Another steel stove adding mass mod

Hi all !

I going on permies forum to read many interesting articles , mostly about stove and rocketstove but other subject sound interesting too !
After few year , I just decided to create a account I try to participate to that beautiful community.

Last year and this year I try many setup to adding a bit of mass for my steel wood stove with concrete cinder blocks.
I try the classical setup by making walls around it:


But another setup I try is by stacking over the stove with spacer ( 3/4 inch ) to let's the air enter under the blocks and rise inside the holes of the cinder blocks:





I get a good draft like you can see with the flame of my bick lighter:



What did you think about the two setup ? Not sure which one is better.
I think the one over the stove get warmer when I did a fire with the same amount of wood.

I'm not sure I understand what you're trying to accomplish.  You want to even out the peak-and-valley temperature swings from an old inefficient box wood stove?  Are you heating your whole house, or just the stove room?

The thermal mass of your house (walls, floors, furniture) far exceeds that of a few cinder blocks.  I'm sure the cinder blocks will stay warm for a few hours after the fire goes out, but you'd have to be standing very close to benefit.

My advice is to replace that old stove with a modern efficient one.  I burn mine 24/7 with no temperature rollercoaster effect.  The air intake is controlled by a thermostat that keeps the room temperature within +/- 2 degrees F all day and night.  I typically load the stove twice a day from November until March.

I did not quite understand the mission either.

Mass can even out the temperature extremes, but a stove can "never be hotter" because of the law of thermal dynamics. And that is, "Energy cannot be created nor destroyed." With heat, a stove burning x amount of wood...is going to produce x amount of btu's. All the mass does is absorb some of those btu's and then its warmth is felt as the room around it cools. In this way, mass is not gaining or losing btu's, it is just delaying the transfer.

This is even true with wood. Every wood type has the same amount of btu's. A ton of White Pine has the same amount of btu's as a ton of Beech. The difference is in the measure. A CORD of White Pine has a whole lot less btu's then a CORD of Beech because the wood is less dense. Since we have defined the wood as being a certain size, that size has less density for White Pine than Beech. To put it another way, 128 cubic feet of beech is going to have a lot more density to it then 128 cubic feet of White Pine.

I am not sure how much cinder blocks will help. I had an old pot bellied stove, and so I surrounded it with quite a bit of rock. I put this in a semi-circle around the stove, and it really did help my home better. As the fire died down, and morning arrived, with the rock, the room was noticeably warmer than before I added the rock. That is because at first, the rock absorbed the radiant heat from the stove, but eventually absorbed all it could because the stove was really overheating the house. As that stopped towards morning, the air in the room cooled to the point where the rocks had to give up all that extra heat to try and heat the room. So it does work.

BUT...it took a lot of rock. I am guessing it was probably at least a ton or two of rock. That would be a lot of cinder blocks.

Hi Jean;  Welcome to Permies!
Trying to improve your old box stove is better than doing nothing at all.
Personally I suggest building a RMH but...  If you can't build a rmh or don't want/can't purchase a new high efficient stove.
Then adding mass to what you have is worth it.

Go with version A)   Walls on sides and back.
Place blocks with open side down.  Fill each hole with sand before stacking the next row.
Now you have some mass to heat up and stay warm.

I still recommend building, A rocket mass heater...  check our forum out here at Permies!  We would love to help guide you thru a build!

I plan to surround my small wood stove (a Vermont Castings Aspen) with bricks on three sides and underneath.  The bricks will hold the heat some overnight, but the biggest benefit will be having an extra heat shield.  I do want to build a rocket mass heater, but that will entail cutting a big hole in the floor, reinforcing the floor joists, and pouring a footing in the middle of the house.  It’s on my list, but near the bottom right now.

Kathleen Sanderson wrote:I plan to surround my small wood stove (a Vermont Castings Aspen) with bricks on three sides and underneath.  The bricks will hold the heat some overnight, but the biggest benefit will be having an extra heat shield.  I do want to build a rocket mass heater, but that will entail cutting a big hole in the floor, reinforcing the floor joists, and pouring a footing in the middle of the house.  It’s on my list, but near the bottom right now.

Is the stove installed too close to the walls?  Or sitting on a combustible surface? ( I hope not!)

