Air source pumps are an alternative way to heat your home, and could be the ideal solution if you want to generate your own heat and potentially save money on your energy bills. 

Aside from air source heat pumps, there are other options available if you want to generate your own heat – such as wood burning stoves and solar panels. Read on to find out more about air source heat pumps, including their pros and cons, so you can decide whether getting one is right for you.

How an air source heat pump works

An air source heat pump is usually placed outdoors at the side or back of a property. It takes heat from the air and boosts it to a higher temperature using a heat pump. The pump needs electricity to run, but it should use less electrical energy than the heat it produces.

Many air source heat pumps are eligible for payment through the Renewable Heat Incentive, a government scheme that provides payments to homeowners who generate their own heat.

Air-to-water heat pumps

Air-to-water heat pumps take heat from the outside air and feed it into your wet central heating system. As the heat produced is cooler than that from a conventional boiler, you may need to install larger radiators or underfloor heating in your home to make the most of it.

  • Air-to-water ASHPs work better with underfloor heating systems. If underfloor heating is not possible, large radiators should be used. This is because the heat generated by the heat pump is not as high as that produced by a conventional boiler, so a larger surface area is needed to achieve similar temperatures in your home.
  • Air-to-water heat pumps could be better suited to new-build properties than retrofit. This is because costs could be reduced if the heat pump is included as part of the building specification, rather than having to retrofit underfloor heating later on.
  • Heat pumps can save you more on your heating bills if you’re replacing an electric, oil, LPG or coal system, rather than gas.
  • A well-insulated home is essential – otherwise the heat the pump is generating escapes more easily.
  • Once in place, the heat pump should require little maintenance.
  • Air-to-water heat pumps qualify for the Renewable Heat Incentive.

Air source heat pump costs and savings

ASHPs are cheaper than ground source heat pumps. The Energy Saving Trust (EST) estimates that the cost of installing a typical ASHP system ranges between £7,000 and £11,000.

The payback period (the time taken to recoup the cost of the system in energy savings) depends on how efficiently your system works, the type of heating system you’re replacing, whether you can get money with the RHI and how you’ll be using the heat generated by the pump.

If replacing an old heating system, the EST says that an average performing air source heat pump in a four-bedroom detached home could save:

  • Replacing oil (non-condensing) – between £290 to £315
  • Replacing gas (non-condensing) – between £455 to £485
  • Replacing LPG (non-condensing) – between £1,000 to £1,090
  • Replacing electric (old storage heaters) – between £735 to £820

The EST also estimated the RHI would pay an extra £1,140 to £1,235 a year.

But if you’re replacing a new heating system, an air source heat pump could actually work out more expensive:

  • Replacing a new (A-rated) gas boiler – £10 to £15 bill increase
  • Replacing a new (A-rated) oil boiler – £155 to £165 bill increase

Installing an air source heat pump

ASHPs look similar to air-conditioning units. They are less disruptive to install than ground source heat pumps, as they do not require any digging in your garden.

An ASHP works a bit like a refrigerator in reverse. The process consists of an evaporator, a compressor and a condenser. The ASHP absorbs heat from the outside air into a liquid at a low temperature, then the heat pump compressor increases the temperature of that heat. In the condenser, the hot liquid’s heat is transferred to your heating and hot water circuits. So you can use it to warm up your home.

In the summer, an air-to-air heat pump can be operated in reverse. So it can be used like an air-conditioning unit to provide cool air for your home.

Pros of air source heat pumps

  • Air source heat pumps can generate less CO2 than conventional heating systems.
  • They are cheaper than ground source heat pumps, although their efficiency can be lower.
  • Air source heat pumps are also easier to install then ground source heat pumps, particularly for retrofit.
  • ASHPs can provide heating and hot water.
  • They require very little maintenance.
  • Some can be used for air conditioning in the summer.
  • ASHPs can qualify for the RHI, a financial incentive that pays you for generating your own heat through renewable technology.
  • You need to use electricity to power the pump which circulates the liquid in the outside loop. But for every unit of electricity used by the pump, you get between two and three units of heat – making this an efficient way to heat a building.
  • Cheaper Economy 7 electricity tariffs can be used to lower the cost of electricity to power the heat pump.

