Heating and Cooling

Published on November 19th, 2012 | by Shelley Awad


Calculating BTU’s Required for Heating

How to Calculate BTU’s Required to Heat Your Greenhouse

Heating your greenhouse is necessary if you live in a cold climate area.  Before the first frost of the season, check and secure the insulation and make sure to repair any cracks or holes that may let the cold air inside.

You can also line the interior of your greenhouse with plastic sheeting.  This is an inexpensive way to add additional insulation which will also save on your heating costs.

To calculate the BTU’s (British Thermal Units) required to heat your greenhouse use the simple math formula below:

H  =  height

L  =  length

W =  width

R  =  height to ridge

S  =  length of  roof slope

To calculate the total surface area of the inside of the greenhouse, use this formula:

[2 x (H + S) x L] + [(R+H) x W] = S. A.

Let’s assume that the calculation above results in an answer of 500 square feet. The next step is to determine the “temperature differences” by taking the ideal temperature that you will need in the greenhouse and subtract from it the lowest possible temperature in the area where you live. For example:

Ideal greenhouse temperature =  60 degrees F     Minus

Coldest outside temperature    =  10 degrees F


                                                Equals  50 degrees F

The next step is to multiply the surface area of the inside of the greenhouse x  the temperature difference:

500 x 50 = 25,000 BTU’s

Your greenhouse will need 25,000 BTU’s to heat it properly.

Variables to consider in your calculations include the following:

  • If you have walls that are solid like brick or cement, they will lose less heat so you will only calculate ½ the result of the surface area calculation.
  • If your greenhouse has double glazed glass or polycarbonate, calculate 30% less in the heat requirement


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About the Author

Greenhouse Consultant, Shelley Awad, provides everything you need to know about greenhouses. Whether you are buying a greenhouse or you already own one, you’ll learn tips and tricks on greenhouses and how to grow year-round. Questions always welcome.

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