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Heat Pumps Explained

Heat pump mounted on external wall

With gas boilers looking to be a thing of the past in new builds, what exactly will replace them? 

In a recent Twitter poll, we asked our followers – many of whom are tradespeople – what they believe will replace gas boilers. The majority of the votes went to heat pumps.

Heat pumps have been around for some time but are increasing in popularity. They work by transferring heat from a source to your home. The heat extracted warms your home using a compressor and a circulating liquid or gas refrigerant structure.


Though the pump does require electricity to run, it should require less electrical energy than the heat it produces. (Source: Which)

Compared to boilers, heat pumps use less electricity and achieve an efficiency rate of 200-600%. (GreenMatch), making them an ideal alternative to gas boilers. However, while they may work well for new builds, there may be some roadblocks if you want one installed to replace your current heating system.

With several factors to consider including where you live and cost, heat pumps may not be for everyone. And though they may not be replacing your gas boiler soon, they are set to be seen in new-builds across the UK.

There are currently three main types of heat pumps, and it is vital to know how each work to find out which is suitable for your home or development.

Ground Source Heat PumpsHeat Pumps in workshop

The earth is continuously soaking up and retaining heat from the sun. Ground source heat pumps work by extracting that heat from the land and using it inside your home. Turning heat into a hot water supply, GSHPs turn a large amount of warm water into a small amount of hot water.

As temperatures in the UK stay consistently around 11 degrees Celsius, you can use a heat pump throughout the year. However, as they operate at lower temperatures than your usual gas heating system, underfloor heating and low surface temperature radiators are recommended for maximum efficiency.

There are currently two different ground source heat pumps; closed-loop and open-loop.

A closed-loop system draws heat from the ground itself. The piping loops contain a liquid similar to anti-freeze that transfers the temperature to the heat pump. Engineers can install closed-loop systems either horizontally or vertically. 

Horizontal systems are buried 1-2 meters underground and best suited to homes built on a large amount of land. However, vertical designs are an option if a house lacks the land required for a traditional approach. 

A 6m hole is dug to install insulation and piping. Depending on your home’s size and requirements, piping can range from 50m to 150m.

An open-loop system extracts groundwater as it passes through the heat pump. This style of GSHP is less common due to the requirement of an ample water supply such as a well or pond. The water is pumped into the heat pump and used for heating before being disposed of.

The water is pumped back to the water source or disposed of via surface drainage.

Air Source Heat Pump

Another option is an air source heat pump. More affordable than ground source heat pumps, they are also easier to install.

Air Source Heat Pumps work by absorbing heat from the air at a low temperature and turning it into a fluid. (Source: EnergySavingTrust) The fluid passes through a compressor, increases the temperature, and transfers heat to the house’s heating and hot water circuits.  

With two versions of the ASHP, you can choose between an air-to-water system or an air-to-air system depending on the type of heat distribution you require.

Air-to-air heat pumps absorb heat from outside and transfer it into your home via a fan.

Air-to-water heat pumps absorb heat from outside but transfer it through your heating system, including radiators, underfloor heating and hot water.

ASHP’s differ from gas and oil boilers as they need to be on continuously throughout the colder months efficiently to heat your home. Rather than the high temperatures delivered by traditional heating systems, ASHPs are cooler but keep your home at a comfortable temperature. When considering installing an ASHP, it is worthwhile exploring how to insulate your home best to get the most out of them. Generally, they work best with larger radiators and underfloor heating.

Fitted outside your home, ASHP’s are usually installed on a wall or the ground. Ideally, somewhere with plenty of space and sunlight is best, with little noise disturbance.

If for whatever reason, your home fails to meet all the criteria for a heat pump, you can instead opt for a hybrid version that works in conjunction with a gas or oil boiler.

Water Source Heat Pump

Using lakes, ponds, rivers, or springs, you can heat your home with a water source heat pump. Like ASHPs and GSHPs, a water source heat pump uses a refrigerant to transfer heat to your home.

In the same way as GSHPs, water pumps are laid in a closed-loop or open-loop system. In a closed-loop system, water and anti-freeze combine in a series of panels and coils within the water source. The system absorbs energy from the water, which is then delivered to the heat pump as it moves through the coils. In the open-loop system, water is pumped to a heat pump and back again from the water source.

CostTwo stacks on coins

Initially, heat pumps are not the most affordable way to heat your home, but if they turn out to be the most eco-friendly, they may be the best option for the sake of the environment. They also have several long term benefits, including the amount of money saved over time.

Compared to traditional heating systems’ running costs, heat pumps are more affordable. Saving money each month, you may also get support from the government through their sustainable solutions. For example, the Renewable Heat Incentive (RHI) will pay you for each unit of energy you generate for a total of 7 years.

Though your property may determine the kind of heat pump you can install, it may well be the cost that impacts your decision if you meet the criteria for all.

In October 2021, the UK government announced a £450 million investment to help fund heat pump installation throughout England and Wales. A grant of up to £5,000 is available, meaning approximately 90,000 homes will benefit from the scheme if they receive the total grant amount.

So, how far will £5,000 go to help cover heat pump installation costs?

Installation can vary drastically between £8,000 to £45,000, and the running cost can vary depending on the insulation quality and size of your home. The most affordable of the three is an air source heat pump, ranging from £8,000-£18,000. ASHP’s are likely to be the more popular choice due to cost and the lack of land requirement. Water source heat pumps are the middle option with prices starting at £20,000 and going up to £32,000. Finally, a ground source heat pump may set you back anywhere from £20,000 to £45,000.


  • Renewable Heat Incentive: You can receive payments for each kWh of energy your heat pump generates.
  • Low Running Cost – Homeowners can save up to £1350 each year compared to traditional heating systems.
  • Low Maintenance – A heat pump inspection is only needed every 3-5 years.
  • Long Lifespan: Though they can last up to 50 years, a heat pump’s average lifespan is 14-15 years.
  • Environmentally Friendly – They do not require fossil fuels to run.
  • Keep Cool – As well as keeping you warm in the colder months, heat pumps can cool your home in the warmer months.


  • High upfront cost – Costs can be anywhere between £8,000 – £45,000 to install a heat pump in your home.
  • Difficult to install – Though not the case all the time, some kinds can be challenging to install, e.g. GSHP’s need suitable geology.
  • Specific Requirements – You would have to install underfloor heating and large radiators for heat pumps to run at their most efficient.
  • Planning Permission – You may need planning permission in Wales and Northern Ireland. In England and Scotland, it depends on the location and size of the property.
  • Extreme Temperatures – Extreme cold weather can cause damage to the system.
  • Eco Concerns – There are some environmental concerns regarding the fluid used in the pipe system.
  • Insulation – If you live in low energy-efficient or draft-prone property, installing a heat pump without other energy-efficient measures could result in the pump not reaching its full potential.
All data correct at time of publication.