Justifying Thermal Mass Effeciency Rate (pot bellied stove)

Does anyone know of a real world way to evaluate the effects of a thermal mass wall recently installed in my home?

I am not lazy, so I did an internet search but the topic seems to be more scientific then practical. I mean I know water is 4 times as efficient as the rock I used, BUT I do have a wife and do take pride in my home, and a rock wall seemed to be a practical AND aesthetically pleasing at the same time.

My intent was to improve my pot bellied stoves heating properties, and to get rid of one ugly piece of tin that was required to protect my walls from intense radiant heat. I live in Maine and have plenty of rocks, so I built this yesterday hoping to improve the looks of my stove, and to gain a little heating advantage since my house is tight enough to allow firing it once per day on the dawn and eve of the heating season (Fall and Spring).

Some of the rocks get intensely hot, while others do not seem to absorb as much which I understand is going to happen, but as a whole what is the best way to figure out if this rock wall behind my stove was worth doing? The rocks were free, as was even the diesel fuel for my tractor (long story) so I do not have a dime invested in it, but it took me 4 hours to find, haul and stack the rocks. The wife is OKAY with the looks of it...if it works. Now I need a way to justify if it stays or goes.

Any idea on how to do that?

Statistics are as follows:

Dry stacked rocks with no mortar between them
1.8 cubic yards
Slate and Granite construction mostly
4 Hour construction time
No passive solar heat: built on Northeast Wall

Here is the link to a Flickr Photo of it. (Note: My floor is currently bare concrete because we live on a thermal mass slab and are in the middle of a kitchen remodel and have yet to install the tile floor due to construction of the new kitchen).


Thermal Mass by tsj5874, on Flickr

Can't help with the thermal mass question because I am being lazy and don't want to look it up , but if votes count for anything with the wall staying or going, I vote it stays

Looks great in my opinion and something you would see in a nice log home.

OK. How to justify it??????? Momma's happy, looks good, rock will absorb, hold & radiate heat over time. Hmmmm, did I miss anything, or possibly I'm being to simplistic? Quit over thinking every thing my young friend. It is what it is. This is not the law of physics, it's the law of common sense. By the way, I'm with Momma on this, it looks good!

I certainly can't help with a mathematical formula, [I'm allergic to math ]

But the 'ugly' sheet of metal probably did a better job of reflecting heat into the room, so for reflected radiant heat,
you might not be as 'efficient' now.

But, from the stand point of absorbing and holding heat for when the stove cools down, the thermal mass of the rocks
definitely is much more efficient.

If you left the piece of metal in place, with an air gap between it and the wall, THEN stacked the rocks, this would be
ideal, the metal will still reflect some heat back against the rock wall, and keep the back wall cooler, Right now, the rocks conducting heat into the wall. Tthe steel could be hidden behind the rocks..

There is no question that the wall looks VERY nice, so even if it might be a bit less efficient, it is worth it, for the
improved appearance.

Greg L

This is not your fault I know, but if you look at the photo, on the far right side you will see a ugly brown box. This is the coal chest you speak of. It is there! What coal burning Guru worth his weight in lignite would not have that!

As for over-thinking things...oh my, yes I do that very well!!

ONEDOLLAR wrote:Nosmoke

Your rock wall looks great!! If you are happy with it and the wife is happy then keep it. Don't worry about needing a way to justify it. Your justification is in the smile on your face when you look at it.

The wall is going to absorb heat. No question about it and that is generally a good thing I would think. The only thing missing from your setup is a little chest full of coal next to the stove!

I agree with Greg,but the heat being absorbed into the stone will be most likely only benificial to that room only and not the whole house and what heat is absorbed will probally be lost do to the window above the stone. Nice job on the stone

The thermal mass is good only if you burn the stove a few hours and let it die. Then the heat absorbed by the stone wall will radiate the heat back in the room for a certain time according to the weight and material specs....
But if you burn 24/24 there is not a real big advantage for it. Once the wall is satured from heat it can't take more heat and then just send it back in the room.
That said, the look is a different question and I must agree with others, it's very nice and if everybody like it just keep it. Much nicer than a plain sheet metal.

It would be great to figure out a practical way to figure out its efficiency, but I tonight we noticed a big difference.

It was cold and windy outside, but the house was only mildly chilly at 70 degrees when we got home at 19:30 tonight. I had fired up the stove this morning about 03:30 and let it go out at 08:00, so it sat for 11-1/2 hours with no fire in its belly. I think the rocks had a big part in that, but as others said, it only helped heat my kitchen...the room the stove and rock wall is in. The farther parts of the house were 66 degrees, 4 degrees cooler, but they are bedrooms so a little cooler is not bad.

No matter what, I cannot complain; there are people who heat with gas, electricity and oil who cannot afford to keep their home maintained at this temp, so to do so at zero dollars for 19-1/2 hours is pretty good. (It is warm enough in here so that I will not get a fire going again until tomorrow morning at 03:30.)

What you have is a thermal mass storage wall. They are usually used to even out the heat in the house if you have a sporadic heat source. They do not increase efficiency. They heat up when the heat source is hot, then when it goes cold, they give back the stored heat. The measure of if it is working is to measure the temperature of the space it's in over time and compare it to when the wall wasn't there. If the space has a more constant temperature, then you have succeeded. As someone here already said, if you run the stove 24/7 it will make no difference. Heat sinks are used, for example, in passive solar houses where the sunlight is captured during daylight hours and the thermal mass storage emits heat to keep the space warm after the sun goes down..

dj