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ABC Guide to Greenhouse Heaters

Written on 16/10/2015 at 15:35

At we want to make sure that you select the correct greenhouse heater for your requirements, that's why we have come up with this simple ABC guide to greenhouse heaters. By following these simple steps you can select the correct heater for your Greenhouse.

A - Selecting a Fuel Type

There are 4 main fuel types for running a greenhouse heater. Select your fuel type based on the following main advantages and drawbacks:-

Tomatoes in greenhouse Electric Heaters

There are a number of advantages with electric heaters such as the lack of fumes, thermostatic control and that most electric heaters are fan assisted.

The main advantage is that when you set up an electric greenhouse heater you can just leave it without having to worry about refuelling as you would with propane or paraffin.

Also, having a heater with a fan means you get a better distribution of heat, therefore your plants furthest away from the heater will have better protection as the warm air is pushed around the greenhouse. Without a fan there will be a much greater variance of heat around the greenhouse, especially in the corners furthest away from the heat source. You will also find that the heat distribution will be slightly better from a heater that is hung from the roof as opposed to a floor standing unit.

Many electric heaters can also be used in the summer as they often double up as a cold air fan to allow air circulation around the greenhouse. Air circulation helps keep a uniform temperature and humidity throughout the greenhouse.

An electric greenhouse heater is only going to be an option if you have an existing source of electricity in your greenhouse or you have a safe way of getting a supply that will comply with UK regulations. We recommend that any supply is set up by a qualified electrician that is up to date on the current regulations. It is likely that a new supply to a greenhouse would be installed using armoured cables buried underground.

Propane Heaters
If it's not possible to get electricity to a greenhouse, propane is usually the second choice for medium to large greenhouses. Although they are not as efficient and they produce fumes from the burning process, they are an easy solution to get heat into the greenhouse. It's fairly easy to get hold of a propane bottle in the UK, but it will need to be stored safely.

Natural Gas Heaters
Having a gas supply in your greenhouse takes the need away from obtaining a propane bottle and replacing the bottle periodically, but the initial outlay of getting a gas supply to your greenhouse makes this the least popular choice.

Paraffin Heaters
This is usually only an option for smaller greenhouses and cold frames. A paraffin heater will need to be refilled frequently and the wick will also need maintenance. The heat control will be very basic and we would only recommend using a paraffin heater for frost protection or as backup for a main heater. If not used and maintained correctly, a paraffin heater can produce black smoke which coats the inside of the greenhouse. This is usually down to the wick being too high or not trimmed correctly.

B - Measuring Your Greenhouse

The size of your greenhouse is extremely important when selecting a greenhouse heater. We have categorised our heaters into four groups to make selection easier.

>> Cold Frame / Mini Greenhouse up to (6ft by 6ft)
>> Small Greenhouses under (6ft by 8ft)
>> Medium Greenhouse up to (10ft by 12ft)
>> Large Greenhouse over (10ft by 12ft)

Although it's possible to view the heaters suitable for your greenhouse in these groupings, we suggest that you read step C first as the heating requirements will impact the Kw rating required.

We have kept our calculations simple by only referring to the square foot floor area of the greenhouse and not the volume of the greenhouse. There are many other variables that could be taken into account when choosing a heater so unless you are also going to make adjustments for dwarf walls, harsh winds in exposed areas, protection provided by the position of the house, then it's probably not worth worrying about the height of the greenhouse unless it is particularly tall.

You can always apply some common sense adjustments if required but it's better to get an overpowered heater that can be adjusted down rather than one that isn't up to the job.

Greenhouse in Winter

C - Your Heating Requirements

Your greenhouse sizes isn't the only factor to consider when selecting the power output of the heater. You need to consider your heating requirements. Are you trying to heat your greenhouse or just offer frost protection?

The following guide allows you to work out the kw output needed to provide the required heat levels in your greenhouse. It doesn't need to be exact as the heaters are adjustable.

1Kw - Heat 48sq ft - Frost Protection 80sq ft
2Kw - Heat 60sq ft - Frost Protection 120sq ft
3Kw - Heat 120sq ft - Frost Protection 260sq ft
4Kw - Heat 150sq ft - Frost Protection 350sq ft
6Kw - Heat 200sq ft - Frost Protection 500sq ft

Beware of fuel estimate calculators on the internet, we have found that they are not at all accurate. The purpose of these are to estimate the amount of fuel you will use during the winter but we have tested these out and they appear to be very inaccurate. We have even managed to come out with negative values, meaning that if you use a greenhouse heater then according to the calculators you would actually be getting a cheque back from the power companies.

The reason these will not work is that many people use a greenhouse heater to protect from frost and in effect they will only turn on when the outside temperature drops below the required temperature, so no matter what the average temperature during the winter you are only actually using the heater at certain times and the lower the outside temperature the harder the heater has to work and the more fuel it will use.

If you now know which fuel type you need and the required kw output you can make your purchase.

View by Fuel Type
>> Electric Heaters
>> Propane Heaters
>> Paraffin Heaters
>> Natural Gas Heaters

View by KW Range
>> 0 to 1Kw
>> 1Kw to 2.25Kw
>> 1.5Kw to 3Kw
>> 3Kw and Over

Greenhouse Insulation

Don't forget to consider insulating your greenhouse. It doesn't matter which heater you buy, you will always benefit from insulating the greenhouse. You will find that on the coldest nights your heater will be more likely to cope with severe weather if it is insulated. It will also help stop your fuel bill from racking up whilst the heater is working it's hardest to protect your plants from the outside elements.

The first stage of insulation and saving money would be to replace any broken panes and ensure that the vents and doors are tight and sealed as best as possible. After that the best form of insulation would be bubble polythene and it's worth considering partitioning the greenhouse if you can move the plants into one area. The partition need not be permanent. You could hang bubble from the ceiling and create a wall of bubble insulation. Please ensure that your heat source is placed a sufficient distance from the insulation to avoid risk of fire.

Fleece could be used to protect the plants by draping it over them or by using fleece bags, some have draw string, that cover larger plants.

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