Greenhouse heat loss calculator
Glass is a terrible insulator, so greenhouse heat loss is dominated by the glazing area.
W/(m2 K)
Single glass 5.8; twin-wall polycarbonate 3.5; single polythene 6.5.
degrees C
degrees C
per kWh
Heater size needed
8.746kW
- Heat loss
- 8746 W
- Glazed surface area
- 116.00
- Daily energy
- 104.96 kWh
- Daily cost
- 29.39
- Monthly cost
- 894.49
- Heat loss per square metre of floor
- 219 W/m2
Show the working
- Length = 10
- Width = 4
- Average height = 2.5
- Glazing U-value = 5.8
- Inside temperature = 15
- Outside temperature = 2
- Heating hours per day = 12
- Energy price = 0.28
- floor_area = 10 * 4 = 40
- Glazed surface area = 2*(10*2.5) + 2*(4*2.5) + 10*4*1.15 = 116
- dt = 15 - 2 = 13
- Heat loss = 116 * 5.8 * 13 = 8746.4
- Heater size needed = 8746.4 / 1000 = 8.7464
- Daily energy = 8.7464 * 12 = 104.957
- Daily cost = 104.957 * 0.28 = 29.3879
- Monthly cost = 29.3879 * 30.4375 = 894.494
- Heat loss per square metre of floor = 40 > 0 ? 8746.4 / 40 : 0 = 218.66
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- heat loss = glazed area x U-value x temperature difference
Thermal screens and bubble wrap can halve the loss and are far cheaper than the heat they save.
The roof factor of 1.15 approximates a pitched roof over the footprint.