Free tool
Greenhouse heater running cost
Put in your heater's watts and how long it runs, and see what it costs a night, a week and a winter at today's electricity price.
On the heater's label or in its manual. 2,000 W is just an example: check yours.
On a thermostat a heater only runs when it's cold, so this is usually far less than the hours of darkness. 4 is an example.
An example to change. A max/min thermometer tells you how many nights your greenhouse actually dips that low.
Starts at the Ofgem price-cap rate for 1 October to 31 December 2026. Your bill shows your own rate.
Running cost per night
£2.11
8.0 kWh a night (2,000 W × 4 h)
A week of cold nights
£14.74
A winter (60 nights)
£126.34
The sum is watts ÷ 1,000 × hours × unit rate. It assumes the heater runs at full power for the hours you enter; a thermostat that cycles on and off is already covered by entering fewer hours. Bubble insulation, a thermostat set just above freezing and heating only the part of the greenhouse you use all bring the hours down. The default rate is the Ofgem price cap for 1 October to 31 December 2026 (checked 18 October 2026).
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Protect it: what each cover is for
Most gardens need only fleece and a sheltered spot for pots. The rest earns its place if you grow under glass. Each one links to the guide that explains when it works.
Horticultural fleece
Thrown over plants on a frosty night, it holds in some of the ground's warmth. Light enough to leave on for a cold spell.
How to protect plants from frost →AdFrost fleece, by the metre — Elixir Garden Supplies
Cloches
A rigid cover for a single plant or a short row. It stays put in wind, and you lift it off on mild days.
How to protect plants from frost →Greenhouse bubble insulation
Lines the inside of the glass to slow heat loss at night, so an unheated greenhouse stays a little warmer and a heated one costs less to run.
Heating a greenhouse in winter →AdGreenhouse bubble insulation, 1.5 m wide — Elixir Garden Supplies
A greenhouse heater
Only needed if you're keeping tender plants under glass. On a thermostat set just above freezing, it runs only on the coldest nights.
Heating a greenhouse in winter →Ad2 kW electric fan heater (TSE-20A) — Elixir Garden Supplies
A max/min thermometer
Records the coldest point each night, so you know how cold your greenhouse or cold frame really gets before you spend on heating.
Heating a greenhouse in winter →
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How to use it
Type in your heater's power in watts (it's on the label), how many hours a night it actually runs, and how many cold nights a winter you expect to need it. The cost updates as you type. The electricity rate starts at the Ofgem price cap for 1 October to 31 December 2026; if your tariff is different, put your own rate in from your bill.
The hours are the figure most people get wrong. A heater on a thermostat switches itself off once the greenhouse is warm enough, so on most nights it runs for a fraction of the hours of darkness. If you're not sure, a plug-in energy monitor between the socket and the heater tells you exactly how many kWh it used overnight.
How the sum works
Electricity is sold by the kilowatt-hour: one kilowatt running for one hour. So the cost is the heater's watts divided by 1,000, times the hours it runs, times the price of a kWh. That's all this calculator does, so you can check it by hand. It doesn't estimate how much heat your greenhouse loses; that depends on its size, glazing, shelter and how warm you keep it. For what keeps those hours down, read heating a greenhouse in winter.
Frequently asked questions
- How much does it cost to run a greenhouse heater?
- Multiply the heater's power in kilowatts by the hours it actually runs, then by your electricity unit rate. At the Ofgem price-cap rate for 1 October to 31 December 2026 (26.32p per kWh), a 2 kW heater costs about 53p for every hour it runs at full power. On a thermostat set just above freezing it runs far fewer hours than the night is long.
- Do I need to heat my greenhouse in winter?
- Only if you're keeping tender plants in it. Hardy winter salads, garlic in modules and overwintering broad beans are fine in an unheated greenhouse, with fleece on the coldest nights. Heat earns its keep for pelargoniums, fuchsias, citrus or chillies you want to keep alive until spring.
- How can I cut the cost of heating a greenhouse?
- Line the glass with bubble insulation, set the thermostat just above freezing rather than warm, and heat only part of the greenhouse by curtaining off one end. A max/min thermometer shows how often it actually gets cold enough to need heat.