Greenhouse Heating Calculator
Sizes a greenhouse heater to keep it above freezing, or at a set temperature, on the coldest night.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
heat = (U × covering area + 0.33 × air changes × volume) × temperature difference
0.33 Wh/m³K is the heat needed to warm a cubic metre of air by one degree. Soil and floor losses are left out, as are gains from sun.
What to watch out for
Heating only a small section with a bubble-film partition cuts the area and volume at once. Keep the design temperature low unless the crop needs it, because each degree adds to the difference on every surface.
Frequently Asked Questions
What size heater for a 6 × 3 m greenhouse?
Single glazed, at 1 air change per hour, holding 10 °C against −5 °C takes about 5.2 kW.
Does bubble insulation help?
Yes. It lowers the U-value and cuts air leakage, though it also reduces the light reaching the plants.