How much does it cost to heat a greenhouse in the UK?
Quick answer
Keeping a 6ft x 8ft single-glazed greenhouse frost-free at 5°C costs roughly £95 in electricity from November to March, based on Ofgem’s October 2026 price cap of 26.32p per kWh. Lining it with bubble insulation brings that down to about £64. Holding 10°C instead costs around five times more.
Almost every answer you find on greenhouse heating costs in the UK is a single number with no working shown, which is useless, because the bill depends entirely on how big your greenhouse is, what it is glazed with, and what temperature you insist on holding. A 6ft x 4ft frame kept frost-free and a 8ft x 10ft glasshouse kept at 10°C are separated by a factor of roughly fifteen.
So this guide shows the arithmetic. You will find the running cost for three common greenhouse sizes at two target temperatures, a month-by-month breakdown of where the money actually goes, and the sizing figures for choosing a heater that is neither underpowered nor wasteful. Every electricity figure uses 26.32p per kWh, the average unit rate under the price cap for 1 October to 31 December 2026.
In this guide
What you are actually paying for
A greenhouse heater is not warming your plants. It is replacing heat that leaks out through the glazing, continuously, all night. The rate of that leak comes down to three things:
- Glazed area. A 6ft x 8ft greenhouse has around 18m² of glazing and frame once you count the roof slopes and gable ends. An 8ft x 10ft has nearly 25m².
- How well the glazing holds heat. Single horticultural glass loses heat at roughly 6 watts per square metre for every degree of temperature difference. Twin-wall polycarbonate is closer to 3.5. Bubble lining over single glass lands somewhere around 4.
- The temperature gap you are holding. This is the one that punishes you. The cost is proportional to the difference between inside and outside, and the number of hours that difference exists. Going from a 5°C target to 10°C does not add 50% to the bill. It adds roughly 400%, because the heater goes from running on a handful of cold nights to running most nights from November onwards.
That last point is the single most important thing on this page. Almost everyone who complains about the cost of greenhouse heaters and thermostats is holding a temperature five degrees higher than their plants actually need.
Running costs by greenhouse size
The figures below model a full UK heating season, November to March, against typical monthly average temperatures and normal day-night swing. They assume a thermostatically controlled electric heater at 26.32p per kWh, and that the heater only runs when the internal temperature would otherwise fall below target.
| Greenhouse | Glazing | Frost-free, 5°C | Growing on, 10°C |
|---|---|---|---|
| 6ft x 4ft | Single glass | 242 kWh — £64 | 1,182 kWh — £311 |
| 6ft x 4ft | Bubble-lined | 162 kWh — £43 | 788 kWh — £207 |
| 6ft x 8ft | Single glass | 363 kWh — £95 | 1,769 kWh — £466 |
| 6ft x 8ft | Bubble-lined | 242 kWh — £64 | 1,179 kWh — £310 |
| 8ft x 10ft | Single glass | 495 kWh — £130 | 2,415 kWh — £636 |
| 8ft x 10ft | Bubble-lined | 330 kWh — £87 | 1,610 kWh — £424 |
Read the 5°C and 10°C columns side by side before you decide anything else. On a bubble-lined 6ft x 8ft, frost protection for the whole winter costs about £64. The same greenhouse held at 10°C costs £310. That is a £246 decision, made by one dial.
Where the money goes, month by month
For a 6ft x 8ft single-glazed greenhouse kept frost-free at 5°C:
| Month | Electricity used | Cost |
|---|---|---|
| November | 19 kWh | £5.06 |
| December | 86 kWh | £22.70 |
| January | 121 kWh | £31.79 |
| February | 101 kWh | £26.62 |
| March | 35 kWh | £9.24 |
January and February account for well over half the season. If your overwintering plants could be moved somewhere sheltered for those eight weeks — a porch, a cold frame against a house wall, a corner of a garage with a window — you avoid most of the bill without buying anything.
