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Trayc Smith wrote:
thomas rubino wrote:Hi Trayc;
Your system size looks good.
All your core measurements are within specs.
The temporary 90 to go outside is a part of the problem.
But the biggest problem I see is the exposed pipes.
They will shed their heat into the room faster than it can escape through the chimney.
I would start by placing your chimney directly through the roof.
Then I would cover those mass pipes, even if you temporarily lay rockwool over the top, that will keep the warm air moving toward your chimney.
Once you have a mass and it warms up, you should have no trouble with the draft.
Strong winds can and will have an effect at times; a special cap might be required if that is the case.
The J-Tube design is tried and proven; it will work as expected.
trayc wrote:
Thank-you so much.
The chimney is now through the roof and is working perfectly.
Next issue we are having is the cob cracking. Is it because it's drying quickly ..being fired up or maybe our mix is wrong.
Below pics of our jar test.
Test bricks seemed ok. We have used 1:4
Ratio plus straw.
Any thoughts would be great.
thomas rubino wrote:Hi Trayc;
Your system size looks good.
All your core measurements are within specs.
The temporary 90 to go outside is a part of the problem.
But the biggest problem I see is the exposed pipes.
They will shed their heat into the room faster than it can escape through the chimney.
I would start by placing your chimney directly through the roof.
Then I would cover those mass pipes, even if you temporarily lay rockwool over the top, that will keep the warm air moving toward your chimney.
Once you have a mass and it warms up, you should have no trouble with the draft.
Strong winds can and will have an effect at times; a special cap might be required if that is the case.
The J-Tube design is tried and proven; it will work as expected.
trayc wrote:
Thank-you so much.
The chimney is now through the roof and is working perfectly.
Next issue we are having is the cob cracking. Is it because it's drying quickly ..being fired up or maybe our mix is wrong.
Below pics of our jar test.
Test bricks seemed ok. We have used 1:4
Ratio plus straw.
Any thoughts would be great.
Trayc Smith wrote:
Glenn Herbert wrote:What size is your system? 6" or 8"? How many bends before it goes up in the chimney? (The last vertical bend up to the chimney doesn't count.) What are the lengths of your J-tube core elements, measured along the outer edges? What was the weather when you were testing? Warmer weather reduces the temperature differences and thus the draft.
Hi
6" system with 14" feed 231/2" burn tunnel and 48" riser. Inside measurement. CSA 5.25x5.75.
Two bends in before chimney but currently going out the wall so 90 out the wall a foot above the top of the barrel the a tee outside with rest of vertical chimney up.
We are going to change it yo a through the roof but just wanted to make sure it would work first..We also don't have a very high roof pitch (200ft off grid cabin with built-in deck extension. )
The temp for 1st test was about 10 °C. outside and still ..it seemed ok however still alot of charcoal in the feeder and burn tunnel.
2nd test was windy 8°C alot of blow back....
The feeder blocked up with hot coals due to lack of draw..didn't seem to burn as well.
Our winter temps are lows of -3 to 6°C highs of between 4-10 °C..
With frequent wind gusts .
Glenn Herbert wrote:What size is your system? 6" or 8"? How many bends before it goes up in the chimney? (The last vertical bend up to the chimney doesn't count.) What are the lengths of your J-tube core elements, measured along the outer edges? What was the weather when you were testing? Warmer weather reduces the temperature differences and thus the draft.
Trayc Smith wrote:Im looking for advice on a heat shield.
We are building the RMH in a cabin with timber framing in the walls . I've removed the drywall and cobbed between the framing for insulation. From what I've read just cob over the wood is not enough protection.
I have rocks, ceramic tiles and red brick to possibly use somehow?
Can these be used with a thick layer of cob?
Can there be gaps of cob in between the stone or tiles ?
Also has anyone tried using wool in their cob mix instead of straw?
.
Terry Byrne wrote:
Hi
We are really just wanting to protect the timber wall framing from becoming flammable. I had read this can happen over time. Code as not our focus as we don't have or want insurance.
Wood is always flammable. Continually subjecting wood to high temperatures just makes it more flammable over time.
By having a metal heat shield that is spaced away from the wood allows the flow of CONSTANT room temperature air
over the wood which creates the situation of it never being exposed to high temps, just room temps
So to emphasize - the best heat shield is metal with an air space. Just putting insulation
against a combustible material is NOT good. You get heat transfer by conduction and if it is tight
to the material there is no "chimney effect cooling" the material just keeps getting hotter.
The point of an air space with openings bottom and top will allow/create/cause a draft effect, like a
chimney, moving air which removes the heat that is being transferred to the material thru whatever material
that is being used as the heat shield.
Put another way, it is best to create the natural mechanism of hot air [chimney effect] pulling cool/cooler
air [room air temperature] over the material being heated which will perpetually cool that area.
Trayc Smith wrote:
Glenn Herbert wrote:Many styles of RMH can be made to comply with the code for masonry heaters (sometimes parts more reasonably fall under wood stove clearances), so the more things you can point to that follow code to the letter, the more likely insurance inspectors inclined to be reasonable will be able to approve an installation. Insurers not inclined to be reasonable can always find an excuse to disapprove something.
Hi
We are really just wanting to protect the timber wall framing from becoming flammable. I had read this can happen over time. Code as not our focus as we don't have or want insurance.
Our coldest temperatures range from 48F daytime down to 24F night time with a fair amount of wind over winter .
Brandon Hands wrote:I think it is important to ask: is the goal to meet US code? The minimum spacing of 1in and minimum thickness of metal is way overkill so if you're not building your rocket mass heater to code to begin with, don't worry that much about the gap or the thickness of metal.
Glenn Herbert wrote:Many styles of RMH can be made to comply with the code for masonry heaters (sometimes parts more reasonably fall under wood stove clearances), so the more things you can point to that follow code to the letter, the more likely insurance inspectors inclined to be reasonable will be able to approve an installation. Insurers not inclined to be reasonable can always find an excuse to disapprove something.