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Greenhouse Heaters

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There's quite a choice of heaters for a greenhouse. Before considering a heater, don't forget to insulate your greenhouse or your costs will spiral and you may well find your greenhouse heater does not cope on the coldest of nights.

What greenhouse heater you choose will depend on what power sources are available. Solid fuel and woodburners require a lot of attention and are so expensive that if you can afford to install them, your gardener will choose the best model for you!

Paraffin Greenhouse Heaters

The traditional paraffin greenhouse heater has a number of advantages.

They are quite cheap to buy
Available in a range of sizes
Fuel is cheap for them so running costs are low
Reservoirs will last over a day on many models so they don't require too much attention.
They output CO2 so improving growing conditions for your plants
Self-contained, they don't require any electric supply.

They also have some drawbacks:

Fuel may be hard to find nowadays as paraffin is not as popular fuel as it once was
They are always on and manually controlled so can be burning away when their heat is not needed and wasting fuel.
They output water vapour, which can encourage mould in the greenhouse.

Super Warm 5 Paraffin Heater

This large twin burner unit is ideal for use in greenhouses up to 5m² (6'x8') or as an anti-frost heater in larger structures. The fuel capacity is 4.5 litres which will burn continuously for 3½ days

More Information from Harrod Horticulture

Electric Greenhouse Heaters

These are great if you have a power supply to your greenhouse and have some distinct advantages over paraffin heaters. Because they can be thermostatically controlled, heat is delivered only when required so running costs need not be as high. Obviously electricity and water do not mix, so care is required and electric heaters suitable for use in greenhouse are somewhat more expensive than a heater for the house.

A fan heater has the benefit of not just warming the greenhouse but also moving the air around avoiding cold spots and the fungal problems associated with stale air. For low-level background heat, cheap, low-output tubular heaters can be bought for reasonable cost and even connected via a thermostat.

I've actually constructed a heater by connecting a 100W light bulb encased in an old tin with holes made in it and a frost thermostat picked up for 50p from a car boot sale. Doesn't really need more knowledge than wiring a plug.

Frost Fighter Electric Heater

These electric heaters will provide the right environment for seedling and propagation in greenhouses or conservatories. Full thermostatic controls, they are splash proof, IPX2 drip proof and the auto-frost stat activates below 5ºC. Two models are available, 0ne with a 2kw capacity and the other 3kw

More Information from Harrod Horticulture

Gas Greenhouse Heaters

These can be run from mains gas or from propane bottles. Thermostatic control and relatively low cost of gas can make these the most economical heating solution but installation of natural gas requires a CORGI registered installer, not cheap.

Conclusion

For a greenhouse without mains power, paraffin greenhouse heaters are the way to go. If you have electricity available a thermostatically controlled fan heater is a good solution but for protracted cold spells, the paraffin heater becomes the most economical solution by far.