A heat pump extracts heat from the outside and transfers it into your home. It requires electricity to operate, but it delivers more heat than the energy it consumes. Since the heat pump only captures heat that already exists in the environment, it doesn't burn any fuel and doesn't produce any carbon dioxide emissions.
Well, everything around us has thermal energy or heat. Normally, heat flows from a warmer place to a colder place. However, to provide heat energy in a home when outdoor temperatures are colder, we need heat to move in the opposite direction – from a colder place to a warmer place. But how does that happen? Here comes the science: when the pressure of a gas goes up, the temperature also increases. In contrast, when the pressure drops, the temperature decreases. This relationship between pressure and temperature is the key to how a heat pump works.
A heat pump works by using energy from the environment and electricity to compress a gas [1], which is called a refrigerant. This process increases the pressure and, in turn, the temperature of the refrigerant [2]. The heat from the refrigerant is then transferred to your home through a heat exchanger, which cools it down slightly [3]. The refrigerant is then allowed to expand, which causes it to cool down even further [4]. Once it has cooled sufficiently, it can absorb more heat from the outside and the process begins all over again.
The heat that is delivered to the heat exchanger can be used to warm your home. This can be achieved through a central heating system or by using warm air in either an air-to-air heat pump or an exhaust air heat pump.
An air source heat pump (ASHP) is a device that provides heating and cooling by absorbing heat energy from ambient air. The process starts with the cold refrigerant in the outside unit, known as an evaporator. Fans blow air across a heat exchanger, where the refrigerant absorbs heat energy from the air. Despite the cold temperature of air during winter, there is still plenty of energy available due to the large volume of air passing over the heat exchanger.
A ground source heat pump (GSHP) is an energy-efficient way to heat a house. It works by collecting heat energy from water that circulates in underground pipes. This water, known as "brine," is mixed with antifreeze and pumped to a heat exchanger inside the house. The heat from the brine is then transferred to the refrigerant, which continues to circulate around the compressor circuit.
Water source heat pumps (WSHPs) function by extracting heat from a body of water and converting it into energy to heat your home. They use a network of submerged pipes filled again with a working brine fluid to absorb the heat from a lake, large pond or river.
Heat pumps are a type of heating system that are more efficient than others because they produce more heat than they use electricity. This efficiency is measured by a metric called the Coefficient of Performance (CoP), which is the amount of heat produced for every unit of electricity consumed. For example, if a heat pump has a CoP of 3.0, it will produce three units of heat for every unit of electricity used.
To better understand the CoP calculation, consider a 14-kilowatt (kW) heat pump. This heat pump has an electrical power input of 4 kW, a heat output of 20 kW, and obtains the remaining 16 kW from the environment. To calculate the CoP, you divide the heat output by the electrical input, which in this example results in a CoP of 5.
Every heat pump has a datasheet that displays its measured CoP, which is determined based on a single point in time and specific test conditions. However, this figure may not always be useful in understanding the cost of running the heat pump in the real world, as the heat pump experiences temperature variations throughout the year due to changing ground or air temperatures. To address this, a Seasonal Coefficient of Performance (SCoP) or Seasonal Performance Factor (SPF) is used to show the efficiency of the heat pump over the course of a year.
To calculate the SCoP or SPF, the heat pump installer must consider various factors, such as the system design for your home, the average temperatures in your area, and the size of your radiators. With this information, the installer can provide you with a better estimate of the heat pump’s performance and running costs throughout the year. Therefore, it is important to obtain the SCoP or SPF before installing a heat pump to understand what to expect in terms of efficiency and costs.
Although compressors and pumps require electricity to operate, they consume less electricity than the amount of heat they move from outside to inside. The efficiency of heat transfer and electricity consumption depends on the difference between the source temperature and the output temperature, which varies throughout the year due to changes in outside temperatures.
Several factors determine how much the use of a heat pump will affect your energy bill, including the type of fuel you are replacing and its costs, your electricity tariff, the type and efficiency of the heat pump, the design of your central heating system, and the average air or ground temperatures in your location throughout the year.
