How this calculator works
Extrude the chosen cross-section along the greenhouse length. Add both end walls and exposed sidewalls to the curved or sloping roof. A circular arch uses chord width and rise to determine its radius. Pointed mode joins two equal-radius arcs at the roof centre, with their circle centres on the sidewall line. Inverse modes recover length, covering area, U-value or balance temperature from the same relationships. Heat loss is covering area times the entered U-value and temperature difference. Use the actual covering assembly value, including inflated layers where applicable. This estimate excludes air leakage, floor loss, doors, thermal curtains and solar gains.
Formula
circular radius = width²/(8 x rise) + rise/2; bow = radius x central angle; covering area = roof length x house length + sidewalls + two ends; heat loss = U x area x temperature difference.
Worked example
A semicircular house 4 m wide and 10 m long has 20pi m2 of curved roof and 4pi m2 of ends, for 75.398 m2 covering. With U = 1 and a 10 K difference it loses about 754 W.
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Frequently asked questions
Does this include extra plastic for fastening?
No. The result is geometric covering area. Add overlap, ground burial, end attachment and supplier roll-width allowances separately.
Which pointed arch is modelled?
Pointed mode uses two circular arcs with vertical tangents at the sidewalls. Actual bent-pipe and Gothic greenhouse bows may differ; use measured covering area for those assemblies.
Why is heater input higher than heat loss?
A fuel heater loses some input energy. Dividing by thermal efficiency estimates the required input before other heat-loss allowances.