How Much Electricity Does A Greenhouse Heater Use?

We are often asked ‘How much will it cost to run my greenhouse heater?’ and it’s a tricky question to answer just because there are so many variables which affect greenhouse heater use. Some of the main factors include:

• The power of the heater – in this post we are concentrating on electric greenhouse heaters – with the ‘power’ of the heater being shown as watts or kilowatts.
• The temperature you want to maintain – if you are only using your greenhouse to overwinter plants which need to be kept frost free this will require less heat than if you are wanting to maintain tropical conditions.
• The outside temperature – the lower the temperature outside your greenhouse, the harder your heater will have to work to lift the temperature in your greenhouse, so the heater will be on for longer or using more power.
• The state of your greenhouse – if you keep your greenhouse well maintained, with no cracked glazing, correctly fitting roof vents and doors, insulated throughout the colder months, then more heat will be kept inside the greenhouse rather than lost through gaps, so your heater shouldn’t need to be on as long.
• The price of your electricity – the simplest way to check what you pay for your electricity is to check your bill and there should be a price per KW. You can use this to help calculate the maximum cost of running an electric greenhouse heater.

Let’s take a look into each of these factors in more detail to help you understand the cost of using an electric greenhouse heater and also to give you some helpful advice to ensure you are using it efficiently.

How Much Electricity Does A Greenhouse Heater Use? - The Power Of The Heater 

When it comes to electric greenhouse heaters there are lots of options available to you, enabling you to choose the most appropriate one for your needs. The power or strength of the heater will be shown in either watts or kilowatts, which relates to how much electricity it would use in an hour when being used, with the lower the wattage the lower the amount of electricity used and the less it will cost to run.

A good example is when you compare electric tubular heaters to electric fan heaters.

Electric tubular heaters are seen as being a cost-effective way to lift the temperature as they are low wattage, from as little as 28 watts per foot length.

Slimline Eco Heaters Starting at just 1ft long, these tubular heaters are safe to use in a greenhouse environment as they have an IP44 weatherproof rating. A beneficial feature of these tubular heaters is that they incorporate a built-in thermostat, enabling the heater to be automatically turned off and on to maintain a required temperature in your greenhouse. Click here for full details of these heaters.

Although cost effective to run due to their low wattage, they are designed for low-level, background heating so are perfect for preventing condensation, freezing and damp in small spaces but are not suitable for using to heat a greenhouse for propagation. For larger greenhouses or higher temperatures you would need to purchase multiple tubular heaters and it would probably be wiser in this case to invest in an electric fan heater.

Electric fan heaters which are suitable for use in greenhouse environments come in a wide range of sizes, shapes, and wattages, so it is important to choose the appropriate one to suit the space it is being used in. The larger the area to be heated, the more powerful the heater needs to be, and this may also affect the physical dimensions of the heater, as the more powerful heaters will need stronger, potentially larger fans, to circulate the warm air.

So whilst selecting the correct wattage of heater, you also need to consider where it will be stood during operation, so that you know you have space to accommodate it. To help with this, you will find that many of the larger electric fan heaters have been designed to either be stood on a solid surface or supplied with chains to be hung from the greenhouse roof. Those which can be hung neatly out of the way are ideal for busy greenhouses where space is at a premium. Our best-selling greenhouse heater, the Bio Green Phoenix, is one of these versatile fan heaters.

Bio Green Phoenix
This is a powerful 2.8KW fan heater making it ideal for heating greenhouses up to 10ft x 12ft.

For maximum flexibility when siting this heater in your greenhouse it is supplied with both foot brackets to enable it to be used free-standing and chains to allow it to be hung from the roof of your greenhouse.

If you want to use this heater in smaller greenhouses this has been made easy and efficient by the heater featuring three heat output settings – 1KW, 1.8KW or 2.8KW – and it can be used all year around as you could use it on the fan only setting during the summer months to help circulate the air.

Click here for full details of this greenhouse heater.

