Greenhouse Heating Calculator
Calculate the BTU or kW heater size needed for your greenhouse based on volume, target temperature, and outside temperature.
Heater Size Needed
Greenhouse heating requirements depend on volume, temperature difference, and insulation.
Metric formula:
Heat Loss (W) = Volume (m³) × Temp Difference (°C) × Heat Loss Factor
kW needed = Heat Loss / 1000
Imperial formula:
Heat Loss (BTU/hr) = Volume (ft³) × Temp Difference (°F) × Heat Loss Factor
Heat loss factors by covering material:
- Single glass/plastic: 1.0 (metric) / 1.1 (imperial)
- Double glass/polycarbonate: 0.65 / 0.7
- Triple wall polycarbonate: 0.5 / 0.55
Typical target temperatures:
- Frost-free: 2–5°C (36–41°F) — protect from freezing
- Cool greenhouse: 7–10°C (45–50°F) — overwintering
- Warm greenhouse: 13–18°C (55–65°F) — tropical plants
Note: These calculations assume worst-case nighttime temperatures. Actual needs may be lower with solar gain during the day.