Here's the installation manual for your stove:
https://downloads.hearthnhome.com/installManuals/30000369%20Aspen_27.pdf

don't rely on loose-stacked bricks to correct a faulty installation

I do not think it is, you can see black tile in the background, and some drywall.

According to code, you can use a variety of heatshields to allow closer clearances since "the distance to combustionable walls" is therefor reduced.

Travis Johnson wrote:but a stove can "never be hotter" because of the law of thermal dynamics. And that is, "Energy cannot be created nor destroyed." With heat, a stove burning x amount of wood...is going to produce x amount of btu's. All the mass does is absorb some of those btu's and then its warmth is felt as the room around it cools. In this way, mass is not gaining or losing btu's, it is just delaying the transfer.

If the blocks were heating up they could potentially be providing pre-heated air for the stove which could make it burn hotter.  the room isn't a closed system.

Davis Tyler wrote:

Kathleen Sanderson wrote:I plan to surround my small wood stove (a Vermont Castings Aspen) with bricks on three sides and underneath.  The bricks will hold the heat some overnight, but the biggest benefit will be having an extra heat shield.  I do want to build a rocket mass heater, but that will entail cutting a big hole in the floor, reinforcing the floor joists, and pouring a footing in the middle of the house.  It’s on my list, but near the bottom right now.

Is the stove installed too close to the walls?  Or sitting on a combustible surface? ( I hope not!)

Here's the installation manual for your stove:
https://downloads.hearthnhome.com/installManuals/30000369%20Aspen_27.pdf

don't rely on loose-stacked bricks to correct a faulty installation

My stove isn’t installed at all yet.  It has been riding around in the back of my pickup (which has a cap on it) for two years, waiting for us to get moved and now for the chimney to be inspected, and fixed if necessary (there hasn’t been a wood stove in this house for at least thirty years).  At the very least, it’s probably full of mud-dauber nests!  The stove will be installed correctly.  I just like having that little extra margin that the brick will give, or stone if we had good stone for the purpose.

I do have a copy of the installation manual, but thanks for the link.

Graham Chiu wrote:

Travis Johnson wrote:but a stove can "never be hotter" because of the law of thermal dynamics. And that is, "Energy cannot be created nor destroyed." With heat, a stove burning x amount of wood...is going to produce x amount of btu's. All the mass does is absorb some of those btu's and then its warmth is felt as the room around it cools. In this way, mass is not gaining or losing btu's, it is just delaying the transfer.

If the blocks were heating up they could potentially be providing pre-heated air for the stove which could make it burn hotter.  the room isn't a closed system.

That is true I suppose. I know all the commercial boilers I used to weld up had preheated air...

Wow ! Thanks for all the interest about my topic. I never thinking about getting all this answers. More active community that I expected. Thanks again !

I know I can't create more energy from my wood coord than what it's can deliver. What happens is like many steel stove , it's deliver a lot of heat really quickly and my dreams is to keep the stove burning in the evening , stop feeding it when I go bed , and get a kind of " damping effect " that absorb all that energy as possible and deliver it slowly during the night and the next day morning. For now the stove just pour all the heat in my house really fast , getting the house too hot quickly.

I know restraint air in the stove is not the best for efficiency by getting the combustion low in oxygen , creating incomplete combustion. right ? So fast combustion with all oxygen need but with a mass to deliver it slowly sound more efficient.

Another things is a hope the draft in the second setup remove more heat from the pipe before they get lost in the chimney.

All my thinking make sense ?

EDIT: Oh and yes I want to built a rocket mass heater or a double bell mass stove someday by myself. Need to talk to my house insurance for that. This forum is a good source of informations for that. My neighbour is a masonry builder , probably I can get some advice from him too. He already coach a guy for a rocket mass heater if I remember. I need to pill up a bit of money for that project.

I currently only have 17 cinder block. Not the big one , size is 8inch x 16inc x 6inch.
It's weight 13Kg each ( 28.5lbs ).

So I have about 0.25tons of concrete. More than what I expected.
If I fill holes with concrete ( denser than sand : 2600kg/m3 vs 1600kg/m3 ), I can get extra weight and go up to 0.55tons total.

I check for this kind of mod too , because my pipe get really hot all it's length ( so a lot of heat go outside ):