A single hard night is cheaper than people fear. Twenty-four hours at −3°C outside, holding 5°C inside a 6ft x 8ft glass greenhouse, uses about 21 kWh — roughly £5.50. Bubble-lined, the same night costs around £3.70. It is the accumulation of ordinary damp 3°C nights, not the dramatic cold snaps, that builds the total.
Comparing the heating options
| Method | How it works | Running cost | Best for |
|---|---|---|---|
| Electric fan heater with thermostat | Heated element plus a fan that keeps air moving, so there are no cold corners | The figures in the tables above; cuts out the moment the target is reached | Any greenhouse with a mains supply; the default choice |
| Electric tubular heater | Low-wattage tube at bench or floor level, gentle convection, no fan noise | Similar per kWh, but needs a separate thermostat or it runs continuously | Frost protection in small greenhouses and lean-tos |
| Heat mats and soil-warming cable | Warms the compost and root zone directly instead of the whole air volume | A fraction of whole-house heating; typically tens of watts, not thousands | Germination and cuttings, not overwintering a full greenhouse |
| Paraffin heater | Wick burner, no electricity needed; burns whether or not heat is required | Around 10 kWh of heat per litre, so 4-litre retail packs at £12–£15 work out dear per kWh | Allotments and sites with no power, where cost per kWh is not the deciding factor |
| Bottled gas heater | Burner fed from a propane cylinder; some models are thermostatic | Divide your refill price by the kWh the cylinder holds; varies widely by supplier | Larger off-grid structures where a cylinder can be sited safely outside |
| Insulation and fleece, no heater | Bubble lining on the glazing plus fleece draped over plants on cold nights | Nothing at all after the initial outlay | Hardy and dormant plants, which is most of what sits in a winter greenhouse |
One difference does not show up in a cost column and matters more than most of them. Paraffin and bottled gas both produce water vapour as they burn, which means condensation on the glass, damp compost and a much better environment for botrytis and other moulds. You have to leave a vent open for safe combustion, and that vent is also letting your heat out. Electric heating keeps the air dry, which is half the point of protecting plants over a British winter in the first place.
Get the control right
The thermostat, not the heater, decides your bill. A heater that holds 5°C accurately will always cost less to run than a more powerful one that overshoots.
Browse heaters and thermostats →Who should heat, and who should not
Heating earns its money when you have plants that genuinely die below freezing: tender fuchsias and pelargoniums, citrus in pots, overwintering dahlias that have not been lifted, or a stock plant you cannot replace. For those, £60 or so over a winter is cheap insurance.
It is the wrong purchase if you are only overwintering hardy plants. Garlic, broad beans, hardy salad leaves, dormant perennials and most overwintering veg do not need a heater at all. An unheated greenhouse already runs a few degrees above the outside air and blocks wind and rain, which is most of the protection those plants need. Adding heat to that is spending three figures to solve a problem you do not have.
It is also the wrong purchase if what you actually want is an early start on seed. Germinating at 18–21°C in a whole greenhouse in February is financially absurd, and the light levels will not support the seedlings anyway. Heat the compost instead. A propagator heat mat warms a seed tray for a few pence a day, and a lidded heated propagator gets you the same germination temperatures on a fraction of the energy. For the plants that only need shelter rather than warmth, horticultural fleece and crop covers do the job for nothing at all per night.
Sizing the heater: wattage by greenhouse
The heater has to be able to replace heat as fast as it escapes on your coldest night. These figures assume a design low of −5°C outside and single glazing. Deduct about a third if the greenhouse is bubble-lined.
| Greenhouse | Glazed area | For 5°C frost-free | For 10°C |
|---|---|---|---|
| 6ft x 4ft | 12m² | 750W–1kW | 1.2–1.5kW |
| 6ft x 8ft | 18m² | 1.2–1.5kW | 1.8–2kW |
| 8ft x 10ft | 25m² | 1.5–2kW | 2.5–3kW |
Oversizing does not increase your running cost as long as the thermostat is accurate — a 2kW heater holding 5°C uses the same energy as a 1.5kW one, it simply runs for a shorter proportion of each hour. Undersizing is the real failure, because the heater runs flat out on the coldest night of the year and still loses the battle. The Vitako range is listed by wattage so you can match it to the table above rather than guessing from a room-size rating written for indoor use.
