Greenhouse heaters. Electric, natural gas, propane and many more. But which heater is right for your greenhouse? How do you find out? This is where BTU’s (British thermal units) come in. To find the best heater for your greenhouse you must know the number of BTU’s required. And I am going to show you how to determine it!
Here are a few simple steps to find your BTU requirement.
- STEP 1
You need to know the surface area of your greenhouse. This is not simply multiplying the length and width. You must calculate the area of each wall and each ceiling panel then add them all together. If you have a Sunglo greenhouse click here for Sunglo’s Surface Area Guide post.
- STEP 2
Next you need to find out the average winter temperature (outside) in your area. This is where the internet comes in handy. But I made it easy for you > Click here to view a list of average temperatures in the U.S.
- STEP 3
Now what temperature do you want to keep your greenhouse at in the winter? This depends on the plants you are growing. You should be able to find plant temperatures online. But a common minimum temperature for over wintering is 50°F.
- STEP 4
The next step is finding your greenhouse’s U-Value or Heat Transfer Coefficient. This is determined by the material your greenhouse is made of. For a Sunglo greenhouse we use a U-Value of 0.75. To find your specific materials U-Value > Click here for a general list.
- STEP 5
Now that you have completed the first 4 steps you should have –
- Your greenhouse surface area
- Average winter temperature
- Desired greenhouse temperature for the winter months
- Your greenhouse material U-Value
Now we can find our required BTU’s!
And here is the formula –
- Desired greenhouse winter temp – Average winter temp outside = Temp differential
- Surface area × temp differential × U-Value = Required BTU
My greenhouse surface area is 744
My average winter temp is 20°F
Desired greenhouse winter temp is 50°F
Sunglo acrylic U-Value is 0.75
- 50° − 20° = 30° (Temp differential)
- 744 (surface area) × 30 (temp differential) × 0.75 (U-value) = 16,740 BTU’s
Now you can shop for a heater that provides at least 16,740 BTU’s!