Height of exit chimney for RMH

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:

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 .

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:

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.