Once you have decided on which heater would be suitable for your greenhouse size, then you can calculate the maximum it would cost to run per hour or per day by comparing the wattage of the heater and the cost you pay per KW for your electricity.

To help you with the running costs we have created a simple table below which shows you the power of the electric heater and the cost to run per 24 hours if running on full power, with an electricity cost of 34p per kWh (the current Energy Price Guarantee in October 2023). 

Just remember, the costs above are the maximum if your heater was on continuously for 24 hours. In reality, if your heater incorporates a thermostat, then the heater will automatically turn off and on to maintain a set temperature, so should not be constantly running unless you are trying to maintain a high temperature or outside temperatures are extremely cold.

How Much Electricity Does A Greenhouse Heater Use? - The Temperature You Want To Maintain

If you are lucky enough to have a greenhouse, then you are likely to want to be able to use it all year round. Under ideal conditions, you would be able to use your greenhouse to raise crops or flowers regardless of the season, but in reality, within the UK, our weather fluctuates so much throughout the year that in order to use our greenhouse in the cold months as well as of the hotter months, will require some form of heating. And heating a greenhouse will come at a cost.

In the table above we have helped you to see the potential costs of using an electric heater in your greenhouse, here we will help you to decide what temperature you will want to maintain in your greenhouse in the colder months – this will affect how long your heater will need to be on and as a result, the costs involved.

Most domestic greenhouses are used by amateur gardeners to enable them to raise greenhouse crops, such as tomatoes (research has shown that approx. 90% of all greenhouses are used for tomato growing) or to raise annuals. Whilst specialist growers might be using their greenhouses to raise alpines or cacti or orchids for example. In fact there are simply so many plants which can be grown within a greenhouse that the range of temperatures required will vary greatly. If you are a specialist grower, you are likely to be very familiar with the temperature required to keep your plants healthy and thriving. If you are a new gardener with your first greenhouse or simply trying to raise a new vegetable crop or flowering plant, then you are likely to need assistance.

If you are growing from seed, then the most valuable place to look for guidance on growing temperatures is the seed packet. Usually the seed packet will give you details on when to sow the seeds and the germination temperature required so use this as your guide. Or look online to see the recommended growing temperature for the plants you are raising.

When you only want to use your greenhouse in the colder months to over winter more tender plants, then you might only need to keep your greenhouse frost free. When this is the case, the costs involved in keeping your greenhouse frost free will be much less than if you were growing tropical plants. So moving more tender plants into your greenhouse through the colder months could be more cost effective than if you had to replace those plants damaged by frost through the winter.

How Much Electricity Does A Greenhouse Heater Use? - The Outside Temperature

If you do only need to keep your greenhouse frost free, then before investing in a heater you need to first check what the temperature is in the greenhouse compared to the outside temperature. To do this ideally you need a max min thermometer which will enable you to check the highest and lowest temperatures. In an ideal world you would use two thermometers – one inside your greenhouse and one outside. Monitoring this way should show that even in an uninsulated greenhouse, your inside greenhouse temperature should be 2-3 degrees Celsius higher than the outside temperature.

Remember, when measuring temperatures outdoors, you need to use a thermometer which is weatherproof / waterproof so it can be left outdoors without damage – check this before ordering your thermometer.

We always recommend insulating your greenhouse prior to using a greenhouse heater as this will help to reduce your heating costs by helping to keep the heart generated within the greenhouse. However, you could find that simply insulating your greenhouse could lift the temperature in your greenhouse 5-6 degrees Celsius higher than the outside temperature – and when you want to just keep your greenhouse frost free this could be sufficient.

So, if you have time, and plan ahead, install your insulation and monitor the temperature for a week to see if you do get this lift in temperature compared to the outside temperature.

If you would like to read more about frost protection click here to read our A to Z Guide To Frost. 

How Much Electricity Does A Greenhouse Heater Use? - The State Of Your Greenhouse

As canny gardeners we won’t want to waste money, so before using a heater in your greenhouse you need to check that it is in a good state of repair – what you don’t want to do is add a heater and then the warm air generated simply escapes out of the greenhouse! So, before fixing insulation in your greenhouse and adding a heater, give it a quick maintenance check to make sure everything is in working order pre the colder months.