Cons of air source heat pumps

  • You’ll need enough space in your garden for the external condenser unit (comparable in size to an air-conditioning unit).
  • Condenser units can be noisy and also blow out colder air to the immediate environment.
  • You still need to use electricity to drive the pump, so an air source heat pump can’t be considered completely zero-carbon unless this is provided by a renewable source, such as solar power or a wind turbine.

Alternatively, consider solar photovoltaic panels or a wind turbine (if you are in a suitable area) for a greener source of electricity

How green are air source heat pumps?

An air source heat pump system can help to lower your carbon footprint as it uses a renewable, natural source of heat – air. The amount of CO2 you’ll save depends on the fuel you are replacing. For example, it will be higher if you are replacing electric heating rather than natural gas.

A heat pump also requires a supplementary source of power, usually electricity, to power the heat pump, so there will still be some resulting CO2 emissions.

Ground source heat pumps are also available. They draw heat from the ground via a network of water pipes buried underground, usually in your garden.

Heat pump energy labels

New regulation means that heat pumps will now have to have an energy label on them.

The label gives information about the energy efficiency of the heat pump and rates products from dark green (most efficient) to red (least efficient).

All new heat pumps must be sold with an EU product label, since 26 September 2015. The installer should also produce a package label that displays the efficiency based upon several different components in the heating system.

After 25 March 2016, all heat pumps certified by the Microgeneration Certification Scheme must be sold with a product label, and the installer must produce a package label. If your heat pump is not sold with a product label it may not be eligible for the RHI.

How does a heat pump work?

The simple answer is that it’s like a fridge in reverse. Heat from the air is absorbed at low temperature into a fluid. This fluid then passes through a system of heat exchangers and compressors with a refrigerant, which multiplies this up to heat which is enough to provide hot water for your heating system and also all of the hot water for your taps.

Is a heat pump suitable for me?

  • Do you have somewhere to put it? You’ll need a place outside your home where a unit can be fitted to a wall or placed on the ground. It will need plenty of space around it to get a good flow of air. A sunny wall is ideal.
  • Is your home well insulated? Since air source heat pumps work best when producing heat at a lower temperature than traditional boilers, it’s essential that your home is well insulated and draught-proofed for the heating system to be most efficient.
  • What fuel will you be replacing? The system will pay for itself much more quickly if it’s replacing an electricity or coal heating system. Heat pumps may not be the best option for homes using mains gas.
  • What type of heating system will you use? Air source heat pumps can perform better with underfloor heating systems or warm air heating than with radiator-based systems because of the lower water temperatures required.
  • Is the system intended for a new development? Combining the installation with other building work can reduce the cost of installing the system.

Does it work in winter?

Hitachi systems that are designed for you are sized to meet the entire heat loss of your house and to deliver all the heating and hot water that you require. The heat pump itself will work perfectly well, even in the middle of winter when it’s well below freezing outside.

Do I need a big system?

One of our recommended installers will carry out a full survey but as a rule of thumb, if you look at the number of litres of oil you have used on average over the past couple of years and multiply this number by 10, then divide by 2,400 to give a rough idea of the heat pump size in kW that you might need.

For example, if you used 2,000 litres of oil, that would be 8.3 – i.e. you might need a 8.5kW heat pump. The heat pump size may well be less if you have an old boiler, as this is likely to be less efficient.

Won't it cost the earth to install and run?

This obviously depends on how much heating you use. For a 4 bed house, it might cost £9,000 for an air source heat pump and remember the combination of your heating savings and the RHI will usually allow you to get your money back in five years or less.

What sorts of properties are suitable for an air source heat pump?

Air source heat pumps are a suitable complete or partial solution for the majority of existing houses as well as new builds. Most properties that can achieve a reasonable level of thermal insulation could be suitable for an air source heat pump. In order to achieve the highest levels of efficiencies, all properties should have been updated with the basic thermal improvements i.e. cavity wall installation, loft insulation and double glazing. The air source heat pump then needs to be able to meet the maximum heat demand of the property under its maximum (coldest) conditions.