Greenhouse Heating Load Calculator
Calculate BTU heating requirements for greenhouses based on floor area, glazing type, target temperature, and outdoor climate.
Built for Greenhouse1 documented formulaFocused single-task workflowPrivate in your browser
Use this result well
A quick decision brief for this specific tool
Inputs that matter
Greenhouse Floor Area, Temperature Difference, Heat Loss Factor
Output to expect
Greenhouse Heating Calculator
How it works
1 documented formula across 1 calculation mode
- Keep 3 bounded inputs within the limits shown beside the fields.
- Confirm that every value uses the unit and time basis shown before comparing scenarios.
- Change one input at a time to see which assumption materially changes the result.
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Reference & details
How it works
Updated July 2026
How it works
Updated July 2026Heat loss through envelope
Loss depends on surface area, U-value of glazing, and temperature difference between inside and outside.
BTU/hr ≈ U × area × ΔTInfiltration 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
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.