Greenhouse Heater Calculator

How To Calculate How Much Heat A Greenhouse Needs?

So, how much heat will your greenhouse need during winter This is a question you have to first answer before introducing a heater into your structure….and that’s where a greenhouse heater calculator comes in.

The secret here lies in figuring out the number of BTUs required to sufficiently heat the space.

As you may know, these calculations are so crucial.

Otherwise, chances of installing an improperly sized heating device are high.

And you know what that means: potentially big losses in harvest and damaged plants.

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What You Need while making greenhouse heating calculations

To begin our greenhouse heating calculations, we will need some basic data:

  • The size of the target greenhouse
  • The lowest outside temperature (expected in your area)
  • The lowest temperature you intend to maintain in the greenhouse.

The Steps

Well, these calculations are pretty simple.

Here are the rest of the steps

Step I: Finding the Greenhouse Surface Area

Start by capturing the following data

  • Height of your greenhouse(=H)
  • Length of your greenhouse(=L)
  • Width of your greenhouse(=W)
  • Height to the ridge(=R)
  • Length of  the roof slope(=S)

Now find your green house’s surface area (S.A.) as follows:

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

Let’s assume your answer comes to 600 square feet.

Step II: Temperature differences

The next step in this greenhouse heating calculation is to find what we call temperature differences (for lack of a better word)

Here you take the ideal temperature you need in your greenhouse then subtract from this the lowest temperature possible in the region where your greenhouse is located.

For example:

Assuming you need a temperature of 70 °F& the lowest possible exterior temperature is 30 °F, you would get this…

Ideal greenhouse temperature: = 70°F

Coldest outside temperature:   = (30°F)

= 40°F


Step III: Calculate the BTUs

Now, to get the BTUs, you’ll need to multiply your surface area by the temperature difference:

i.e.BTUs =Greenhouse Surface Area X Temperature differences

Using the figures in our example, you would get 600 x 40 = 24,000 BTU’s

Your heater will, therefore, require 24,000 BTU’s to adequately warm your greenhouse.

And so, 24,000 BTU’s would be my magic figure when shopping for a greenhouse heating system!

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Other Influencing Factors that will affect your greenhouse heating calculations

The following variables will affect your calculations:

  • Glazing

Some glazing materials are better. For example, if your greenhouse is built with polycarbonate or double glazed glass, your heat requirement will be 30% less

This means it’s safe to take 30% of your BTU value as your heating requirement.

  • Walling Material

Walls made of brick or cement barely lose heat.

Thus, if that’s the walling in your greenhouse,you will need to go back to your surface area calculation stem and reduce it by ½..

Yeah. That’s right.

For step iii, take ½of your surface area value.

So, if my greenhouse is made of cement, my BTU value would be: (½ of 600)= 300 x 40 = 12,000 BTU’s !

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Expert Greenhouse Heating Tips

  • Always repair any cracks or openings in the insulation to avoid cold air from sneaking inside during frost.
  • You can add insulation in an inexpensive way by lining the interiors of your greenhouse with quality plastic sheets.  This also saves on your overall heating costs.
  • A layer of horticultural fleece can further protect your plants on extremely cold nights. That way, you won’t overwork the thermostat
  • Use a thermostat saves money and energy as it puts off the heater during daytime or when temperatures normalize.


A greenhouse heater calculator enables you to accurately determine the heat output your greenhouse heater must have to adequately warm your plants.

This will help you avoid the losses that arise with insufficient warming, for example, lower yields and huge energy costs.

And as you have seen, the steps are so basic.

So, try it and let us know if it helps!

Click Here For The Best Greenhouse Heaters


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