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Heat pumps

Posted by PFP Energy

As we move towards net zero, we need to be thinking about the way we heat our homes. Today, boilers are the most common central heating devices, but these gas guzzling monsters aren’t the least bit green. Current efforts to solve this issue include using green gas, which is currently uncommon, and offsetting carbon emissions – a solution that will only work in the short term. Enter – the heat pump.

What are heat pumps?

There are three types of heat pump – air source, water source and ground source. The source type (air/ground/water) tells you where they take their energy from. Each works using a slightly different mechanism, and each has its own appeal. Since air and ground source heat pumps are the most common and accessible, our focus will be on them.

How heat pumps work

During the process of heating your home, heat pumps work by taking thermal energy from outside and moving it into your home. Plainly, they make one place colder to make another place hotter (the same process as a fridge but with the goal of heating rather than cooling). Heat pumps operate in a four-step cycle. The air and ground source heat pump cycles are almost identical, so here is the air source cycle as an example (pictured):

  1. A fan draws in air from outside.
  2. A heat exchanger transfers heat from the air to a fluid called refrigerant.
  3. The heat evaporates the refrigerant. The gaseous refrigerant passes through a compressor to increase its temperature.
  4. A second heat exchanger transfers heat in the refrigerant to the home.

The only difference between air source and ground source heat pumps is in step 1. Ground source heat pumps use buried pipes (ground loops). In this case, it is the heat from the fluid in these buried pipes that is transferred into the refrigerant rather than the heat from the air.

Diagram of how heat pumps generate energy

Which heat pump is right for you?

Air source heat pumps tend to cost between £6,000 and £8,000, depending on brand and heat output, whereas ground source heat pumps typically cost £10,000 to £18,000. This additional cost is mainly due to the digging involved in installation of the ground loop – the part of the heat pump that takes the heat from the ground. Although they’re more expensive, ground source heat pumps are also more efficient than other types and you get a larger Renewable Heat Incentive (RHI) grant for them. In other words, you save more money whilst helping to save the planet. However, they require lots of space outdoors, whereas air source heat pumps only need a small space of approximately one square meter on the side of your house.

The problem with boilers

Most UK households use boilers to heat the house and water. Boilers use natural gas, which releases greenhouse gases when burnt. Because heating requires so much energy, this makes up a significant proportion of domestic emissions. The difficulty is that renewable (green) gas is a lot harder to come by than renewable (green) electricity so using sustainably sourced gas seems a long way in the future. Luckily, there are a few other alternatives to a gas boiler:

  • Buy a heat pump – Heat pumps are much more efficient than boilers and so consume far less energy which is great for the planet and your pocket. The energy they do consume is also electrical which, depending on your supplier, can be renewable. If you haven’t already, you can sign up with us today to get 100% green electricity. Heat pumps can be used in conjunction with a boiler and in many cases can even fully replace one. Other advantages of heat pumps over boilers include less maintenance and longer life span. It can even be reversed to act as a cooling air conditioner on hot summer days.


  • Go electric – You can go electric by exchanging water filled radiators with electric ones, buying an electric immersion heater and, whilst you’re at it, switch your gas hobs and oven for electric. These changes can be made environmentally friendly by choosing a renewable electricity tariff to power them. Bear in mind though that whilst the upfront cost of appliance changes may be less than that of a heat pump, a heat pump is much more efficient meaning it will be cheaper in the long run.


  • Carbon offset your gas – This will make your net emissions zero by paying for carbon reduction/removal projects around the globe. Offsetting has the advantage of giving you the power to make a difference globally, but it is not a long-term solution; eventually, the gas problem must be confronted either by using green gas or going electric.

The problem with heat pumps

Besides the obvious upfront cost, heat pumps only have two notable shortcomings compared to boilers:

  • They have a low output temperature so you may need to improve your insulation if you are thinking about getting one for central heating. Similarly, you will likely need a bigger hot water tank for heating water. Your house will heat up slower than using a boiler, but you will be able to get to the temperature you want eventually if your insulation is good enough.


  • At extreme low temperatures heat pumps do not work as effectively and may struggle to meet your heating needs on their own. As a result, heat pumps often come with a supplemental electric heater for those super chilly days.

Key terms

Renewable Heat Incentive (RHI) – a government financial incentive to promote the use of renewable heat. You are not eligible for this if you use a water source heat pump.

Greenhouse gas – gases in the atmosphere that trap heat and cause global warming.

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