Greenhouse Heating Calculator
Heater size to hold your target temperature.
Enter your values
ⓘ Live results
Results
- Heater size needed
- 4.38 kW
- In BTU/h
- 14,961
- Temperature lift
- 18 °C
- Nightly cost at $0.25/kWh
- $13.15
Quick answer
Greenhouse heat demand depends on surface area, glazing U-value and the inside-outside temperature difference.
Watts = area × U × ΔT
How to use the Greenhouse Heating Calculator
- 1Calculate the total glazed surface area.
- 2Pick your glazing type.
- 3Enter target and coldest outside temperatures.
Worked example
Using the values the calculator loads with:
Inputs
- Surface area42 m²
- GlazingSingle glass
- Target inside temp15 °C
- Coldest outside temp-3 °C
Results
- Heater size needed4.38 kW
- In BTU/h14,961
- Temperature lift18 °C
- Nightly cost at $0.25/kWh$13.15
Frequently asked questions
Should I add bubble wrap?
Yes — internal bubble insulation can cut heat demand by a third.
Does soil store heat?
Yes, thermal mass such as water barrels smooths overnight swings.
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.