How the Heat Pumps Work

How the Heat Pumps Work

A heat pump is a device that takes heat from the outside and transfers it into your home. It does so by using energy, but the amount of heat given to your home exceeds the amount of electricity necessary to operate the system. A heat pump does not emit carbon dioxide since it collects heat that is already present in the environment.

Thermal energy – or heat – is present in everything around us. Heat naturally moves from a warmer to a colder environment. We need heat to move in the opposite way – from a colder place to a warmer place – in order to utilise heat energy in a home when exterior temperatures are colder. But how does it accomplish this?

The temperature of fluid rises as the pressure of the fluid rises. When the pressure drops, so does the temperature. So the key to how a heat pump works is the link between pressure and temperature.

A refrigerant is a term used to describe fluid. The heat pump compresses the fluid with electricity, raising the pressure and thus the temperature.  As the heat from the fluid is transported to your home, it cools slightly. After that, the fluid is allowed to expand and chill even further. It’s now cold enough outside to absorb more heat and restart the process. The heat can then be used in your home’s central heating system (in an air-to-water or ground-to-water heat pump), or it can be passed through hot air blowers (in an air-to-air heat pump).

Types of Heat Pumps

Air Source Heat Pumps

An air-source heat pump is a popular option for heating your home. You’ll be able to generate your own renewable heat and maybe save money on your energy costs as a result. They produce heat at a lower temperature than gas or oil boilers. As a result, in order to heat your home to a reasonable temperature, you’ll have to run them for significantly longer periods of time. If you’re replacing a costly system then keep in mind that a well-insulated home is vital. Otherwise, the heat generated by the pump will escape more easily.

Heating your home with an air source heat pump is a low-carbon option. They collect heat from a cooler environment and transfer it to your home, raising the temperature. Air source heat pumps resemble air conditioners in appearance. The size of your heat pump is determined by how much heat it will need to generate for your home; the larger the heat pump, the more heat it will generate. Air source heat pumps are classified as either air-to-water or air-to-air. They operate in a variety of ways and are compatible with a variety of heating systems.

How Does it Operate?

An air-source heat pump uses a compressor to extract heat from the air and boost it to a higher temperature. The heat is subsequently transferred to your home’s heating system. They work in a similar way to reverse refrigerators.

  1. The air source heat pump collects heat from the outside air and transfers it to a low-temperature liquid refrigerant.
  2. The pump compresses the liquid using electricity to raise its temperature. It then condenses back into a liquid, releasing the heat it has accumulated.
  3. Your radiators or underfloor heaters receive heat. You can keep the rest in your hot water cylinder.
  4. You can enjoy your showers and baths with running hot water taps from the hot water you’ve stored.

Advantages and Disadvantages

Air source heat pumps are low-maintenance systems that can offer both heating and hot water, but they aren’t perfect.


  • Air source heat pumps use less energy and produce less CO2 than many other heating systems.
  • Installing an air source heat pump is less disruptive than ground source heat pump, especially if you’re retrofitting.
  • Renewable Heat Incentive payments are available for air-to-water heat pumps.
  • When compared to outdated systems, you may be able to save money on heating.


  • For the exterior condenser unit, you’ll need ample space in your house.
  • Condenser units can be noisy, as they blow colder air into the close vicinity.
  • Because electricity is required to operate the pump, they are not carbon-neutral (unless the electricity comes from a renewable source such as solar panels or a wind turbine).

Ground Source Heat Pumps

By pumping water through pipes, a ground source heat pump system extracts natural heat from the ground. The heat pump then raises the temperature, which is then used to heat the residence or deliver hot water. They require electricity to operate, but the concept is that they consume less electricity than they generate in terms of heat. In a central heating system, the pump serves in the same capacity as a boiler. However, instead of burning fuel to generate heat, it harnesses ambient heat from the ground. 

How Does it Operate?

A ground loop (a network of underground water pipes) plus a heat pump at ground level make up ground source heat pump systems. A solution of water and antifreeze is pumped around the ground loop, absorbing the heat stored naturally in the earth. The compressed water mixture passes via a heat exchanger, which extracts the heat and sends it to the heat pump. Your home’s heating system then receives the heat.

  1. Fluid is used to absorb heat from the ground in a ground source heat pump.
  2. The fluid is compressed and heated to a higher temperature using electricity.
  3. The remaining heat is stored in a hot water cylinder and distributed to radiators or underfloor heating.
  4. Showers, baths, and taps can all use the hot water that has been stored.

Although the hotter you heat your water, the more electricity you’ll consume, a ground source heat pump can raise the temperature from the ground to roughly 50°C. This heat can then be used to heat a radiator, water, or an underfloor heating system. Whether you’ll need a backup heating system depends on the size of your home.

Advantages and Disadvantages


  • Financial assistance is available to help with the cost of a ground source heat pump.
  • The pump that circulates the liquid in the ground loop must be powered by electricity. However, you obtain between two and four units of heat for every unit of power used by the pump, making this a cost-effective approach to heat a structure.
  • There are seven different electricity tariffs that can be employed to reduce the cost of electricity used to run the heat pump.


  • Installing a ground source heat pump is expensive. 
  • If space is limited and a borehole is necessary, the groundworks required to build the trench can be costly and disruptive. Planning approval may be required if space is limited and a borehole is required.
  • They are often incompatible with buildings that already have gas-fired central heating. Because the technology operates at lower temperatures, it’s best for homes with underfloor heating or huge radiators.

