Show the formula and working
This greenhouse heater running cost calculator shows what an electric greenhouse heater costs per night, per month and over a winter. Enter the heater power in kW, how many hours a night it is switched on, the share of that time the thermostat keeps it heating and how many nights a year you use it. It starts with the UK price cap unit rate, has EU presets, and you can type your own tariff.
Quick answer: An electric greenhouse heater costs its power in kW times the hours it is actually heating times your unit rate. A 2 kW heater switched on for 12 hours a night and heating 30% of that time uses 7.2 kWh, about £1.90 a night at 26.32p. Over 100 nights that is about £189.50.
How Is Greenhouse Heater Running Cost Calculated?
Multiply the heater power in kW by the hours it is switched on and by the share of time the thermostat has it heating. That gives the kWh per night, which you multiply by your unit rate.
Electric greenhouse heaters are usually fan heaters or tubular heaters with a thermostat. With the thermostat set just above freezing, the heater only runs on the coldest part of the night, so it draws power for a small share of the time. On a mild night it may barely run at all, and in a hard frost it may run for hours. The heating share is the biggest unknown, which is why the calculator lets you change it. The 30% default is only an example.
How Do You Use the Greenhouse Heater Calculator?
- Enter the heater power in kW from its label.
- Enter how many hours a night it is switched on.
- Set the share of that time it is actually heating.
- Enter how many nights a year you heat the greenhouse.
- Choose a price preset or enter your unit rate.
How Much Does It Cost to Heat a Greenhouse?
At 26.32p per kWh, a 2 kW heater costs about 53p for every hour it is actually heating, so the thermostat setting and insulation matter more than anything else.
| Heating share | kWh per night | Cost per night | Cost per 100 nights |
|---|---|---|---|
| 10% | 2.4 | £0.63 | £63.17 |
| 20% | 4.8 | £1.26 | £126.34 |
| 30% | 7.2 | £1.90 | £189.50 |
| 50% | 12 | £3.16 | £315.84 |
The 26.32p unit rate is the Ofgem price cap average for October to December 2026. You can check the latest figure on the Ofgem energy price cap page.
What Temperature Should a Greenhouse Be Kept At?
Most people only heat a greenhouse to keep it frost free over winter, which uses far less energy than keeping it warm.
Each extra degree on the thermostat makes the heater run for longer, especially on cold, clear nights. Keeping just one section warm for tender plants, using a heated propagator for seedlings or moving the most tender plants indoors can cut the cost a lot. A thermometer that records the lowest overnight temperature helps you set the thermostat no higher than you need.
How Can You Cut Greenhouse Heating Costs?
The cheapest heat is the heat you keep in.
- Line the inside of the glass with bubble insulation for winter.
- Seal gaps around doors, vents and panes.
- Partition off a small area with insulation and heat only that.
- Set the thermostat to the lowest temperature your plants need.
- Place the thermostat away from the heater’s air flow so it reads the real air temperature.
- Use a heater with a reliable thermostat rather than a fixed setting.
To compare with heating a room in the house, the electric heater running cost calculator uses the same method.
Worked Example: A 2.8 kW Heater in a Cold Winter
Example: a gardener uses a 2.8 kW electric fan heater, switched on 14 hours a night for 120 nights. The thermostat keeps it heating about a quarter of the time. The unit rate is 26.32p.
- Per night: 2.8 kW x 14 h x 25% = 9.8 kWh
- Cost per night: 9.8 kWh x 26.32p = £2.58
- Per month of 30 nights: about £77.38
- Per winter: 120 nights x £2.58 = £309.52
In a winter like this, a layer of bubble insulation on the glass and a smaller heated area for the most tender plants could bring the heating share down noticeably, and each 5% cut in heating share saves about £62 over the same 120 nights.
Safety With Greenhouse Heaters
Water and electricity need extra care in a greenhouse.
- Use a heater designed for greenhouse use.
- Use a suitable outdoor supply with RCD protection, installed by a qualified electrician.
- Keep the heater and cables away from water and watering cans.
- Never use indoor plug in heaters on extension leads in a damp greenhouse.
Greenhouse Heater Running Cost FAQs
How much does a greenhouse heater cost per night?
A 2 kW heater on for 12 hours and heating 30% of that time costs about £1.90 a night at 26.32p. A milder night costs much less.
Is it expensive to heat a greenhouse?
It can be if you keep it warm. Keeping it just frost free, insulating it and heating only a small area keeps costs low.
How many kW heater do I need for a greenhouse?
It depends on the size, how well it is insulated and the temperature you want. Check the heater maker’s sizing guide for your greenhouse.
Does bubble insulation really help?
Bubble insulation on the inside of the glass reduces heat loss, so the heater needs to run for less of the night.
Is a paraffin heater cheaper?
It depends on fuel prices. This calculator covers electric heaters. Paraffin heaters also add moisture and fumes, so they need ventilation.
Should the thermostat be near the heater?
No. Place the thermostat where it reads the air near your plants, not in the warm air coming from the heater.
Checked October 2026. Source: Ofgem energy price cap. The heating share is an example; use your own figure.