Air Source Heat Pump FAQs

What is a heat pump?

A heat pump uses the principles of thermodynamics to absorb energy from the surrounding environment and converts it into usable energy which can provide heating for our homes.

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How do air source heat pumps work?

There are two types of air source heat pump – ‘air to air’ and ‘air to water’. The Grant Aerona³ uses an air to water system which utilises heat energy captured from the air in ‘wet’ heating system radiators or underfloor heating.

The process uses the same vapour/compression cycle that extracts heat in a domestic fridge. A refrigerant with a low boiling point is exposed to external air temperatures in an evaporator. The liquid boils off to a gas and absorbs the latent heat energy of the air. This gas is then compressed increasing the heat content in the refrigerant, before passing through a heat exchanger where it condenses back to a liquid state while transferring the heat to the water of the heating system. The liquid refrigerant is then re-circulated through the evaporator and the cycle is repeated.

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Is an air source heat pump good for the environment?

Yes, the heat source used by Grant Aerona³ heat pumps is entirely renewable which helps reduce the amount of harmful greenhouse gases being released into the atmosphere and, in so doing, lowers the carbon footprint of the household. Heat pump renewable energy is just one way households can lower their carbon emissions. 

Is my home suitable for an Air Source Heat Pump?

This depends on several things such as how well your property is insulated and ventilated. The closer your property is to satisfying new build property standards and regulations, the more likely your property will be suitable for a heat pump installation. You will also need adequate space outside your home for the heat pump to be installed. Furthermore, an air source heat pump needs free air space around it to get a good flow of air as you do not want the air that has already passed across the evaporator (inside the heat pump) to be recirculated because this will compromise the performance.

It is important to remember that a heat pump will not perform as well in poorly insulated properties. Dwellings need to be well insulated for heat pumps to be effective – air source heat pumps produce lower temperature heating so it takes longer to initially get the property warm. It is then important that this heat does not escape through poorly insulated windows, walls or the roof as this can result in the system using more energy to reach the desired temperature.

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How do I prepare my home for a heat pump?

For a heat pump to work most efficiently, your home needs to be well insulated to prevent as much heat from escaping as possible. Insulation improvements come in many forms such as attic, wall and floor insulation, and window, door and ventilation upgrades.

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What space do I require for an air source heat pump?

An air source heat pump needs to be located outside in the open air and sufficient space must be allowed around the unit (1000mm from front and sides, 300mm from back) so air can flow freely into it. The unit also needs to be installed on a flat trowelled finished concrete base 150mm thick and this base should extend at least 100mm beyond the unit on three sides. Full details are given in the Installation and Servicing instructions supplied with any Grant Aerona³ air source heat pump.

Where should I site an air source heat pump?

A heat pump will perform better on a south facing elevation as it will be exposed to warmer ambient temperatures because of the orientation of the sun. The north face of a building will usually have colder ambient air than any other side so, to ensure maximum efficiency from a Grant Aerona heat pump, position the unit on a warmer side and preferably south facing. 

Ground level is preferable but not essential as this allows ease of access for servicing and maintenance. Shielding of the heat pump is acceptable providing the minimum clearances set out in the manual are adhered to. All heat pumps make a noise so take opening windows and doors into account as well when considering the final position of your heat pump.

Can a heat pump be installed in a shed or other building?

No, an air source heat pump cannot be installed indoors. They need to be sited outdoors with a clear, unobstructed airflow in order to work. You can learn more about how an air source heat pump operates here.

What is R32 refrigerant and what is the benefit?

Grant’s latest generation of air source heat pumps uses R32 refrigerant which has a GWP which is considerably lower than other typical heat pump refrigerants such as R410. In addition to having a lower GWP figure of 675, R32 is a single-component refrigerant which means it has no temperature glide. Refrigerant blends that have two or more components exhibit temperature glide but as R32 only has one molecule in its formation, its saturated liquid and vapor temperatures are the same. By removing the risk for the refrigerant to suffer from glide, the system can recharge and recycle with greater ease, making it more efficient.

