Room by room
Electric greenhouse heating
The short answer
Greenhouse heating is not about warmth, it is about avoiding a hard frost on a handful of cold nights. Set the target low, insulate first, and the electricity involved is small.
Written and checked by the RapidHeat UK team · Last updated September 2026 · how we work out running costs
Key takeaways
- The goal is usually frost protection at 2–5°C, not a warm room.
- Bubble wrap insulation and a thermostat cut the bill more than any heater choice.
- Electric heat adds no moisture, which is better for plants than paraffin.
Pick a target temperature
| Goal | Minimum temperature |
|---|---|
| Frost free — overwintering hardy fuchsias, geraniums, dahlia tubers | 2–5°C |
| Cool greenhouse — citrus, tender perennials | 7–10°C |
| Warm greenhouse — propagation and early sowing | 13–15°C |
Every extra degree multiplies the cost. Most UK gardeners only need the first row, and a heated propagator handles seedlings far more cheaply than warming the whole structure.
Insulate before you heat
- Line the inside with horticultural bubble insulation — the single biggest improvement.
- Replace cracked panes and seal gaps around the door and vents.
- Group plants together and lift pots off cold staging or paving.
- Use fleece over tender plants on the coldest nights as a second layer.
Wattage guidance
- 6 ft × 4 ft, bubble lined, frost free: 300–500 W with a thermostat
- 8 ft × 6 ft, bubble lined, frost free: 500–1,000 W
- 10 ft × 8 ft or cool greenhouse targets: 1,000–2,000 W
What it costs
A thermostatic heater in a frost-free greenhouse only runs on cold nights, and then only in bursts. A 500 W unit averaging two hours of actual running a night uses about 1 kWh — roughly 27p — and on mild nights nothing at all. Across a winter that is typically tens of pounds, not hundreds. Method in running costs.
Safety and suitability
Greenhouses are damp, and damp plus mains electricity needs care. Purpose-made greenhouse heaters are built with that environment in mind; a domestic room heater is not. If you use one in an outbuilding, it must be kept dry, raised off the ground, well clear of watering and foliage, fed from a properly installed weatherproof supply, and fitted with overheat protection. Never run a heater in a greenhouse where condensation can drip onto it.
Also make sure air can circulate — stagnant, humid air encourages botrytis and mildew, so ventilate on mild days even in winter.
Where RapidHeat fits
RapidHeat is designed as an indoor room heater, so its natural home is a garden office, workshop or the house itself rather than a wet greenhouse. If you want low-cost frost protection under glass, choose a heater specified for horticultural use; for people-heating in a dry outbuilding, see shed and workshop heating.
RapidHeat ceramic heater
4.8/5 · 1,247 UK customers£49.95· £89.91 for two · £110.89 for three (about £36.96 each)
- Thermostat, timer and remote
- Warm room in about 5 minutes
- Free tracked UK delivery
- 30-day money-back guarantee
Perfect for my cold office
I have a small office with a door that gets really cold because the building management keeps the winter temperature far too low for comfort. I plugged this into the socket above my desk and now I am warm without anyone even knowing it is there. I love it.
Great in the bathroom
We use it to take the chill off the bathroom before the kids' bath time. Warms up fast and the timer is handy. Four stars only because I wish the display were a little dimmer at night.
Worth being straight about: RapidHeat is built for rooms up to about 12 m². It is not a replacement for central heating and it will not transform an open-plan lounge or an uninsulated garage. If it is not right for your room, send it back within 30 days.
Questions people ask
- What temperature should a greenhouse be kept at in winter?
- For overwintering most plants, just above freezing — 2°C to 5°C is a common target. Tender plants may need 7°C to 10°C, which costs considerably more.
- How much does it cost to heat a greenhouse?
- It depends entirely on how cold it gets and how well the greenhouse is insulated. A thermostatically controlled 1,000 W heater only draws power when the temperature drops, so a mild week may cost pennies and a hard frost several pounds at 27p per kWh.
- Is an electric greenhouse heater safe?
- Use a heater intended for damp conditions on an RCD-protected outdoor-rated supply, keep it off the floor where water collects, and keep foliage well clear. A standard indoor plug-in heater is not a substitute for a greenhouse-rated unit in wet conditions.
- Can I heat only part of the greenhouse?
- Yes, and it is much cheaper. Partition a section with bubble wrap or fleece and heat only the bench where your tender plants sit.
Warmth where you actually spend time
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