Collection: Electric heater

Why Electric Heating Suits a Greenhouse

An electric greenhouse heater holds a set minimum temperature without an open flame, a fuel store or a flue. That combination is what makes it the default choice for anyone with power to the greenhouse, and the reason it is the only type safe to leave running unattended overnight.

Combustion heaters produce water vapour as they burn, which raises humidity in a space where humidity is already the main cause of disease. An electric unit adds none, so the air stays drier and mould has less to work with.

Thermostatic Control

A thermostat is the feature that decides running cost. Without one the heater runs continuously whether the house needs it or not. With one it switches on only when air temperature drops below the level you set, which through a mild winter can mean it runs a fraction of the hours.

Set it to what the plants actually need rather than what feels comfortable. Frost protection means holding around three to five degrees, and that costs far less than holding ten for tender stock. Knowing which you need starts with a maximum and minimum thermometer left in the house for a fortnight.

Sizing the Unit

Output should be matched to the cubic volume of the house, not its floor area. This is the single most common error made when buying, and it goes wrong in both directions: an undersized unit runs constantly without reaching temperature, while an oversized one cycles and costs more than it needed to.

• Measure length, width and average height to get volume rather than footprint.
• Allow more output for glass than for twin wall polycarbonate, which insulates better.
• A house with gaps at the base or missing glazing clips will lose heat faster than its size suggests.

Fan Models and Air Movement

Fan assisted heaters distribute warmth rather than letting it collect at the ridge, and the moving air also reduces the still, damp pockets where botrytis starts. Many can run the fan alone in summer, which makes the unit useful year round rather than for four months.

If you need circulation without heat, a dedicated greenhouse fan does the job more cheaply.

Installation and Safety

Greenhouses are damp environments with a hard floor and a lot of glass. Any electrical supply should be installed by a qualified electrician, protected by an RCD, and rated for outdoor use. Extension leads run from the house are not a substitute.

Site the unit clear of staging, foliage and anything hanging, on a level surface where airflow around it is not blocked.

Reducing What You Need to Heat

Insulating first costs less than heating more. Bubble sheet lining the inside of the glazing from the protection range cuts heat loss substantially without blocking the light winter crops still need. Many growers also heat only a partitioned section rather than the whole volume.

Where there is no power at all, the wider heater range covers paraffin and bioethanol alternatives, with the caveat that neither is thermostatic.