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Rocket Water Heater - Greenhouse Fish Tank

Jonathan Hall

Joined: Apr 13, 2012
Posts: 1
So I am putting together a rocket stove for my greenhouse and have dreamed up an idea and can't really seem to find any good answers out there. So hopefully someone has either done this or has some ideas why it would or would not work.

Here is the primary concept without the added modification just so you know what I am working with;

Rocket Stove, built inground (no above ground thermal mass save for the heat riser and barrel). The exhaust runs underground just below the surface and winds underneath my four IBC fish tanks. This essentially radiates up to heat the tanks as well as heating the ground as my "mass".

Now for the modification idea;

Place a stainless steel barrel (smaller) on top of the rocket stoves barrel. Place a stainless steel drain hose which will drain back into the fish tank. (Copper(brass/bronze) will not work due to toxicity issues. So stainless steel is about the only choice. Pex is a consideration but it can't take much more than 200 degrees F.

Take a very small water pump and pump the water out and into the top of the stainless water heating barrel, and then the water should essentially get heated and drain back into the fish tanks.

I considered pex tubing as it would be more movable so I could take it down easier, but it has a max temperature of 200 degrees F. I would be afraid I might melt it, so I would have to put some sort of insulation between it and the top of the rocket stove otherwise it might get too hot. This could be another alternative if steel piping is to tricky.

Alternate Option;

Make the water heater, heat exchanger a closed loop. and just have the hoses lay in the water with no waterflow to the water, just let the water cycle naturally and radiate the heat.

What do you all think?
Yone' Ward

Joined: Feb 14, 2012
Posts: 135
Location: Springdale, WA USA - Cold Mediterranean Climate
The close loop option won't get plugged and gummed up by fish debris.

Just call me Uncle Rice.
17 years in a straw bale house.
R Scott

Joined: Apr 13, 2012
Posts: 3051
Location: Kansas Zone 6a
Flexible gas line (propane/natural gas) is stainless steel. Wrap as many coils of the gas line as you can fit or afford, then cover with cob. You can change to pex at some point after, as you do not want your water over 200 and flashing to steam anyway.
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi. "Family farms work when the whole family works the farm." -- Adam Klaus
subject: Rocket Water Heater - Greenhouse Fish Tank