How much heat a greenhouse loses at night

On a cold night a greenhouse loses heat through its thin glazing in proportion to three things: how easily the covering lets heat through (its U value), how much surface it has, and the temperature difference between inside and outside. The heater has to replace that loss, so a second layer of film with trapped air between can cut the fuel bill by roughly 40 percent.

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Inside setpoint

Outside temperature

Glazing

Step through it

The glazingFilm and glass let sunlight in by day, but they are thin, so heat leaks out through them quickly at night.
Single filmOne layer of polyethylene has a U value near 6.8 watts per square meter per degree, among the leakiest common coverings.
Double filmTwo layers with air blown between them cut the U value to about 4.0, so the same night costs about 40 percent less heat.
The heaterA unit heater burns gas and blows warm air through the house. Its output must at least match the heat loss on the coldest design night.
Design nightGrowers size heaters for the coldest nights they expect. Push the outside temperature to its minimum and watch the load climb.

Q = U x A x ΔT

Heat loss through a covering is the U value times the surface area times the inside minus outside temperature. U values from extension tables, converted to metric, are about 6.8 W/m²·°C for single film, 4.0 for double inflated film, 2.8 for double film with an infrared additive, and 6.4 for single glass.

The model uses a modest freestanding greenhouse with 500 square meters of covering. It leaves out air leaks, wind and ground losses, which can add a lot, so treat the result as the glazing share only.

Try it: set 18 °C inside and minus 10 °C outside, then switch from single film to double film. Heat loss drops from about 95 kW to about 56 kW. Now pick the IR film and see it fall again.

Fuel estimate

The propane readout assumes about 7.0 kWh of heat per liter of propane and a heater that delivers 80 percent of it to the house. Both are rounded assumptions for teaching; your fuel supplier and heater label give real numbers.

Where Avid uses this

Avid's founder began his career as an HVAC apprentice at 16, and heat loss calculations like this one are the starting point of every heating design.

Sources

Calculating Greenhouse Heating RequirementsPurdue University Controlled Environment Agriculture
A Simple and Effective Model for Predicting the Thermal Energy Requirements of Greenhouses in EuropeEnergies, MDPI (open access)

How to cite this model

Avid Solutions International. (2026, November 11). How much heat a greenhouse loses at night [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/greenhouse-heat-loss

Last updated November 11, 2026

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