Do I need planning permission for a heat pump?
All Aerona³ heat pumps are less than 0.6m³ in volume and fall within permitted development for the unit. That is one less thing to consider when working to meet the permitted development requirements, however do keep in mind that there are other requirements to meet which are site specific e.g. where the units will be located, how many there are and the status of the building/land concerned (listed building, etc.). You should always check with your Local Authority Planning Department prior to any work commencing.
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Why is it important to size a heat pump correctly?

Air source heat pumps must be correctly sized to ensure that it can provide the required amount of heat output at the design conditions – typically when the outside temperature is at -3°C. To do this an installer must first accurately determine the heat loss from the property and then, using this information, correctly select the required size of heat pump based on the design outside air temperature. Grant UK can assist with sizing the heat pump model and the heat loss of your building.

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What size heat pump will my home need?

Heat pumps vary in size with outputs in Grant’s Aerona³ R32 range available from 6kW up to 17kW. Your installer will carry out a thorough assessment and heat loss calculation of your property in order to specify the right heat pump model selection for your home.

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How do air source heat pumps operate in very cold weather conditions?

During winter months when it is particularly cold, condensation can form and freeze on the finned evaporator coil of the unit. It is a normal occurrence and the heat pump is designed to cope with this. The control system will detect when the coil has iced up and will automatically enter a ‘defrost’ cycle. During this short ‘defrost’ period the fan will stop and the heat pump will cease supplying heat to the heating system in order to melt the ice. On completion the fan and heat pump will automatically restart and resume supplying heat to the heating system. This will not adversely affect the building temperature.

Will a heat pump work when the outside air temperature is below freezing?

Yes, despite some misconceptions, air source heat pumps will continue to work when the outside air temperature falls below 0ºC. Heat pumps, such as Grant’s Aerona³ range, have clever, in-built features which enable the unit to operate successfully even in freezing temperatures.

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Is an air source heat pump noisy?

Heat pumps use either one or two fans to draw air through the unit to extract the heat energy. These fans will produce a moderate sound level that might be perceived by some as a nuisance, either by the occupants of the building with the heat pump system, or the neighbours. In particular this may be a greater problem at night when background noise is much lower. Careful choice of the heat pump location can help to minimise or eliminate the potential nuisance, e.g. not too close to bedroom windows (particularly with a bungalow) or too close to a neighbour’s boundary or property. Two of our latest models, the Aerona³ R32 13kW and 17kW heat pumps have achieved the Quiet Mark, an accolade which recognises some of the quietest, high performing products in the market.

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Will my electricity bills increase with a heat pump?

Your household electricity consumption will increase using an air source heat pump. However there will usually be no gas or oil bill to pay to heat the house, unless a bivalent heating system is chosen (combining the heat pump with a gas or oil-fired boiler as a backup heat source). You should therefore consider the overall cost of heating, i.e. the increased electricity cost compared with the saving in oil or gas bills.

Are Grant air source heat pumps MCS approved?

Yes, all models within the Grant Aerona³ range are MCS approved.

Are Grant heat pumps Keymark approved?

All of the Grant Aerona³ R32 air source heat pumps have been approved by CEN KEYMARK, an independent European certification mark for all heat pumps, combination heat pumps and hot water heaters.

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Are Grant air source heat pumps eligible for the Boiler Upgrade Scheme?

Yes, Grant's Aerona³ air source heat pumps will be eligible for the Boiler Upgrade Scheme grants provided the installation fulfils the eligibility criteria.

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What type of heating system controls are used with Grant heat pumps?

Normal domestic heating controls, such as a 2-channel programmer, room thermostat and cylinder thermostat are suitable for use with Grant air source heat pumps.

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Do air source heat pumps work with normal radiators?

Yes, air source heat pumps can be installed with radiators but the radiators must be correctly sized for the lower water flow temperature. It is important that the system is designed correctly and you can speak to your installer or a member of our Design Team to discuss this further. 

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How much bigger do radiators need to be for a heat pump?

As a rule, you can expect to fit a radiator that is 2½ times larger than a typical radiator that is connected to a gas or oil boiler installation to provide the same heat output.

Can a heat pump be connected to an existing hot water cylinder?

