Greenhouse Heating Requirement Calculator

Greenhouse Heating Requirement Calculator

Sizing a greenhouse heater correctly requires knowing how much heat your structure loses through its covering during cold weather - undersizing leaves plants exposed to damaging cold, while oversizing wastes money on unnecessary heater capacity.

Heating Requirement = Surface Area x Heat Loss Factor x Temperature Difference

Example

500 sq ft greenhouse, 65┬░F target, 20┬░F outdoor low, heat loss factor of 1.2:

Temperature Difference = 45┬░F → Heating Requirement = 27,000 BTU/hour

Covering Material Drives Heat Loss

The heat loss factor depends heavily on your greenhouse's covering material - single-layer polyethylene film loses heat much faster than double-layer inflated poly (which traps an insulating air gap) or rigid polycarbonate panels. This is exactly why covering choice directly drives ongoing heating costs in cold-climate greenhouse operations, sometimes justifying the higher upfront cost of better-insulating materials.

Build in a Safety Margin

This calculation sizes a heater to maintain target temperature during your area's coldest expected conditions - real-world heater sizing should include a safety margin above this baseline figure to account for unusually cold snaps, heater efficiency losses, and gradual heat loss through gaps and seams not captured in this simplified surface-area model.