For those replacing gas boilers, heat pumps may be slightly more expensive to run unless the heat pump is installed using a best-practice radiator or underfloor heating design for maximum efficiency. However, as utility prices fluctuate over time, heat pumps are expected to become the cheapest and lowest carbon form of heating available.
For those using LPG or oil boilers, annual variations in prices of LPG or oil make it challenging to provide an exact estimate of annual heating costs. For instance, the cost of heating oil has fluctuated between 40-65 pence per litre over the last five-year period, with an overall upward trend in prices. Unless you can purchase oil or LPG at the lowest possible price to cover your annual use, heat pumps should help you save money on running costs, provided a well-designed system is installed.
The heat pump's compressor has to work harder when there is a greater temperature difference between the outdoor source temperature and the water temperature required for your home's heating system. To reduce the electricity consumption of the heat pump, it is possible to design a low-temperature heating system for your home. By using radiators with a larger surface area or underfloor heating, more heat can be delivered into the room without increasing the water temperature. Running the heating system for longer is another way to deliver more heat into the room with lower-temperature water.
If you have radiators in your low-carbon home with a smaller surface area, the heat pump will have to run at a higher temperature, which means the compressor has to work harder to deliver the same amount of heat as it would with larger radiators or if it had more time to run. Since the compressor works harder, it consumes more electricity, making the system more expensive to run.
To reduce the running costs, it is essential to design a well-planned heating system that minimizes the heating water temperature. The closer the required temperature is to the source temperature (outside air or ground temperature), the more efficient the heat pump will be.
When it comes to standard air-to-water or ground-to-water heat pumps, it is essential to have a hot water cylinder that can store hot water for when you need it. The size of the cylinder required depends on your specific needs, but it can often be installed in a cupboard measuring 80x80cm. The cylinder gradually heats the water, which is then stored for later use.
While most heat pumps can provide water at 55°C, the hot water in the cylinder needs to reach 60°C or higher periodically to kill harmful bacteria. Some heat pumps can deliver water to this temperature, but most systems use an immersion heater within the cylinder to top up the temperature when necessary.
An air-to-air heat pump does not generate hot water, so you will need to find an alternative way to heat your water, such as using an immersion heater.
If you don't have space for a hot water cylinder, hybrid systems are available where the heat pump provides space heating while the boiler provides hot water instead. Another option is to install a heat battery, which takes up less space than a hot water cylinder. Instantaneous hot water heaters are also available that can be installed under your kitchen sink to provide a smaller volume of hot water.
Many conventional fossil fuel boilers were designed to deliver water to your radiators at 75°C. However, modern condensing boilers should ideally run at lower temperatures to increase efficiency. A heat pump is an alternative that would ideally circulate hot water at temperatures between 35°C and 45°C to your radiators or underfloor heating. This is when the heat pump will work most efficiently with the lowest running costs.
If you want to install underfloor heating after the house has already been built, it can be challenging. Instead, you may opt to install a heat pump and continue using existing radiators at a higher temperature or install radiators with greater surface area to provide enough heat using lower water temperatures. Radiators come in many different shapes and sizes. Often, single panel radiators can be swapped for double or triple panel radiators to increase surface area without needing to increase the amount of wall area taken up. Upgrading to triple panel radiators from single panel radiators can more than triple the heat output without taking up more wall space. Radiator upgrades can be a cost-effective way of improving the efficiency of your heat pump and reducing running costs.
Underfloor heating should be designed to work with water no warmer than 45°C in most cases. Therefore, it’s safe to assume that if you have underfloor heating, it should work well with a heat pump. However, some wet central heating systems installed in the 1970s have a particular type of pipe called ‘microbore,’ which has a small internal diameter. This can be problematic when upgrading to a heat pump, as the heat pump cannot transfer water quickly enough to the radiators. If you think you have microbore pipe, speak to your installer when they come to survey your house.
To calculate the energy required to heat your home, your heat pump installer will consider its size, level of insulation, and draught-proofing. Improving your home's insulation makes it more comfortable and lowers heating costs. When a home is well insulated, each room needs less heat to stay warm. This allows radiators to provide heat using lower-temperature water, making the heat pump run more efficiently. This saves energy and money by reducing the heating requirement and increasing the heat pump's efficiency.
