# Bricks on top of stove to increase thermal mass?



## Esprit (Feb 13, 2015)

Maybe this is a dumb question. What if one was to put bricks on the top of their woodstove? Would that increase thermal mass and help the stove radiate heat longer between load times?

Thanks
  Todd


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## mark cline (Feb 13, 2015)

A fan would be more effective.


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## HotCoals (Feb 14, 2015)

mark cline said:


> A fan would be more effective.


x2

You want heat transfer from in the box to the room.
Let the house be the heat sink.


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## bholler (Feb 14, 2015)

mark cline said:


> A fan would be more effective.


that would not help them accomplish what they are trying to do at all if anything it would slightly shorten the heat output time.  Bricks on top can help a little but not sure how much you can always try it and see what it does for you


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## nikolays (Feb 14, 2015)

OP did not ask about transfering heat instead the question was how to store some of the heat and reclame it later. My opinion you will need alot of brick to be able to see any difference better if you get peace of soapstone placed on top it would looks better too.


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## DougA (Feb 14, 2015)

If you can find someone near you that cuts soapstone kitchen countertops, ask if they will sell the sink cutout from one.  It should be very cheap and will look much nicer.  Soapstone will hold a lot more heat than a brick lb for lb.


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## FionaD (Feb 14, 2015)

Funnily enough I was wondering today about the possibility of putting a slab of soapstone on my stove top in order to store some heat overnight. My stove is too small to hold heat that makes a difference for more than five hours after a full load, but I notice that the stone wall behind the stove holds ALOT of warmth overnight that the room benefits from in the morning - it's warm then, even when the stove is cold... So was wondering about ways to add more stone = more heat store.

No problem having a full slab on top, I have a rear flue exit (Esprit, i guess you do too?) So what sort of thickness of soapstone slab would be best?


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## Grisu (Feb 14, 2015)

DougA said:


> Soapstone will hold a lot more heat than a brick lb for lb.



The heat capacity of brick and soapstone are actually very similar (0.9 to 1 J/gK). Soapstone is more dense so at the same volume it holds more heat. Nevertheless, gypsum is even slightly better at 1.1 J/gK so your drywall actually retains quite a bit of heat. I would rather look for ways to keep the heat in the house by weathersealing and insulation. That will be a better investment and make a larger difference in heat retention than piling rocks on the stove. Don't forget that those also act as an insulator for the stove top so you may lose more heat up the flue.


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## firefighterjake (Feb 14, 2015)

I put a slab of soapstone on top of my stove with a small air gap ... I haven't noticed any significant improvement ... but it does look nice.


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## branchburner (Feb 14, 2015)

I prefer a few large pots of water... adds thermal mass AND a little humidity.

Consider that you can add thermal mass to your living space by having some mass near the stove, not just on it. Obviously a brick or stone fireplace or wall holds a lot of heat, but anything else in the room (large potted plants, stone coffee table or sculpture, etc.) will absorb some heat and re-radiate it.


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## FionaD (Feb 15, 2015)

Grisu said:


> .Don't forget that those also act as an insulator for the stove top so you may lose more heat up the flue.


I'd wondered about that part....

I think Ill just stay content with the amazing storage heater I have in that sandstone wall behind my stove. An added bonus that never even occurred to me when the stove first went in.


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## BobUrban (Feb 15, 2015)

Like the pots of water on stove tops - if not mostly for looks it is mostly a waste of time.  Not in a bad way - just not valued per gained BTU in the house way.  Just like the increase in relative humidity in your home cannot be measured in a way that justifies the pot on the stove.  It is cosmetic  and we all like our stove enough to dress them up from time to time. 

Most stoves of any quality are designed to perform there best so all that heat the bricks would be absorbing would be in the room anyway.  Yes, they will likely hold onto it as stove goes into the back end of a burn cycle and slowly release it into the home but by no means at a measurable rate that you could physically notice. 

I even went so far as to think of a radiator system that I would create in the welding/blacksmith shop.  Something fancy with fins and such that would truly move heat from the stove to the room but.... upon further review, help from many here and some conversations with stove manufacturers, it became obvious that I would be robbing Peter to pay Paul so to speak. ie. stealing heat that is needed inside the stove that allows it to work properly.  This in turn would rob secondary burn and cool flue gas potentially to the point of creo and diminished return. 

I still love the idea of removable radiator plates on a stove but realize its futility.


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## begreen (Feb 15, 2015)

Maybe not? This is essentially what PE, Jotul and others have done by hanging massive plates of cast iron off the sides of the stove and in the case of the Alderlea, on top of the stove too. It does work to temper the radiant quality of the stove and slowly release it without negatively affecting the burn. The key is probably the air gap between the stove body and the plates.


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## HotCoals (Feb 15, 2015)

Grisu said:


> The heat capacity of brick and soapstone are actually very similar (0.9 to 1 J/gK). Soapstone is more dense so at the same volume it holds more heat. Nevertheless, gypsum is even slightly better at 1.1 J/gK so your drywall actually retains quite a bit of heat.* I would rather look for ways to keep the heat in the house by weathersealing and insulation. That will be a better investment and make a larger difference in heat retention than piling rocks on the stove. Don't forget that those also act as an insulator for the stove top so you may lose more heat up the flue.*




Someone who gets it. Cheers!


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## bholler (Feb 15, 2015)

I totally agree that working on the house envelope will give you allot more benefit but adding some thermal mass to the stove wont hurt anything as long as you do what bg said and leave a little air gap that stone or brick will suck up some heat in the beginning but it will in no way whatsoever send more heat up the stack that is not how it works.  It will absorb heat in the beginning and then release it later as the stove cools.  I doubt you will see much difference in heat output though I just don't think you will get enough mass to help much.


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## begreen (Feb 15, 2015)

Exactly right. No more heat, just better heat retention and later release. I think that was the point of the OP's question.


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## Ashful (Feb 15, 2015)

Grisu said:


> The heat capacity of brick and soapstone are actually very similar (0.9 to 1 J/gK). Soapstone is more dense so at the same volume it holds more heat. Nevertheless, gypsum is even slightly better at 1.1 J/gK so your drywall actually retains quite a bit of heat. I would rather look for ways to keep the heat in the house by weathersealing and insulation. That will be a better investment and make a larger difference in heat retention than piling rocks on the stove. Don't forget that those also act as an insulator for the stove top so you may lose more heat up the flue.


True, but then compare the heat capacity of a few bricks or a coupl'a pounds of soapstone to the net mass of every object within the insulated envelope of your house.  To the op:  the mass and heat capacity of the stove is not a substantial factor in extending the time a given load of wood will heat your home.  BTU in = BTU out, divided by efficiency, after all.

The reason you want mass in the stove is to help even out relatively short (eg. < 30 minute) spikes and dips in firebox temperature.


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## begreen (Feb 15, 2015)

FWIW, I think the heat capacity of soapstone is about 14% higher than common brick.


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## KindredSpiritzz (Feb 15, 2015)

For years i had 4 or 5 of those 3 inch cement blocks on my old wood stove. It never helped from what i could tell. By the time the stove cooled the cement blocks were cool as well.


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