How this calculation works
A greenhouse heating budget combines more than its wall transmission. Roof geometry changes exposed area, and replaced air must also be heated. This page separates cover, air-exchange and perimeter terms so one coefficient does not silently stand in for the whole building.
Useful heat = Ucover × exposed area × ΔT + density × cp × volume × ACH/3600 × ΔT + perimeter factor × perimeter × ΔTA worked example
The example’s ten-by-four-metre greenhouse has two-metre eaves and a three-metre ridge. Exposed cover area is about 104.721 m² and internal volume is 100 m³. At U four and a twenty-degree temperature difference, cover loss is about 8.378 kW. One air change per hour adds about 0.671 kW with the entered air properties, before heater efficiency and any perimeter term.
Good to know
Fixed steady sensible balance only; no solar, storage, latent humidity, wind model, controls or equipment approval. Use actual cover and leakage information and an appropriate design-weather method when selecting a real heating system. Example inputs are illustrative, not recommended settings.
Reference: Alabama Cooperative Extension — greenhouse heat losses (opens in a new tab) ↗
What the model answers
A greenhouse heating budget combines more than its wall transmission. Roof geometry changes exposed area, and replaced air must also be heated. This page separates cover, air-exchange and perimeter terms so one coefficient does not silently stand in for the whole building.
The geometry is a straight gable greenhouse with rectangular walls and triangular end gables. Ground-floor area is not added as another cover surface; an optional entered perimeter-loss factor treats that separate boundary approximately.
The Layered wall thermal resistance calculator builds an ideal U value from supplied layers. A greenhouse’s complete demand additionally needs exposed geometry, air exchange and any separately justified perimeter term.
Measure and enter consistently
Ridge height must be at least eave height. The roof slope follows the half-width and ridge rise, which determines the true roof area rather than using only the plan area.
Cover U should describe the intended assembly and surface effects. Air exchange, density, heat capacity and perimeter factor are entered assumptions. Avoid putting the same air leakage or radiation allowance in more than one term.
Interpret the result
Useful thermal demand is divided by heater efficiency to estimate input power. Multiplying by entered hours assumes those exact indoor and outdoor conditions persist for the whole duration; it is not an annual-weather simulation.
The model requires indoor temperature at least outdoor temperature. It does not add solar gain, thermal mass, humidity condensation or active ventilation controls. Real peak sizing and seasonal energy can differ from this steady scenario.
Work through the numbers
The example’s ten-by-four-metre greenhouse has two-metre eaves and a three-metre ridge. Exposed cover area is about 104.721 m² and internal volume is 100 m³.
At U four and a twenty-degree temperature difference, cover loss is about 8.378 kW. One air change per hour adds about 0.671 kW with the entered air properties, before heater efficiency and any perimeter term.
Where this model stops
Fixed steady sensible balance only; no solar, storage, latent humidity, wind model, controls or equipment approval.
Use actual cover and leakage information and an appropriate design-weather method when selecting a real heating system. Example inputs are illustrative, not recommended settings.
A few questions, answered
Why does ridge height change both terms?
It changes sloping roof area and triangular upper volume, affecting both cover and air-exchange losses.
Are the energy results annual bills?
No. They cover only the entered number of hours at unchanged boundary conditions.