Green - heater Red - pvc pipe (perforated) Yellow - vent
So the idea, is to grow 12 months (zone 7b). I know it will be a yearly trial and error, but I'm getting ready to build my lean to on my garage. In order to grow extra months, you need heat, yes? So I am figuring, instead of just hanging a heater, why not try to utilize that heat more efficiently. Per the drawing, I would blow the heat into the heat sink (gravel). Figuring that the heat then, will be more efficient and give off a radiant heat to reduce the amount of time the heater is on.
With time and money anything is doable. So I vote that you do what you want and have fun doing it.
That said, I have to ask why do you want to store the heat vs just create it as it is needed with electricity.
With day time solar, we are forced to store it.
With summer time solar we are forced to store it for the winter.
Even with a wood stove we are forced to store the heat (RMH) because we don't want to wake up every 3hrs to add wood.
Plants are more worried about their roots/soil temperature changing temperature 5F and less about their leaves/air having a 30F daily temperature swing.
Also are you making your electricity onsite from solar panels?
Is this electric heat, waste heat from some other operation that you are doing?
I would rather heat with natural gas and get all 100% of the heat onsite vs, have the power company burn natural gas (or worse coal) and throw away 67% of the heat, only sending 33% as electricity.
Also the CO2 enrichment in the greenhouse is super good for the plants, they love CO2.
Iterations are fine, we don't have to be perfect
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