How Much Does A Greenhouse Heater Cost To Run?

How much does a greenhouse heater cost to run will be affected by a number of factors, including the following:

• The size of your greenhouse
• The temperature you want to maintain inside your greenhouse
• What type of heater you can use in your greenhouse

How Much Does A Greenhouse Heater Cost To Run? - The Size Of Your Greenhouse 

Depending on whether you want to heat your whole greenhouse or just part of it, the size of your greenhouse is incredibly important . . . as we all know it costs more to heat a large area compared to a small area.

We usually think of greenhouse size in feet . . . so you might say that you have a 6ft by 8ft greenhouse . . . this is the traditional way to think of greenhouse size in the UK, rather than talking about the size in metres. So in this post we will continue our conversation in these traditional greenhouse sizes.

As well as the width and length of your greenhouse, what you also need to consider is the height of the greenhouse – as this will also affect the overall area space you will need to heat.  With most gardeners recommending an eaves height of around 5ft as this will provide sufficient height to accommodate staging / benching which you can work at and at the same time allow maximum light into your greenhouse.

So, with the width, length and height of your greenhouse known, you could calculate the square footage you need to heat and use an online calculator to work out what size / strength / power of heater you need to heat the area.

But to make it as quick and easy for you as possible, at Two Wests we have put together a table of recommended greenhouse heater wattage you could use to keep a traditional apex shaped, free standing greenhouse frost free (approx. 40 degree Fahrenheit / 4.5 degrees Celsius).

Using the table above you should now be able to choose a heater suitable for keeping your greenhouse frost free – remembering that you should look at the wattage the heater will provide and choose one closest to your requirement.

Again, we’ve made this simple, by creating a table for you showing the heaters which would be suitable. For simplicity we have assumed that you are going to insulate your greenhouse prior to using a heater to be as economical as possible.

You will see with the table above that the same heater can be used in lots of different sized greenhouses – it’s economical to do this as they are all thermostatically controlled and some feature multiple power settings.

We haven't mentioned the paraffin heaters as the most powerful one we stock has a 600 watt output, so not really providing sufficient heat for these sizes of greenhouse unless used in multiples. 

How Much Does A Greenhouse Heater Cost To Run? - The Temperature You Want To Maintain

Looking at the heaters above, we looked at just providing frost protection. However, depending on what you ae growing in your greenhouse over the colder months, you may wish to create a warmer environment for your plants. To do this we have a formulae which will enable you to calculate the power of heater you will need in order to achieve a certain temperature:

First a table to help you . . .

Using the table above, find your greenhouse and it’s surface area and multiply by 0.39.

For example, for a 6ft x 8ft greenhouse the surface area is 200 sq. ft. 200 x 0.39 = 78

Multiple this figure by the number of degrees in Fahrenheit above 25 degrees.

For example, if you require 45 degrees Fahrenheit, multiply it by 20.
78 x 20 = 1560

This is the wattage of heater you would require. However, you can be more economical and insulate your greenhouse and reduce the power of the heater you require. Adding insulation to your greenhouse will reduce the wattage requirements. So if your greenhouse is insulated you can multiply the wattage you calculated by 0.8.

For example, 1560 x 0.8 = 1248 watts.

How Much Does A Greenhouse Heater Cost To Run? - The Type Of Heater You Can Use

So far, we have helped you to calculate the wattage of heater you need to either provide frost protection throughout your greenhouse or a higher temperature. But we have assumed that you can use any type of heater – be it electric, gas or paraffin. But we are often restricted in the type of heater we can use depending on the location of the greenhouse and what sources of power you have available. So here we take a look at your choices and their associated costs:

Electric Greenhouse Heaters

If you have access to electricity in your greenhouse, then an electric heater would be your best choice as they are the easiest heaters to install and operate. Electric fan heaters are also good as they circulate the warmer air around the whole of your greenhouse quickly and evenly - and many fan heaters also have the option of being set on a fan only setting so can be used in the summer to circulate the air.

So it then just comes out to working out the cost of running your electric heater.

To calculate the cost of running an electric heater in your greenhouse, you need to know the wattage of your heater and how much you pay per KW for electricity – this should be shown on your electricity bill.

Research online (October 2023) has shown us that due to the Energy Price Guarantee, the price of electricity is currently approx. 34p per kWh (a kilowatt hour – how much energy you are using per hour). So it’s then a simple calculation to see what the maximum cost could be, for example:

Using a 2KW heater, if on constantly, 24 hours a day
2 x 0.34 = 68p per hour 24 x 0.68 = £16.32 per day.

This might sound expensive, but what you need to consider is would your heater be running on full power all day? It’s unlikely as your heater will be thermostatically controlled and will automatically turn on and off to maintain the temperature you have set.

So, depending on the temperature outdoors, will affect what the temperature would be inside your greenhouse without heat and what it would cost to lift the temperature to suit what you are growing.

If you want to make a good, educated guess prior to purchasing an electric heater we would recommend using a max/min thermometer in your greenhouse to monitor the temperature for a minimum of 7 days and based on these readings you should be able to calculate if your heater would have to be on every day, whether it would just be on overnight, etc etc.

Gas Greenhouse Heaters

If you haven't got access to electricity in your greenhouse, then the next most popular heater to use to keep your greenhouse warm is one powered by propane gas.

Propane gas is sold in large bottle - we recommend you use a 19kg gas cylinder or larger - so you need space to situate both your heater and the gas bottle. Unlike electric heaters where power is usually available 24/7, with a propane gas heater you do need to make note of how much gas you have left so you don't run out. Plus, with gas heaters it's all about safety and having the heater installed in the correct way and monitored over their life to make sure parts don't deteriorate. You can read more on this aspect by clicking here. 

When looking to purchase a 19kg bottle of propane gas (October 2023) prices online range from £36.95 up to £124.99, with the average price being approx. £50.

To then work out how much it would cost to use a propane gas heater we consulted with one of our greenhouse gas heater suppliers and here is the calculation to use:

For 1KW of heat you would use 0.074kg of gas per hour.
So for a 3KW heater you would use (3 x 0.074kg) 0.222kg/hr of propane gas.

Assuming that your heater was on high, for 8 hours a day, you would use 1.776kg/day.

Based on this a 19kg bottle would last 10.6 days. At a cost on average of £50 for a 19kg gas bottle, price per day running for 8 hours would be £4.72. If run 24 hours a day cost would be approx. £13.88 per day.

(This formula assumes a standard propane gas at 37 mBar).

Paraffin Greenhouse Heaters

We would only recommend a paraffin heater for your greenhouse when you have no other option – so when you haven’t got access to electricity or natural gas and don’t have space for bottled propane gas.

Researching current prices (October 2023) for paraffin to fuel these heaters the average cost is approx. £12.99 for 4 litres. This will help you to calculate the cost of using a paraffin heater when you look at the capacity of the heaters and from full how many days of burning you would get:

Based on this, if you take the mini paraffin heater, this size paraffin heater will use approx. 1.4 litres of paraffin per day. If you were to be on all day, it would cost approx. £4.55 in paraffin. However, it is unlikely that you would have it running 24/7, so you can start to reduce the cost based on the number of hours it would be operating. 

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!