Moreover, reducing your overall heating need could mean you require a smaller heat pump, with lower running and purchase costs. Draught-proofing can also reduce your overall heating need by minimizing heat loss through uncontrolled ventilation.
In some cases, increasing insulation may be impractical or expensive. In such cases, insulation installers can visit your home and suggest rooms that could benefit from appropriate insulation. If you live in an older home built before 1919, or in a listed building or conservation area, we recommend consulting insulation specialists with experience in working with such properties.
If you cannot install insulation or increase the radiator size, alternatives are available. Some heat pumps are specifically designed to deliver water at a higher temperature. Your installer should be able to design a system that works for your needs. You could also consider a hybrid system.
Before installing a heat pump, it is crucial to check whether you need to seek permission from your local planning authority. Most heat pump installations fall under the category of ‘permitted developments,’ which means that no permission is required. However, there are exceptions to this rule, especially if you live in a listed building or conservation area. It is therefore advisable to consult with your local planning department before proceeding with the installation.
In addition, it is essential to inform your local district network operator (DNO) that you plan to install a heat pump. The DNO is responsible for delivering electricity from the network to your home. You can ask your installer to assist you with this process, as they will have all the necessary information to complete the forms.
If you want to know more about informing a DNO (Distribution Network Operator) about your heat pump installation, you can check out the 'Connecting electric vehicles (EVs) and heat pumps' section in this Energy Network Association guide. https://www.energynetworks.org/operating-the-networks/connecting-to-the-networks/
Additionally, you can find further information about registering a heat pump, solar panels, electric batteries, and electric vehicle chargepoints in England, Scotland, and Wales on the UK Government website.
https://www.gov.uk/government/publications/register-energy-devices-in-homes-or-small-businesses-guidance-for-device-owners-and-installation-contractors/register-energy-devices-in-homes-or-small-businesses-guidance-for-device-owners-and-installation-contractors
1. Finding a good installer: It is always recommended to get quotes from at least three different installers. You should ensure that the installers are well-qualified to do the installation. More advice on finding a good installer can be found on our website.
2. Maintenance: Like any other heating system, a heat pump needs to be well maintained to operate as designed. However, most heat pumps are easy to maintain with minimal input required from the end user. Workmanship warranties for heat pumps can last up to 10 years, and many manufacturers offer options for warranty extensions for a fee. With regular scheduled maintenance, you can expect a heat pump to operate for 15 years or more. Some typical checks include visual inspections of the water pump, external pipes, fittings, and electronics. Ground source heat pumps may also need to be re-pressurized or have the quality of the antifreeze checked, which can be done by a professional every 2-3 years. You should ask your installer for written details of any other maintenance checks you should undertake to ensure everything is working correctly. You should also check any requirements under your warranty to ensure that the system remains compliant. For example, you may need to have the system serviced each year.
3. Controls: To ensure that your heat pump performs at its highest capacity, it is important to use your controls effectively. Depending on the controls you have and the level of heating and hot water you need, there are different ways to get the most from your heat pump. You can find more guidance on how to set the system controls on our blog/Page.
4. Electricity Tariff: An electricity tariff is how your energy supplier charges you for the electricity you use. It is typically made up of a price per unit (kWh) of electricity you consume and a daily standing charge. Since heat pumps use electricity, finding a low-cost electricity tariff can help keep your running costs low. More information about choosing an electricity supplier and tariff can be found on our website.
Air source heat pumps are the most common type of domestic heat pump in the UK and are suitable for many types of homes.
If you have a garden or large outdoor space, you may be interested in finding out more about ground source heat pumps. You will need access to a river or lake for a water-sourced heat pump, so these are rare in the UK.
If you don’t have radiators or underfloor heating, and can’t or don’t want to install these, you might be interested in finding out more about air-to-air heat pumps. Air-to-air systems are more commonly associated with smaller properties such as flats and park homes. You can find more information on the differences between ASHPs and GSHPs on our website.
There are numerous types of heat pumps and general Low-Carbon heating products. Our guides are here to help you move towards a Low-Carbon future.
