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Greenhouse Heater Calculator

If you live in a cool region, you'll probably need to purchase a greenhouse heater. Heaters are rated by the amount of BTU's they produce. In order to determine the correct size of greenhouse heater needed for your greenhouse, you'll first need to gather some information on the size of your greenhouse, the minimum outside temperature you expect for your area, and the minimum temperature you want to maintain in your hobby greenhouse. Read more about heating your greenhouse.

Use the JavaScript Greenhouse Heater BTU Calculator to determine your needs:

JavaScript Greenhouse Heater BTU Calculator
Do This JavaScript Calculator Example (consider our 8' Gardener's Oasis Greenhouse)
Find the total square feet of exposed surface area of your greenhouse.

9 sheets of Solexx (at 4x8 sheet) would be 9 x 32 = 288 sq.ft.
Determine the maximum inside temperature you want to keep your greenhouse at.

You're growing seedlings, so you want the inside temperature to stay at 60º F.
Determine the minimum outside temperature you expect for your area.

You live in oregon, and you expect temperatures to be down to 20º F this winter.
Determine the heat loss factor (U-value) for the greenhouse covering material (see below).

Solexx (3.5mm) has a heat loss value of .48
Multiply the square feet by difference in temperatures, then by the heat loss factor. The total square footage of the covering surface area is 288. the temperature difference is 40º F (60º F minus 20º F). The heat loss factor is .48
This is the minimum heater BTU rating to keep your greenhouse at the desired temperature during the coldest time of year. 288 x 40 x .48 = 5529.60

Greenhouse Covering U-Values

Greenhouse Covering U-Value
5mm Solexx Panels 0.43
3.5mm Solexx Panels 0.48
8mm Triple Wall Polycarbonate 0.50
Double Pane Storm Windows 0.50
10mm Twin-Wall Polycarbonate 0.53
8mm Twin-Wall Polycarbonate 0.63
6mm Twin-Wall Polycarbonate 0.65
4mm Twin-Wall Polycarbonate 0.70
Single Pane Glass, 3mm 1.05
Poly Film, 6mm 1.20

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