Greenhouse Heater Sizing Calculator

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This JavaScript calculator will help you decide on the size of heater needed for your greenhouse, based upon your climate, desired greenhouse temperature, and the greenhouse covering.

Please note that this is an estimator only, and we offer no guarantee as to the reliability of these numbers.  We recommend that you use this calculator for preliminary sizing work, and then consult a heating professional.  Your orchid investment is worth the extra effort!

    Surface Area, in square feet, of walls, ends and roof.

    Lowest expected outdoor temperature, in °F

    Minimum desired temperature in the greenhouse, in °F

   Heat Loss Value  (1/R-value, if you know that)        

These are reasonably representative values:  
6-mil polyethylene 1.15
6-mil polyethylene double layer, inflated 0.70
Glass 1.13
"Fiberglass" or corrugated polycarbonate 1.20
Multiwall polycarbonate 4 mm 0.70
6 mm 0.65
8 mm 0.62
16 mm 0.40

    Minimum BTU Output needed from a gas heater

    Minimum Kilowatts Output needed from an electric heater

Note that these are OUTPUT values.  Most heaters are rated by their energy input requirements, with the output being the input multiplied by the efficiency factor.

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