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Frequently Asked Questions About Air Source Heat Pumps

Published on 22 May 2024

Posted in Advice & Reviews

by MKM

7 min read

Air Source Heat Pumps(ASHPs) are a more sustainable way to heat a home or building and are becoming more popular in the UK domestic market. They take the heat from the air outside and transfer it, via the water in the heating circuit, to the air inside a property.

To help you understand more about ASHPS, we have complied a handy list of FAQs:


How do Air Source Heat Pumps work?

Air source heat pumps work by extracting heat from the outside air and transferring it indoors to heat a building. They use a refrigerant cycle involving a compressor and a condenser to absorb heat from the outside air, even at low temperatures, and release it inside.


What temperature do air source heat pumps work at? 

Using a variety of refrigerants means that ASHPs can be effective (more than 100% efficient) down to temperatures as low as -25˚C.

Most ASHPs on the market will heat water up to 55˚C but are most efficient at 35˚C. Newer, high temperature models that will heat water to 65˚C and beyond are becoming more readily available.


Are Air Source Heat Pumps any good?

Yes! However, if you have an older home (pre-1990s) that is not well insulated, investing in draughtproofing and insulation to make your home more efficient before installing an air source heat pump is advised. In addition, ASHPs work well with a larger surface area of underfloor heating, and more efficient/ low temperature/ larger radiators. You may also want to consider incorporating Solar Thermal Panels into the ASHP system to heat your hot water as this can increase the efficiency.


Are Air Source Heat Pumps noisy?

Heat pumps are about as loud as a boiler or a fridge. The noise range for a modern fridge freezer is 32 to 47 decibels. Plus, some of the more modern Air Source Heat Pump designs have been awarded the Quiet Mark.


Can Air Source Heat Pumps be wall mounted?

An ASHP can be floor standing, on a plinth or wall mounted using brackets.  You’ll need to have enough air flow round the intake on the unit, and it must be level and secure. Your installer will advise what the options are for your property.


Is an Air Source Heat Pump expensive to install?

As with any installation, the price will depend on the type of product installed. Where ASHPs differ to boilers is that they are subsidised by the government. If you were to install an ASHP now you would be able to receive a fixed payment under the Boiler Upgrade Scheme (BUS) of up to £7,500.


Will Air Source Heat Pumps get cheaper?

As ASHPs become more popular and are produced in larger quantities, it’s likely that prices will come down.


Are Air Source Heat Pumps expensive to run?

Modern ASHPs also use inverters to allow them to modulate, this helps improve their efficiency, ultimately bring down the running cost. To check how ASHPs compare you need to know the seasonal coefficient of performance (SCOP) of the model. This gives the average over a year, allowing for fluctuations in air temperature. As a comparison, a gas boiler has a coefficient of performance (COP) of up to 0.9, although this can decrease with the life of the boiler if it’s not maintained or set up correctly. If you have correctly specified the system, then you can expect it to save you money compared to a fossil fuel powered alternative.


How do I buy an ASHP?

All MKM branches can order Air Source Heat Pumps for customers, but you will need a qualified installer to create the right specification and fit the system. View the range online today. 


What maintenance is required for Air Source Heat Pumps?

As ASHPs use an outdoor unit, it will require periodic inspection by the homeowner to remove debris, like leaves, from the unit. Apart from that, ASHPs will require an annual service, much like a boiler, to maintain peak efficiency and any manufacturer’s warranties.


How efficient are Air Source Heat Pumps?

ASHPs efficiency and effectiveness is determined by how much heat they produce vs the electricity used to power them. To tell how efficient a ASHP is you would look at the COP (or SCOP for its annual performance) of the model. As an example, a COP of 4.41 means that for every 1kW of electricity used, the ASHP will generate 4.41kW of heat. COP improves as the outside air temperature increases or the water temperature in the heating circuit decreases.


Can I just replace my current boiler with an Air Source Heat Pump?

There are two factors to bear in mind to help you decide whether you can just replace your current boiler which are;

  • The level of insulation in your home
  • Whether you are looking at a high temperature Air Source Heat Pump. This means you would be able to use your existing radiator circuit.


Why are my radiators cold with an Air Source Heat Pump?

ASHPs heat water to a lower temperature than traditional oil or liquid petroleum gas (LPG) boilers, typically 45˚C to 50˚C. Homeowners often require a period of adjustment, the radiators will still be hot but not as hot as they were. ASHPs are designed to provide a constant temperature so there is less of a requirement to have really hot radiators. If you are using radiators, you will more than likely need to upgrade these to provide enough heat for the rooms they are used in.


How do I know if an Air Source Heat Pump is suitable for my property?

Not all properties will be suitable for ASHPs and the majority will likely need some improvement in insulation to make them cost effective. An energy performance assessment would need to be carried out in conjunction with a full heat loss calculation and system design to determine the correct course of action.


Do Air Source Heat Pumps require specialist installation?

This depends on the type of system being installed. A monobloc system can be installed by any plumber as they don’t use refrigerant gas. However, it is recommended that installers are trained by the manufacturer of the product, so they are familiar with any specific requirements.

A split system can only be installed by somebody who has specialist training as it involves the use of refrigerant gas. If you are applying for funding, then the system must be installed by an accredited installer or firm.


Will an Air Source Heat Pump provide me with hot water?

The quick answer is yes, although you will need to install a specialist heat pump cylinder as an Air Source Heat Pump will not provide hot water on demand like a combi boiler. You cannot use a standard cylinder as the heating coil is not big enough to provide enough heat transfer. Heat pump cylinders are manufactured using longer and wider coils to allow for the lower water temperature. If they heat below 60˚C, then there will need to be an anti-legionella cycle built into the system to allow for an increased heat cycle to prevent this from happening.


How long do Air Source Heat Pumps last?

A properly maintained Air Source Heat Pump system should last over 20 years before it needs replacing.

Although, you need to make sure that you have the right equipment for the location. For example, locations by the coast are subject to higher levels of salt in the air which will degrade the equipment quicker. To counter this, you can get the evaporator coil coated with a special treatment to protect it from the increased likelihood of corrosion.


Will I need a buffer vessel to an Air Source Heat Pump?

This will depend on the type of installation you have but a buffer vessel acts as an additional energy store and can help reduce cycling. They are also useful when the Air Source Heat Pump has a defrost cycle as it can help stop the system from pulling heat from inside the property.


For further information on Air Source Heat Pumps, visit your local MKM branch