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Greenhouse Heating Load Calculator

Calculate BTU heating requirements for greenhouses based on floor area, glazing type, target temperature, and outdoor climate.

Use this result well

Inputs that matter
Greenhouse Floor Area, Temperature Difference, Heat Loss Factor
Output to expect
Greenhouse Heating Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Heat loss through envelope

Loss depends on surface area, U-value of glazing, and temperature difference between inside and outside.

BTU/hr ≈ U × area × ΔT

Infiltration and doors

Air leaks and frequent door openings add load. Vented poly houses lose more heat than double-wall polycarbonate.

Safety and recovery margin

Add 10% to 25% margin so the heater can recover after a cold snap or windy night.

Updated: July 2026

Example Scenarios

Compare heat load at 45°F inside when outside drops to 15°F in USDA zone 5.

See how better glazing cuts BTU needs and heater cost over a season.

Model lower night temperatures to right-size heaters for frost protection only.

Common Mistakes to Avoid

Sizing for average winter temp only

Design for the lowest expected night temperature plus wind, not the monthly average.

Ignoring wind exposure

Open fields and ridge-top sites increase infiltration loss. Add margin or use windbreaks.

FAQ

It varies widely. Uninsulated single-layer poly in cold climates may need 30 to 60+ BTU/hr per sq ft of floor area; insulated structures need less.

Air heaters protect foliage and maintain growth. Root-zone heat can reduce air temperature targets for some crops.

Water barrels store daytime heat and smooth night swings. They reduce peak load but do not eliminate heater sizing.

Propane delivers high BTU in cold rural sites. Electric is cleaner and simpler where power is affordable and outages are rare.

Use vented or rated greenhouse heaters. Unvented combustion indoors can kill plants and people.

About Greenhouse Heating Load Calculator

Size a heater before cold nights arrive. Enter greenhouse dimensions, insulation, and temperature targets to estimate heat loss and required BTU output.