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Made In Britain Homegrown Company
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The A-Z Of Greenhouse Heating

The A-Z Of Greenhouse Heating

10 minute read


By heating your greenhouse in the colder months you will not only be able to protect tender plants from frost damage, you’ll also open up a whole new realm of winter gardening. However, greenhouse heating can be costly – so we’ve put together these simple tips to make it efficient and cost effective for you to heat your greenhouse.

Automatic temperature control within your greenhouse is easy if you use a greenhouse heater with a built in thermostat. Most electric fan heaters, propane gas heaters and natural gas heaters have built in thermostats. Some electric heaters – such as our Tubular Heaters – don’t have a built in thermostat but can be wired to one to allow you precise temperature control. The more traditional paraffin heaters do not have thermostats built in and cannot be controlled by a thermostat so rely on you to manually turn the heater on and off to maintain a temperature within your greenhouse.

Bottled gas heaters (also known as propane gas heaters) are available in a range of sizes to suit domestic greenhouses. Thermostatically controlled they are an easy way of keeping you greenhouse heated. Modern gas heaters are thermostatically controlled, many have frost stat settings. They are simple to use with push-button ignition and built in safety flame failure device.

Choose the right temperature so you don’t waste energy and money on maintaining a higher temperature than your plants require. If you just need to keep your greenhouse frost free then you can aim to maintain a temperature of 2*C /36*F – in fact most heaters have a frost stat setting on their thermostat to make this simple for you. If you are overwintering tender plants – such as pelargoniums or half hardy fuchsias or protecting young plants or plug plants - then aim for a temperature of approx. 7*C / 45*F.

Distribute warm air evenly throughout your greenhouse by using a fan heater. Circulating warm air throughout the whole of your greenhouse will help to reduce the risk of disease caused by stagnant pockets of air.

Electric fan heaters are both efficient and easy to use to heat your greenhouse. Fan heaters are supplied ready to plug in – there’s nothing else you need to do. Most fan heaters are thermostatically controlled, so you can set the temperature required and the heater will automatically turn on and off to achieve this – so no heat is wasted. The fan within the heater ensures the warm air generated is quickly and evenly circulated throughout the whole greenhouse, so reducing the chance of cold spots.

Frost Stat settings on a greenhouse heater are the simplest way to make sure your greenhouse will remain frost free during the colder months of the year. A Frost Stat setting is designed to turn the heater on and off to maintain a temperature just above freezing – check when buying your heater that a frost stat setting is included, most electric greenhouse fan heaters have this setting.

Gas greenhouse heaters are not only good at heating your greenhouse; the heat also generates growth enhancing carbon dioxide which will benefit your plants.

Heated trays, hot benches, propagators etc can all be used in your greenhouse to provide seeds, seedlings and new plants with bottom heat for healthy germination and growth. These allow you to provide heat exactly where your plants are, so you don’t have to keep the whole greenhouse at a propagation temperature if you are starting seeds off during the autumn or winter months.

Insulate your greenhouse and you’ll reduce heating costs by up to 50%! Even if you decide not to have a heater within your greenhouse, by simply insulating the greenhouse you will be reducing heat loss as well as blocking any draughts, helping to keep your greenhouse frost free. Don’t be tempted to use ordinary bubble wrap as insulation, buy purpose made bubble insulation - such as our heatsheets – which is stronger and has been UV stabilised for long life.

Just plug in an electric heater in your greenhouse and it’s ready to use. This makes electric greenhouse heaters the easiest to use and control. Most electric heaters have a built in thermostat so will automatically turn on and off to maintain a given temperature, so no energy is wasted. And if your electric heater incorporates a fan then it will ensure the heat is evenly and quickly distributed throughout the whole greenhouse.

KW is used when describing the power of a heater. A KW or Kilowatt is equivalent to 1000 watts. You will be familiar with watts being used for lighting – for example a 60 watt bulb. And on your electricity bill you will see how much you are paying per kilowatt of power. So the KW of a greenhouse heater will not only show you the potential power of the heater, it will also enable you to work out the running costs of using the heater.

Low-wattage, electric tubular heaters are ideal for providing a good background heat. Tubular heaters can be used singly, or for more heat set in rows of two or more. Tubular heaters do not have a built in thermostat, so we recommend that you buy a thermostat and wire the tubular heaters to it, so you can then control the heaters turning on and off to maintain the temperature you require.

