Garden planning
Greenhouse Heater Calculator
Estimate design-day heating capacity and electricity use for a freestanding greenhouse.
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Enter a US ZIP code for its USDA hardiness zone and location-specific planning guidance.
Your estimate will appear here
Enter your project details and calculate for a practical planning estimate.
How this estimate works
- • Envelope area is estimated as four vertical walls plus a flat-equivalent roof: 2LH + 2WH + LW.
- • Surface heat loss equals area × glazing U-factor × indoor-to-outdoor temperature difference.
- • Capacity applies the selected safety factor; electrical use converts BTU/hr to watts using 3.412 BTU/hr per watt.
Before you begin
- • This is a steady-state design estimate, not a live weather forecast or a heating-load certification.
- • It excludes air leakage, ground loss, solar gain, wind effects, thermal mass, and non-flat roof geometry.
- • Actual run time and cost can vary substantially with weather, controls, and heater efficiency.
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