar hot water heating? If you store the heat generated durning the day into the concrete walls of the house..

    Just a brainstorm... I have to keep my mind busy or I get myself into trouble.


    Matt
  4. dave11

    dave11 Minister of Fire

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    I see now. You have the right idea, in heating a high mass surface, but the modern convention has been, where possible, to do it with the floor. The ideal system involves a high-mass floor, made of something like gypcrete, containing a radiant heat source that trickles in just enough heat to make the floor and room comfortable. Now if you want to do that with a wood fireplace, a wall makes more sense, and I believe it was fashionable at one time to do that with a large brick fireplace surround and chimney (called Russian fireplaces?). Or another variation, a wood boiler that circulates warm water to radiators throughout the house. Same idea.

    Don't forget though that you would have to heat these surfaces up, before they could "coast." It would make for more even heating, and hence more comfort, though how much efficiency you'd gain is a function of how efficient a heat source you use, and also how well-insulated the house is.

    I live in an older home, with thick walls and floor, and for sure my house is much slower to change temperature, for the same reason you mention. Whether or not to purposely build a house this way anymore though would be a pretty intricate analysis, and would have to be done obviously pre-construction.

    So adding a heavy wall near your heat source should lead to more even heating, but not necessarily more efficiency. The house would lose heat at the same rate, wall or not.
  5. Highbeam

    Highbeam Minister of Fire

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    The concrete is a poor insulator. So to make the crockpot theory pan out you would need to insulate the exterior walls. Research ICF homes.
  6. EatenByLimestone

    EatenByLimestone Minister of Fire

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    I don't think you would want the concrete to insulate or stop/slowdown the transfer of heat. The purpose of the concrete is to absorb and then release the heat.

    Matt
  7. Dune

    Dune Minister of Fire

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    It is definitely a good idea. thermal mass is thermal mass, regardless of what form it takes. Additionaly, the comments that it may not add to efficiency are not nessasarily acurate either. When heat is absorbed by thermal mass, the rate of heat loss is slowed. Additonaly, radiate heat in any form is still radiant heat, meaning that the higher comfort level could result in a lower house temp that feels just as warm. Cat says I need to get out more so here I am. Never the less I would invest in proper insulation before adding thermal mass.
  8. 8nrider

    8nrider New Member

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    i live in a 1800 center chimney cape. we started having fires in the large (rumford)fireplace awhile ago. the wood stove was lite 2 weeks ago in flue #2. by the end of october the heat radiating from the stone and brick mass as my daughter anna says is off the chain. this thermal mass kept the residence of the home warm many many decades ago. well before fossil fuel.
  9. 8nrider

    8nrider New Member

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    moral of my story: keep the fires burning.
  10. dave11

    dave11 Minister of Fire

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    Sorry Dunebilly, but my comment on efficiency is correct. How fast the house loses heat is solely a function of the insulating values of the exterior surfaces, and the temp difference between the interior and exterior. Adding thermal mass will slow both the temp rise caused by the fireplace, and the temp fall after the fire is out, but it won't change how much heat is produced by the fireplace. In other words, the wood won't burn any hotter.

    If you want more efficiency, you need to burn hotter, or add insulation. That said, you might still gain a tiny amount of efficiency from greater thermal mass due to it's absorption of some of the peak heat, resulting in a lower peak temp per burn, and thus slightly less heat transfer outside. But if you did the calculation, you'd find it was a miniscule gain in efficiency, and surely not worth altering the house for.
  11. Dune

    Dune Minister of Fire

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    You ignored the entire second half of my post. Greater efficiency is gained by greater comfort level.
  12. dave11

    dave11 Minister of Fire

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    Except efficiency and comfort are different things. Greater comfort levels are nice, but they won't save any money. Greater efficiency saves money. So adding five hundred pounds of mass around a fireplace might make the area more comfortable, but it's not going to save any significant amount of money.
  13. Dune

    Dune Minister of Fire

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    Too sick to argue, When I am well, will revisit.
  14. Dune

    Dune Minister of Fire

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  15. EatenByLimestone

    EatenByLimestone Minister of Fire

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    What about for the guys upstairs with the Tarms, etc? Many are preoccupied with large tubs of liquid thermal mass.



    Matt
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