Mend broken pieces of glass in your greenhouse during the autumn before you insulate your greenhouse to reduce the possibility of draughts. Use our All Weather Tape to quickly and efficiently cover cracks in glass or polythene.

Natural gas greenhouse heaters are designed to run on natural gas. Like propane gas heaters they are thermostatically controlled so no energy is wasted on overheating your greenhouse. Natural gas heaters are great for greenhouse environments as they produce no odour or harmful fumes.

Only heat the area you need to – don’t waste energy and money heating your whole greenhouse if you are only protecting a few tender plants. Ideally group all your plants together and divide that area of the greenhouse off from the rest using bubble insulation to make a dividing ‘wall’. You can then heat just the smaller area where your plants are, so reducing heating costs.

Paraffin heaters are a good option when you have no mains power in your greenhouse. They allow you to heat greenhouses and other out buildings no matter where they are located. Designed to safely and efficiently heat greenhouses, paraffin heaters generate CO2, a main plant food for healthy growth.

Quiet operating fans are the feature of most electric fan heaters. This means that they you could also use the heater in a conservatory where you would want the fan to run quietly.

Roof vents can be used during the colder months to provide some ventilation, so fresh air can get into your greenhouse to help reduce the chance of stagnant air pockets which can result in disease and damage to your plants. If you’re insulating your greenhouse, remember to cut the insulation around the roof vents so that they can still be opened if required – use some All Weather Tape or Double Sided Tape to fix the insulation neatly around the vents.

Save on heating costs by using Garden Fleece in your greenhouse on very cold nights. Simply covering your plants with one or two layers of fleece will provide several degrees of protection so you wouldn’t have to turn the temperature up on your greenhouse heater. Just remember to only cover your plants overnight and remove the fleece during the day, otherwise it would block out too much light reaching your plants.

Thermometers allow you to monitor the temperature within your greenhouse. Choose a thermometer which records the maximum and minimum temperatures achieved. This will help you work out if you are over heating or under heating your greenhouse.

Use a heater that has a built in thermostat. A thermostat allows you to set your greenhouse heater to only come on when the temperature drops below a certain point. In this way no money is wasted on overheating your greenhouse.

Ventilation in your greenhouse is just as important during the colder, winter months as it is during the warmer summer months. By heating your greenhouse you are increasing the opportunity for condensation. If condensation is allowed to build up in your greenhouse it will lead to the spread of fungal diseases amongst your plants. To prevent this provide some form of ventilation during the day in the winter months – even just keeping a louvre window open will allow fresh air to enter your greenhouse and clear condensation - close the louvre again in the evening so your greenhouse will retain any heat provided.

Winter crops can be successfully germinated, grown and harvested in a heated greenhouse. You could plant new potatoes for Christmas dinner. Grow lettuce in growbags or greenhouse beds so you have a fresh harvest all through winter. Bring herbs in pots indoors to keep them cropping longer – you could also plant parsley in the autumn and harvest during winter months.

X marks the spot when it comes to positioning a heater in your greenhouse. You should consider the position of a heater in your greenhouse carefully. You don’t want it placed too close to your plants – if a heater is too close your plants could be damaged by loss of moisture or too high a temperature. If your plants are going to be positioned on benches within the greenhouse then you could place the heater on the floor so that the heat it not pointed directly at them. Some heaters can be suspended from the roof of the greenhouse – these are ideal for busy greenhouses. Ideally position your heater in a central spot, so the heat can spread evenly throughout the area.

You can use a heater in your greenhouse during the colder months of the year so that you can over winter tender plants. This same heater can be used early in the year to lift the temperature in the greenhouse when you are sowing seeds and propagating new plants.

Zero degrees centigrade or 32 degrees Fahrenheit is the temperature at which frost occurs. Frost will damage plants more in the spring as they are putting on new growth. In the winter, however, the plants have become acclimatised to the cold so will not be as badly affected. For tender plants bringing them into your greenhouse and keeping them frost free will ensure they survive until the following year when you can plant them out again. It’s easy to keep your greenhouse frost free by insulating your greenhouse, using garden fleece to cover your plants or by adding a heater and using its frost stat setting to ensure your greenhouse remains frost free. 

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