Greenhouse Heater BTU Calculator
Heating load for a greenhouse.
Enter your values
ⓘ Live results
Results
- Heater size
- 22,226 BTU/h
- In kW
- 6.51
- Surface area
- 907 sq ft
- Temperature difference
- 35 °F
- With 15% margin
- 25,560 BTU/h
Quick answer
Greenhouse heat loss is surface area times the U-value of the glazing times the temperature difference.
BTU/h = area x U x ΔT
How to use the Greenhouse Heater BTU Calculator
- 1Enter the greenhouse dimensions and average height.
- 2Choose the glazing and enter your coldest expected night.
- 3Add 10-20% margin, and use a thermal blanket to cut the load sharply.
Worked example
Using the values the calculator loads with:
Inputs
- Length24 ft
- Width12 ft
- Average height8 ft
- Inside target55 °F
- Coldest outside20 °F
- GlazingDouble poly (0.70)
Results
- Heater size22,226 BTU/h
- In kW6.51
- Surface area907 sq ft
- Temperature difference35 °F
- With 15% margin25,560 BTU/h
Frequently asked questions
Vented or unvented heater?
Always vent combustion heaters — unvented units dump moisture and CO2 into the house.
Cheapest saving?
An internal thermal screen at night can cut heat loss by 30-50%.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.