Clean your greenhouse glazing and frame, at the same time checking that the glazing is being held securely in place and that there is no damage.

When you add insulation to your greenhouse this will reduce the light able to entre your greenhouse, so you need to give it a thorough clean so as much light as possible can enter. You should clean both the inside and outside of your greenhouse panes, removing any leaves from the top of your greenhouse as you clean. For glass or polycarbonate glazing simply soapy water and a soft sponge, cloth or soft bristled brush should be sufficient. Be mindful of using chemical cleaning sprays as these could damage the glazing, the frame and potentially harm any plants. If you do want or need to use a disinfectant use something like Citrox which is based on natural ingredients and will clean efficiently without causing any harm.

If you find any of the glazing is cracked, you could seal the cracks using all weather tape or a sealant. Where the glazing is broken to an extent that this type of repair would not work then you should replace the broken or damaged pane.

In addition to the frame and glazing, make sure that any moving parts of your greenhouse are working correctly – so that’s a case of checking greenhouse doors, roof vents and louvre windows. Make sure they are opening and closing smoothly, using WD-40 or a silicone-based product where needed. Replace any damaged draught excluder around the door and check it securely closes to help keep the cold air out.

Cleaning & Maintenance Kit If you are planning a day cleaning and repairing your greenhouse, have a kit of spares like this one on hand. It includes replacing glazing clips, nuts and bolts and even a bottle of Citrox, so is a great kit to help you get started.  Click here for full details of this kit.

How Much Electricity Does A Greenhouse Heater Use? - The Price Of Your Electricity

The price you pay for your electricity will depend on your supplier, where you live, the meter type, what tariff you are on and how you pay. So you need to check your electricity bill to see how much you are being charged per kWh.

kWh – this is a kilowatt hour and is what you would pay if you used 1 kW of power in an hour.

Then, depending on the power of the heater – or in fact any electrical item – you can work out how much you would pay to use it per day, per month, per year . . . This means a simple formula makes it easy to work out potential costs:

The formula needs you to know the kW of your electrical item and the kWh that you pay. For example, you can work out how much you spend to run your fridge.

If your wattage of your fridge is 350 watts and you pay 34p per kWh, what you would pay:
0.35 x 0.34 = 0.119 per hour to run
0.119 x 24 = £2.86 per day
1.19 x 7 = £20.02 per week
20.02 x 52 = £1041.04 per year

Therefore If your greenhouse heater is 2kW, your calculation would be:
2 x 0.34 = 0.68 per hour to run
0.68 x 24 = £16.32 per day
16.32 x 7 = £114.24 per week

What you should also remember when using a heater in your greenhouse, using an electric greenhouse heater is by far the simplest method.

Electric heaters are easy and safe to use, very often they will incorporate a thermostat which will help you to maintain a required temperature, by automatically turning the heater off and on to keep an even temperature. Many electric greenhouse heaters also use a fan to ensure quick, even distribution of the warmer air throughout the whole greenhouse space. Circulating the air throughout your greenhouse also helps to maintain a healthy growing environment, helping to prevent many fungal and bacterial diseases from taking hold due to stagnant air. This type of heat also doesn’t produce any negative side effects – an electric heater will not increase the air humidity, will not produce any odours, or add anything into the air which requires ventilation for it to be extracted to maintain a healthy growing environment. And you should never run out of fuel – unlike propane gas heaters and paraffin heaters where you must ensure that you have fuel available to keep the heaters operating, with an electric heater as long as there isn’t a power cut there should be nothing to worry about.

So, although the cost of running an electric heater may work out more than if you were to use a gas or paraffin heater, the fact of how easy an electric greenhouse heater is to use may well still make if the best choice. 

Our blog posts are created from our personal knowledge, information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human. if you have any queries you can contact us today!