Greenhouse heater sizing calculator
PROBTU/hr to hold greenhouse temperature on the coldest night.
Short answer: BTU/hr = surface × ΔT × U-value. 400 sq ft × 40°F × 1.1 = 17,600 BTU/hr. Enter your measurements above and the greenhouse heater sizing calculator returns the quantity, unit conversions and an estimated cost instantly, in imperial or metric — no sign-up needed.
What do you need to measure?
What is the answer?
BTU/hr required
17,600
Watts (electric)
5,158
How does the greenhouse heater sizing calculator work?
BTU/hr = surface × ΔT × U-value.
What does a worked example look like?
400 sq ft × 40°F × 1.1 = 17,600 BTU/hr.
What do people ask most?
›Add a safety margin?
Add 20% for wind chill and infiltration.
Which garden calculator should you use next?
Where can you learn more?
Read field notes on estimating and materials, or browse every calculator we make.
What should you read before you order materials?
Field notes from real jobs that explain the numbers behind this calculator.
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