It's Just a Gardening for Fun Blog: Gardening Tools and Calculators

Free Greenhouse and Gardening Calculation Tools: Share this With You're Friends!

Calculators:

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Explanation: This calculator is designed to calculate and give an estimate of the BTU (British Thermal Unit) greenhouses heat requirements. Simply enter the area to be heated and select the climate adjustments. This is to be used for a general guideline only.

	Greenhouse Area The total square feet of exposed surface area of your greenhouse not including the floor (This is not length * width). To find out the area your greenhouse, click here.
	Coldest Outside Temperature You will want to enter the lowest temperature expected for your area. Not sure? You can click here for the USDA plant hardiness zones which provide an average annual temperature rating for areas within the United States.
	Maximum Inside Temperature This is the highest temperature you want to maintain in your greenhouse.
	Heat Loss Value Check the table at the bottom of the page to find the heat loss value for the covering used on your greenhouse. Some values may vary with manufacturer. If you know the R-value of your covering, you can convert it to a heat loss value using this formula: Heat loss value = 1 / R-value.

Resulting Minimum BTU

This is the minimum BTU output your heater should have. Most heaters use a BTU input rating.
BTU Output = (Heater Efficiency) * (BTU input).

This result is: Area x (Max - Min) x Heat Loss

Covering Insulation (R) Values for Polycarbonate, Polyethylene, Glass, and Fiberglass
Covering Material	R Value	Covering Material	R Value
3 mm Glass (single layer)	0.95	4 mm Twin-wall Poly	1.43
Two layers of Glass (insulated)	2.00	6 mm Twin-wall Poly	1.54
8 mm Twin-wall Poly	1.61	4 mm Polyethylene	0.83
10mm Twin-wall Poly	1.89	6 mm Poly	0.87
16 mm Triple-wall Poly	2.50	6 mm Poly double layer (inflated)	1.43
Fiberglass / Poly (single layer)	0.83	11 mm woven Poly	0.95
R value: A unit used to measure the effectiveness of thermal insulation.

If you have any questions about using this tool or what it's purpose is, contact us and our greenhouse experts will explain how it works and the benefits of using it.

	Length- in feet
	Width- in feet
	Height - in feet
	Height of Sidewall - in feet

	Area of Greenhouse - This number is used to calculate the minimum BTU output needed for your greenhouse.