How to heat a greenhouse

How to heat a greenhouse

John, Passionate gardener, Cambridge

Guide written by:

John, Passionate gardener, Cambridge

Most home greenhouses aren't heated but it's worth remembering that these structures only raise temperatures by a few degrees in the winter. If you're looking to sow seeds early, grow tropical plants or simply battle very cold weather, you'll need a greenhouse heater. Read on to find out how to heat your greenhouse.

Important features

  • Insulation
  • Electric greenhouse heaters
  • Paraffin greenhouse heaters
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Insulating a garden greenhouse

Heating a greenhouse is only economically viable if the structure is well-insulated. Even if your garden greenhouse is made of an insulating material – such as double walled polycarbonate sheets or double pane glass – it is still possible to increase the temperature by a few degrees by lining the interior walls and roof with bubble wrap. This extra layer can be attached to the frames using special clips. Triple layer bubble insulation has significantly higher insulating power than low-end alternatives, and is also much more resistant.

Bear in mind that not all plants have the same temperature requirements. For this reason, some gardeners choose to set up two small greenhouses instead: an unheated greenhouse, with little or no heating for cold-hardy plants, and a heated greenhouse kept at a much higher temperature (around 10°C or even 15°C).

Electric vs. paraffin greenhouse heaters

Paraffin heaters

These smaller heaters are primarily used to heat small greenhouses of up to 5 square metres and so-called cold greenhouses.

This type of heating works to keep frost at bay and maintain a minimum temperature overnight. Paraffin heaters can also be brought out in extremely cold conditions.

Be sure to only use low-sulphur paraffin (also known as kerosene) as other fuels may produce toxic emissions to plants.

Electric heaters

Various types of specially designed electric heaters can be used in greenhouses including infrared radiators, fan heaters, tubular heaters, and so on.

If you have the option, prioritise systems that promote air circulation. These heaters produce a more even temperature throughout the greenhouse and will heat up the smallest nook and cranny reducing the risk of disease. Some models can even operate on a fan-only mode to ventilate the space during the summer months.

For a small greenhouse measuring just a few square metres, a small electric heater may suffice.

Comparing greenhouse heaters



Paraffin heaters

Easy to set up and move

Economical to operate

Gets rid of water vapour (which promotes disease)

Requires frequent interventions (additional oil needed for back up)

No temperature settings

Requires ventilation

Electric heating

Constant temperature via thermostat 

No condensation

Uniform temperature from floor to ceiling

Easy to move

No gas or smoke emitted

Fan function (no heating) in summer

Effective for large greenhouses (larger than 20 m2) 

Requires electrical outlet

Cost of electrical energy

Dries out air in the greenhouse

Requires back-up heating system in the event of electrical failure

Whatever option you choose, make sure to only use equipment specifically designed for greenhouses. Don't forget to air out your greenhouse on a regular basis. It is a good idea to do so when the weather is warm. Correct ventilation will help to reduce the risk of diseases that thrive in closely confined spaces.

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Alternative greenhouse heating systems

A greenhouse gas heater can be a cost-effective option. However, it is difficult to regulate the temperature with this type of appliance so the greenhouse must be carefully monitored. In addition, gas can emit fumes that are toxic to plants and humans – especially if not regulated correctly. As with paraffin heaters, gas heaters emit water vapour.

Propane gas cylinders are more commonly used as butane freezes as soon as temperatures drop to 0°C.

An old-fashioned alternative heating method involves placing basins of hot water in the greenhouse. This method can still be used as a temporary solution (to deal with excessively low nighttime temperatures, for example) as those extra few degrees can make the world of difference.

A heated propagator for early planting

Early seedlings or delicate cuttings don't require a lot of space and a heated propagator will provide more than enough room. This system consists of a tray with a plastic cover with a heating element in the base.

Alternatively, you can easily make your own propagator using a polystyrene fish box. Simply layer sand at the bottom of the box and install a terrarium heating cable over the top before covering the cable with another layer of sand.

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Guide written by:

John, Passionate gardener, Cambridge

John, Passionate gardener, Cambridge

When I was young, I was already working in the family garden. Perhaps that is where my interest in plants and gardening came from. So, it was logical for me to study plant biology. At the request of various publishers I have, over twenty-five years, written many books on the subject of plants and mushrooms (a subject that is close to my heart). They were mostly identification guides at first, but shortly after they were about gardening, thus renewing the first passion of my childhood. I have also regularly collaborated with several magazines specialising in the field of gardening or more generally in nature. There is no gardener without a garden, I have cultivated mine in a small corner of Cambridge for the last thirty years and this is where I put into practice the methods of cultivation that will I advise you in as well.

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