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Greenhouse heating calculation correct?

So I plugged in some information on heating a greenhouse with natural gas in my area. My natural gas is $ 4.3070 per mcf (mcf=1000 cubic feet). The calculator I used says I'd use 6510 cu ft of natural gas per winter season. Is it naive to believe that that means I'd only use $28 worth of natural gas in an entire season? I'm not the best at math so please feel free to correct me! Just shocked at how little that actually is!


The stats I used were: 165 sq ft greenhouse made with 6 MIL polyethylene (heat lost of 1.15), heated to 40ºF for 5 months out of the year at an average low temp of 22ºF.
I'm guessing that your greenhouse measurement is off unless you have a tiny greenhouse. The calculator requires the total square footage of all exposed surfaces (walls and roof), not the floorspace.
Here in the PNW (a mild zone 8a), from December through March it costs me approximately $40 a week to heat my 11 X 16 foot greenhouse with propane. On cold nights I do supplement the heating with a small electric space heater, as needed.

Unless your greenhouse is no more than a 3 foot cube, I very much doubt your figures are accurate.

PS: what are you planning on growing that doesn't require temps over 40F? And where are you located? You've supplied zero information about your geography.
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