Before you plug anything in Greenhouse electrics are outdoor electrics. Supply should be on an RCD-protected circuit installed by a qualified electrician, with outdoor-rated sockets kept off the floor and clear of watering. Follow the heater manufacturer’s instructions on clearances and never run one from a domestic extension lead trailed across the garden.
Seven ways to cut the bill
- Line it before you heat it. Horticultural bubble insulation on the inside of the glazing reduces heat loss through the panes and takes roughly a third off every figure in this guide. On a 6ft x 8ft that is about £30 saved over one winter, and the lining lasts several seasons.
- Drop the target temperature. Most overwintering needs 5°C, not 10°C. This is the single biggest lever available to you.
- Heat a bench, not a building. Group tender plants at one end, screen that section off with bubble insulation, and heat the enclosure. You might cut the heated volume by two thirds.
- Seal the draughts. Replace perished glazing clips and door seals, and check for slipped panes. Air leaking out of gaps is heat you have already paid for.
- Get the thermostat off the floor. Mount it at plant height, away from the heater outlet and out of direct sun, or it will read the wrong temperature and run longer than it needs to.
- Insulate the ground under staging. A layer of insulation board or thick membrane under benching slows heat loss into cold soil.
- Still ventilate on mild days. Damp stagnant air causes more winter losses than cold does. Vents open on a bright afternoon, closed before dusk.
Insulation materials, staging and ventilation sundries sit in greenhouse equipment and accessories, alongside the rest of the greenhouse kit Vitako stocks.
Ready to get the greenhouse through winter?
Thermostatic heaters, tube heaters and controllers, listed by wattage so you can size from the table above.
Shop heaters and thermostats →Frequently asked questions
Is it cheaper to heat a greenhouse with electricity or gas?
For most gardeners with mains power, electricity is cheaper in practice and far easier to control. An electric heater switches off the moment the thermostat is satisfied, while paraffin burns continuously whether heat is needed or not. Paraffin bought in small retail packs usually works out dearer per kWh than mains electricity.
How much does it cost to keep a greenhouse frost-free overnight?
On a cold night at around −3°C outside, a 6ft x 8ft single-glazed greenhouse held at 5°C uses roughly 21 kWh over 24 hours, or about £5.50 at 26.32p per kWh. Lined with bubble insulation, the same night costs closer to £3.70. Ordinary mild nights cost a fraction of that.
Do I actually need to heat my greenhouse over winter?
Usually not. An unheated greenhouse already sits several degrees warmer than outside and will overwinter garlic, broad beans, hardy salads and dormant perennials perfectly well. Heat only if you are protecting genuinely tender plants such as fuchsias, pelargoniums or potted citrus, or safeguarding stock you could not replace.
Does bubble wrap really cut greenhouse heating costs?
Yes. Lining the inside of the glazing with horticultural bubble insulation slows heat loss through the panes and takes roughly a third off the running cost in this modelling, about £30 over one winter on a 6ft x 8ft greenhouse. It does cut light slightly, so take it down in early spring.
What temperature should I set my greenhouse thermostat to?
Set it to the lowest temperature your plants will tolerate. 5°C keeps everything frost-free and covers most overwintering. 7°C suits tender perennials. Only go to 10°C if you are actively growing on, and in that case heat a covered bench rather than the whole greenhouse.
Work out your own figure before you buy anything: glazed area, glazing type, target temperature. Then insulate first and size the heater second. When you know the wattage you need, the Vitako heater and thermostat range is listed so you can match it directly, with UK delivery in time for the first frosts.