Air Source Heat Pumps & How They Work: A Comprehensive Guide

Updated on 11th November, 2022 by Martin Astley

If you’re looking for a more energy-efficient way of heating your home, an air source heat pump (ASHP) could be an ideal solution.

With a gas boiler ban potentially on the way, many of us will need to change the way we heat our homes.

Highly efficient and typically inexpensive to run, an air source heat pump is a great alternative to gas heating.

What is an Air Source Heat Pump?

An air source heat pump is a renewable energy source which extracts heat from the outside air in order to provide heating and hot water to your home.

These systems are highly effective. They can absorb heat from temperatures as low as -15°C – so you don’t have to worry about their performance deteriorating during colder seasons.

Air source heat pumps do require some electricity to run, however, their renewable heat output is greater than their electricity input, so they are still regarded as an energy-efficient source of heating.

Types of Air Source Heat Pumps

There are two main types of air source heat pumps. These include:

1. Air-to-water – These systems are the most common type of air source heat pump in the UK. They extract heat from the outside air and use this energy to heat water. This heated water is then transported through to your central heating system and distributed as needed.
2. Air-to-air – This form of air source heat pump absorbs heat from the outside air and then transfers this heat to your home through the use of a fan system. Unlike air-to-water systems, air-to-air ASHPs do not provide hot water as well as heating.

How Does An Air Source Heat Pump Work?

The heat generation process for air source heat pumps can be likened to a reversed version of a fridge’s cooling process. Outside air is blown over a refrigerant which is pumped between two heat exchangers on a loop. This refrigerant has a low boiling point and turns into a gas once it takes on the heat energy from the outside air.

This gas is then passed through a compressor, which increases its heat and pressure. Once this is completed, the gas is sent through a heat exchanger and the heat is transferred and used to heat up either water or air for heating and/or hot water purposes within your home (depending on whether it is an air-to-water or air-to-air system).

In the final stage of the heating process, the liquid refrigerant is sent through an expansion valve which reduces its pressure and temperature, then the cycle starts over again.

What Are The Pros And Cons Of Air Source Heat Pumps?

To help you decide whether an air source heat pump is suitable for your home, below we outline some of the main advantages and disadvantages of this type of heating.

Pros

• Energy Efficiency – As energy is generated from a natural source instead of fossil fuels, ASHPs emit far less greenhouse gasses than other forms of heating (e.g. boilers).
• Cost-effective – Less energy consumption could lead to lower energy bills and help you maximise your savings!
• Simple installation – Air source heat pumps are usually easy to install. They are particularly simpler to install than ground source heat pumps, which typically cause some upheaval.
• You could earn an income through the Renewable Heat Incentive (RHI) – Households with a water-to-air heat pump installed are eligible for quarterly cash payments (over seven years) through the government’s Renewable Heat Initiative scheme.
• Can be paired with other renewable sources – To boost the energy-efficiency of your ASHP system, you could power it using solar panels or wind turbines. This is a more sustainable option than using energy from the grid which is sourced from fossil fuels.
• Low maintenance – ASHPs don’t usually require significant maintenance, you simply need to ensure that it receives a regular service.
• Long lifespan – Air source heat pumps can have working lives of up to 20 years. This will depend on the quality of its maintenance.

Cons

• Reduced heat supply – Air source heat pumps deliver heat at lower temperatures in comparison to boilers. You may therefore have to invest in larger radiators and improve your property’s insulation in order to get the best quality of heat.
• Further installations may be required– Air source heat pumps are known to work well with underfloor heating, as high temperatures are not required. If you decide to get underfloor heating installed with your ASHP, your overall installation costs will increase.
• Noisy operation – In contrast with modern boiler systems, ASHPs can emit some noise during operation. However, technology is constantly evolving, so modifications could be made to reduce their noisiness in the future.
• Low temperatures can impact performance – Although these systems are designed to work with temperatures as low as -15°C, their efficiency levels can reduce when temperatures reach below 0°C.
• They require electricity – Despite air source heat pumps being more efficient than other forms of heating, they still require some electricity to function. So, they are only semi-renewable. This makes them a potentially unsuitable choice for homeowners who want to make their household entirely sustainable.

A potential solution for this is to pair your ASHP with another renewable energy source like solar panels or wind turbines. This way the electricity is generated naturally.

How Much Do Air Source Heat Pumps Cost To Install?

Air source heat pump installation cost on a property is typically between £9,000 – £11,000. Your installation price will be affected by the conditions of your existing heating system and the complexity of the installation process. Costs may be more expensive than boiler installations, but ASHPs are cheaper to install than ground source heat pumps.

In the past, air source heat pumps have been most popular with new build properties, as it can be difficult to retrofit existing properties for their installation. An ASHP installation can require new radiators, pipework modification and/or underfloor heating – this will all come at an additional cost.

The running costs of your air source heat pump system will depend on the size of your property, its level of efficiency, the quality of its insulation and the temperatures desired.

The amount of savings you can make from your air source heat pump will be influenced by your heat distribution system, your fuel costs (i.e. your chosen energy tariff), whether you require water heating from the system, and whether you will be using controls (this is recommended).

In terms of maintenance costs, an annual service for an air source heat pump can cost approximately £200.

Is There Any Government Funding Available For Air Source Heat Pumps?

Government funding schemes are available to help homeowners with the cost of installing energy efficient solutions like air source heat pumps. Available funding options include:

1. Green Homes Grant Scheme – Through this funding scheme, you could receive vouchers for up to two thirds of your air source heat pump’s installation costs. Contributions can be up to £10,000, depending on your eligibility.
2. Renewable Heat Incentive – This incentive scheme provides homeowners with quarterly payments throughout seven years for the heat they generate through renewable systems. Eligible heating systems include air source heat pumps, ground source heat pumps, solar panels and biomass boilers.

Is An Air Source Heat Pump Suitable For My Home?

If your home is well insulated and/or you currently have underfloor heating, an air source heat pump could be a great option for you.

Air source heat pumps are also well suited to homes that are not connected to the national grid. Despite their higher installation costs, they are cheaper to run than using electricity, oil or coal for space heating.

Homeowners with properties of all types and sizes are likely to consider air source heat pumps more over the next few years. This is due to government efforts to increase heating efficiency in UK homes and eradicate heating forms that emit greenhouse gasses into the atmosphere, such as gas central heating.

The government has strict targets to reduce carbon emissions to net-zero by 2050 and promoting the use of renewable energy sources like air source heat pumps in the UK is just one of the ways in which they plan on achieving their efficiency goals.

Frequently Asked Questions (FAQs)

Is an air source heat pump worth it?

For many people, an ASHP is a very sensible investment as its pros (such as affordability and efficiency) outweigh any cons (such as reduced heat supply.) For anyone concerned with reducing their carbon footprint an ASHP is a very worthwhile investment.

Is an air source heat pump cheaper than gas?

Although the environmentally friendly alternative promises lower energy bills than gas, the installation and maintenance take away from the saving. So overall, an air sour heat pump may be as expensive, if not more, than gas.

Can air source heat pumps work with radiators?

Air source heat pumps do work with radiators. Due to the low flow temperatures, the heat emitting surface area should be bigger than for boiler-operated heating. This means existing radiators might not be suitable and you should install new ones.