Gardenia Organic

Greenhouse Heating, BTU and Operating-Cost Calculator

Greenhouse heating calculator

Estimate heat loss, heater output and operating costs using your structure and energy assumptions.

1. Structure and units

Geometry estimates exclude the floor. Hoop roofs use a half-ellipse; lean-to estimates include all enclosing walls. The 26 × 10 ft twin-wall polycarbonate arch uses 317 × 118 in, an assumed 93 in ridge and zero straight sidewall. Confirm your own dimensions; this is not a verified model-specific preset.

2. Glazing and design temperatures
3. Energy-cost scenario

Use your local currency consistently. Convert fuel prices to cost per input kWh. Runtime means equivalent hours at the full design load; monthly cost uses 30 identical nights. The sensitivity range is your selected scenario, not a statistical confidence interval.

JavaScript enables calculations and share links. The formulas and worked example below remain readable without it. Shared inputs stay in the URL fragment.

Enter your measurements, then select Calculate.

Your estimate

Envelope area and air volume
—
Temperature difference and U-value
—
Conduction heat loss
—
Air-exchange heat loss
—
Required thermal output
—
Heater output with +15% margin
—
Fuel / electricity input power
—
Selected sensitivity range
—
Estimated cost per night
—
Estimated cost per 30 nights
—

Formula and worked example

Conduction: Q = U × envelope area × ΔT. Example: 100 m² × 3 W/m²K × 20 K = 6,000 W conduction only, before air exchange or other losses.

Air exchange: Q = 1.2 kg/m³ × 1,005 J/kgK × ACH × air volume × ΔT ÷ 3,600. Thermal output is conduction plus air exchange. Input kW = output kW ÷ efficiency. Cost = input kW × equivalent full-load hours × tariff. 1 W = 3.41214 BTU/hr; 1 imperial U = 5.67826 W/m²K.

The +15% margin is shown separately from the modeled operating cost. Solar gains, ground losses, changing weather and thermal bridges are not included. This estimate does not size wiring or certify heater suitability.

U-values: Palram twin-wall panel data (4/6/8/10 mm: 3.8/3.5/3.3/2.9 W/m²K); Texas A&M glazing and air-exchange estimates (single/double film: 1.15/0.70; single/double glass: 1.13/0.65 imperial U). Glass estimates are generic glazing values, not product-specific tempered-glass certification. Use the supplier’s whole-system U-value when available.

Read the winter greenhouse heating guide or open the standalone heating calculator.

All gardening tools

Latest Posts