Part of the Agriculture collection — 4 tools available
Greenhouse Heating Calculator
Calculate the heating requirements for your greenhouse. Enter size, desired temperature rise, and glazing type to estimate BTU/hr and monthly heating cost.
About This Calculator
Keeping a greenhouse productive through winter requires the right-sized heater — too small and your plants freeze during cold snaps, too large and you waste money on both the equipment purchase and ongoing fuel costs. Greenhouse heating demand depends on the total surface area (not just floor space), the temperature difference between inside and outside, and the insulating value of your glazing material. Single-layer polyethylene film has a high heat loss factor, while double-poly and polycarbonate panels retain significantly more heat. Our greenhouse heating calculator estimates BTU requirements.
The Formula Behind This Calculator
Floor area = Length * Width Volume = L * W * Height Heating BTU = Volume * Temp diff * 0.133
Understanding the math helps you verify results and make better decisions for your project.
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How to Use
- 1Enter greenhouse length, width, and average height in feet.
- 2Enter the temperature rise needed (desired inside temp minus minimum outside temp).
- 3Set the heat loss factor based on your glazing material.
- 4Enter your natural gas price per therm.
- 5Click Calculate for BTU/hr and estimated monthly heating cost.
When to Use
- →Choosing the right greenhouse heater size before purchasing to avoid undersized or oversized equipment
- →Estimating winter heating costs to decide whether greenhouse growing is economically viable
- →Comparing heating costs between single-poly, double-poly, and polycarbonate greenhouse coverings
Tips
- ✓Size your heater 20% above the calculated BTU to handle unexpected cold snaps without running at full capacity
- ✓Add thermal mass like water-filled barrels to store daytime heat and reduce nighttime heating demand
- ✓Seal every gap and use weatherstripping on doors — even small drafts can increase heating costs by 15-25%
FAQ
What size heater do I need for a small greenhouse?
An 8×12 hobby greenhouse typically needs 10,000-20,000 BTU/hr depending on climate and glazing. Always size up 20% from the calculated minimum.
Which greenhouse covering retains the most heat?
Double-layer poly with an air inflation gap reduces heat loss 30-40% vs single poly. Twin-wall polycarbonate and double-pane glass are also excellent insulators.
How can I reduce greenhouse heating costs?
Use thermal mass (water barrels) to store daytime heat, add a second glazing layer, seal all gaps, use a thermostat, and consider a heat pump for efficiency gains.
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