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Captured heat and greenhouses

 
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I am in the early stages of building a 8x8 green house as a extension  of my wood boiler shed.  The green house will be built out of reclaimed insulated glazing from a commercial office building.   The current shed houses  my boiler which is a 300,000 btu outdoor wood boiler that supplies heat and hot water to the main house.  The idea of the green house  was to get a early start on seedling in the spring but  i have started to wonder if i could heat it using capture heat from the wood boiler.   I have seen several homesteaders wrap the chimney flue with copper pipe to create hot water and store it in  reclaimed h/w tanks.  What i am wondering is if i wrap the flue and store any hot water created  in a 55 gallon drum ( or 2)  in the center of my 8x8 greenhouse would it radiate enough heat to keep the green house warm enough to grow year round?    Any idea how much heat i could generate this way? Or what water temp i could achive? I am zone 6b by the way....
 
gardener
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I got no knowledge, but plenty if speculation.
I want just such a set up for myself, so I've been reading and noodling about it first a while.
I would insulate what ever earth you want to grow in from the surrounding soil.
I would bring the captured heat down to the root zone.
You could probably run copper up to a few feet into the ground and then be able to switch to pex or polypipe.
I'm not sure how hot the chimney, but whatever heat you extract,I'm sure you will take care to leave enough for good draw.
The greenhouse could be a great place to store fuel for your boiler.
 
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I second the suggestion to insulate the ground from the exterior.  Otherwise the outermost two feet of the greenhouse soil will be at or close to freezing all winter.  

Wrapping copper pipe around a hot pipe and running water through it is a bit tricky.  If you have a pump running all the time it should work just fine.  But if you're relying on a thermosiphon or gravity, the water can slow down enough to boil and then you have steam and other problems.

Might the boiler give off enough ambient heat to the greenhouse without any trickiness?  Or does it have an extra outlet that you could tie another heating loop to for the greenhouse?
 
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No need to reinvent the wheel. I've been in these climate battery greenhouses at 7200' in the Rockies and there were bananas and papayas and more growing in one and a 30' fig tree growing in another.

 
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