Free Greenhouse Heater & Heat Loss Calculator
Determine heating requirements in BTU/hr and Kilowatts to keep seedlings alive through freezing winter nights based on glazing thermal U-values.
🏡 Greenhouse Dimensions & Temperatures
🔥 Required Heater Capacity
Recommended Tools & Equipment
Tested hardware and components for high reliability
The Greenhouse Heat Loss Equation
A greenhouse loses heat in two ways: conduction through the glass or polycarbonate panels, and infiltration (air leakage through seams and vents). The fundamental thermodynamic heat transfer formula is:
Understanding the U-Value
The U-value is the overall coefficient of heat transmission. Lower numbers mean superior insulation. Single-pane glass has a poor U-value of 1.13, whereas 10mm triple-wall polycarbonate cuts heat loss by more than half ($U = 0.50$).
Electric vs Propane Heating
Standard household electric outlets in North America supply 120V 15A, limiting electric space heaters to 1,500 Watts (5,120 BTU/hr) each. For large greenhouses requiring > 15,000 BTU/hr, a dedicated 240V circuit or thermostatically controlled vented propane heater is essential.
Frequently Asked Questions
What minimum night temperature should I target in winter?
To simply prevent frost damage on hardy crops (brassicas, lettuce, root vegetables), 38°F to 40°F (4°C) is sufficient. For warm-weather starts (tomatoes, peppers, tropicals), maintain at least 50°F to 55°F (10°C - 13°C).
How do I calculate the total surface area of an A-frame greenhouse?
Add the two side walls ($2 \times L \times H$), the two roof panels ($2 \times L \times \text{Rafter Length}$), and the two triangular end gable walls ($2 \times [W \times H + 0.5 \times W \times \text{Gable Peak}]$).
Can bubble wrap insulation reduce greenhouse heat loss?
Yes! Adding a layer of large-bubble horticultural wrap against single glass or thin polycarbonate reduces heat loss by up to 40%, lowering your heating bill significantly.