The Efficiency of Heat Pumps

Efficiency of Heat Pumps

The effectiveness of a heat pump is determined by the temperature of the ‘source,’ which can be either the air or the earth in this case. The heat pump has to work harder when the source is cooler. This means that while comparing the effectiveness of ground source and air source heat pumps, we must consider the location of the house and the time of year.

For most of the year, air-source heat pumps operate in temperatures ranging from -5°C to 25°C. Of course, there are rare days when it gets much colder, but this temperature range spans at least 95% of the year for most parts of the UK.

Ground source heat pumps absorb heat from the soil, where the temperature is not as hot as it is in the air, but it is not as cold as it is in the air. As long as the ground loops that extract heat from the soil are configured correctly, the soil temperature will stay above five°C for most of the year. This means that the ASHP will be more efficient than the GSHP at certain times of the year, but the ground source heat pump will be more efficient than the air source heat pump when it gets freezing cold.

Aside from being less expensive to build, an ASHP has the advantage of not requiring electricity to pump fluid around pipework outside, as a GSHP does. So, even on days when the air and ground are the same temperatures, an ASHP can be marginally more efficient.GSHPs, on the other hand, are more efficient throughout the course of the year, but the extra cost savings may vary depending on where you live in the country and the weather conditions. The higher you reside in the north, the easier it is to justify the additional cost of a GSHP.

Air source heat pumps may operate at temperatures as low as -15°C, with specific models capable of operating at even lower temperatures. However, if these temperatures occur frequently, you may find that a GSHP or hybrid heat pump is a better choice.

Designing and Operating Your Heat Pump System

Designing and Operating Your Heat Pump System

When the difference in temperature between the outside source temperature and the water temperature needed in your radiators or underfloor heating is larger, the compressor in a heat pump works harder. Conversely, if the heat pump uses less electricity, the lesser the compressor has to run.

While we can’t regulate the temperature of the outdoor source, we can build heating systems that use low-temperature water within, allowing the heat pump to use less electricity while still providing adequate heating.

More heat can be delivered into the area without increasing the water temperature by utilising radiators with a bigger surface area or underfloor heating. Another technique to transfer more heat into the room with lower temperature water is to run the heating system for longer.

The heat pump will have to run at a higher temperature if you have radiators with a lower surface area. This implies the compressor has to work harder to deliver the same quantity of heat as if the radiators were larger or if the compressor had more time to run. When the compressor works harder, it consumes more electricity, increasing the system’s operating costs.

The goal of a well-designed system is to keep the temperature of the heating water as low as feasible. The heat pump will be more efficient and thus have lower operating costs if the needed temperature is near to the source temperature (i.e. outside air or ground temperature).

Installation Costs

According to the Energy Saving Trust (EST), an air-to-water heat pump costs between £9,000 and £11,000. The cost of installing a ground source heat pump varies based on the size of the heat pump, the complexity of the system, and whether you pick simple or complicated controls. 

According to the EST, installing a ground source heat pump cost ranges from £10,000 to £18,000, depending on the size of the system (not including the cost of installing underfloor heating, if necessary).

How do you save money on your heating bills?

How do you save money on your heating bills

While the compressor and pumps require electricity to operate, they consume far less than the amount of heat that is transferred from the outside to the inside. Because the amount of heat energy transported vs the amount of electrical energy utilised is determined by the source and output temperatures. It varies throughout the year as the outside temperatures change.

In the United Kingdom, average heat pump efficiencies range from 3 to 4, with ASHPs on the lower end and GSHPs on the higher end of the scale.

For Longer Life of Your Heat Pump


It’s critical to use your controls correctly if you want to get the best performance out of your heat pump. There are several ways to get the most out of your heat pump, depending on the controls you have and the amount of heating and hot water you require.


A heat pump, like any other heating system, requires regular maintenance to function correctly – fortunately, most heat pumps are simple to maintain and require little input from the end-user. Workmanship guarantees for heat pumps, for example, can last up to ten years with Quality Assured National Warranties (QANW). For a price, many manufacturers also provide warranty extensions. A heat pump can last for 15 years or longer with proper maintenance.

A visual inspection of the water pump, external pipes, fittings, and electronics is typical. Ground source heat pumps may need to be re-pressurised or have the antifreeze quality tested every 2-3 years, which may be done by a professional. Request a documented list of any extra maintenance checks you should perform to ensure everything is working properly from your installation. You should also check any warranty requirements to confirm that the system is still compliant. You might need to get the system repaired once a year, for example.

For Longer Life of Your Heat Pump

Electricity Tariff

Your electricity company charges you for the electricity you consume according to an electricity tariff. It usually consists of a price per kilowatt-hour (kWh) of power consumed, as well as a daily standing fee. Because heat pumps depend on energy, obtaining a low-cost electricity tariff can help you save money on your monthly bills.

Which one should you choose?

These two forms of heat pumps, ASHP and GSHP, have different configurations and needs, despite their similarity in how they work. Both include energy-saving features that could help you save money and heat your home more efficiently.

It may be easy to pick between an air source and a ground source heat pump if your budget or space is limited, but others will need to spend more time to thoroughly assess their household’s demands. Any potential installer should be able to go over all of these concerns with you in further depth in order to assist you in finding the best solution for your requirements.