RMH blowback and too hot exhaust

Nov 28, 2014 08:27:36

Hi,
new to this forum] as a poster, but have found a lot of great info here.
we recently built a RMH for our greenhouse. the greenhouse is small and has a small aquaponics system in it.

the RMH fire does not burn sideways unless we help it - which currently means using a vac for pulling the exhaust for the entire burn. the subsequent issue is that the exhaust is very hot. so, its more like a somewhat lame wood burning stove that isn't heating our greenhouse too much.

some info:
the stove is built of non mortared bricks, the vertical portion is 8 bricks high. the cumbustion chamber is a metal trashcan. the inlet is small, a brick wide. the exhaust run is about 6 horizontal feet which goes to the outside where it T's into a 4 foot vertical run. the mass is chicken wire wrapped exhaust covered in bags of sand.

I have a lot of theories on what could be the cause, I'm just hoping that its not everything, and we can make this setup work with some modifications through the winter and consider a rebuild (*if necessary*) next summer.

any and all feedback is welcome!

Thank you!

Nov 28, 2014 09:04:27

Hello Helene,

Congrats on making the jump into the world of rocket mass heaters! I am wondering if you used any insulation around the J-tube or the heat riser. Insulation will help keep the heat riser and J-tube hot and giving a better temperature differential that results in a stronger draw. If you do rebuild I would recommend refractory firebrick, you will get much better draw using the firebrick.

It sounds like you might have a lot of air space between your sand bags on your exhaust pipe. The more material that is touching the exhaust pipe the better, it will lower the exhaust temperature.

Nov 28, 2014 09:41:51

Helene McElroy : Welcome to Permies.com / Richsoil.com, and the Rocket And the Wood Forum Threads. With 28,000+ fellow members you can come here 24/7
to talk to someone who wants to talk about what you want to talk about !

Some good news, Generally 20 ft of horizontal run thru a thermal mass is a good minimum distance. You have a potential to more than double the amount of heat you are
able to put in your G'house !

The final vertical exhaust should be on the Lee or downwind side of the G'house, this is not always possible ! On paper I can prove that a final vertical chimney that
ends just under the peak of the Roof should have a positive Venturi effect supporting the final vertical chimneys draw !

Because your winds probably do not blow gently and steadily from one direction only, The Standard 'Builders Answer' which I am recommending to you is to raise
the final vertical Chimney to a height 4' - 5' above the Peak of your roof and 10' feet away from any object bigger than a TV Antenna!

The metal trashcan will fail -and soon!

Please explain what you mean by the mass is chicken wire wrapped exhaust !

The bags of sand will be slightly insulating and slow the travel of the heat energy you are trying to harvest, we can help here too !

please Consider Strongly going to Rocketstoves.com to download a PDF Copy of the brand new 3rd edition of Rocket Mss Heaters This will put the information in
your hand immediately and from there you will find where your Design wanders too far from other models (100,000 + ) that have worked, AND it will help
you when you talk with Your other Fellow Members here at Permies .Com .

Add enough vertical stovepipe to rise over the peak of your roof and get the Book ! Both of these will help you a great deal !

For the good of the craft ! big AL

Nov 28, 2014 09:56:43

Well, to troubleshoot, we need:

1 drawing of the thing, vaguely to scale and with the materials used.

2 pics!

3 a proper description with dimensions. If possible using the right terminology.

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