When installing an air source heat pump, a hot water cylinder that is compatible with heat pumps must be selected and, more often than not, an existing cylinder will not be suitable.

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What are the advantages and disadvantages of a heat pump?

It is important that consumers understand that an air source heat pump system differs to a traditional central heating system, such as a gas or oil boiler. They use electricity to power them, they are a low temperature heating system and the system design is different to that of a traditional heating system.

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What is the difference between a Monovalent system and a Bivalent system?

In brief, a Monovalent system is when a heat pump covers the whole heating load whereas a Bivalent system is when a heat pump is combined with another heat source.


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How much does an air source heat pump system cost?

An air source heat pump cost will vary for each installation because every home and property is different. The size of heat pump model required, the type of heat emitter installed and any energy-efficiency measures that may need to be implemented can all affect the cost of installing a heatpump system. Your installer should carry out a thorough assessment of your home, calculating its heating demand and hot water requirements as well as determining the heat loss from your property - this will enable them to provide you with an in-depth quote for a new air source heat pump installation. It is recommended to obtain quotations from more than one installer so to find local heat pump installers near to you, please use our Find an Installer online search.

Can I replace my old boiler with a heat pump?

In many cases, yes, a heat pump can provide all the heating and hot water you need for your home. Depending on the build type of your property, some energy efficiency measures may need to be implemented such as improving the level of controls, property insulation, increasing the heat emitter sizing and pipe sizes.

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Should I replace my gas boiler with a heat pump?

Heat pumps are up to four times more efficient than LPG, oil, electric and gas boilers. An air source heat pump can also ensure that your heating system is more environmentally friendly. Due to fluctuating energy price increases affecting all fuel types (gas, oil, LPG or electric), heat pump running costs will not always be comparable to other heat sources, but nevertheless, this will alter as and when the rates and price of different energy sources change.

Is my existing heating system suitable for use with an air source heat pump?

An air source heat pump operates differently to a traditional fossil fuel heating system, requiring larger surface areas to emit heat into the room and different pipework and connections as well. We would recommend contacting a local heat pump installer who can visit your home and assess your current heating system. They will be able to advise whether new radiators, pipework and/or a hot water cylinder may be needed to accommodate a new heat pump heating system. Find a local G1 heat pump installer here.

Will I save money switching from my current boiler to a heat pump?

It is possible to save money on all fuel types by either improving a home's thermal insulation, reducing the room temperature, shopping around for a better energy deal or upgrading to a more energy efficient heating system.

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Can a heat pump heat my hot water and my house at the same time?

No - air source heat pump systems are not designed to heat rooms (space heating) and hot water (DHW) at the same time. Instead, a heat pump will provide space heating until a demand for hot water is asked for, when the heat pump will then divert to providing hot water. Once the DHW demand stops, the heat pump’s operation will return to heating the home.

Do I have to pay VAT when installing an air source heat pump?

Between 1st April 2022 through to 31st March 2027, the rate of VAT on the installation of certain energy saving materials, such as a heat pump, is 0%. If you have a heat pump installed at your home during this period and you live in Great Britain, you should not have to pay VAT.

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What does an air source heat pump installation look like?

An air source heat pump installation is different to installing a typical fossil fuel heating system. The first step your installer will need to take will be an in-depth assessment of your home, its space heating and domestic hot water requirements, as well as a room-by-room heat loss calculation. Next, the system will need to be correctly designed with the specification of the air source heat pump sizing and heat emitter sizing - your installer will carry out this step and Grant UK's in-house Design and Specification Team can support them. Provided the heat pump installation falls within permitted development for planning permission and once the DNO application is approved, your heat pump's installation can commence. Please note, if you install a Connect and Notify heat pump such as the Aerona³ 6kW, 10kw or 13kW models, your installer will only need to notify your local DNO once the system is commissioned. Every heat pump installation is different so to learn more about your home's specific requirements for a new air source heat pump, please contact local air source heat pump installers. You may also find our vLog here of interest as well, which follows one family as they transition from a gas central heating system to a renewable heat pump. 

Why are the UK government pushing heat pumps?

Installing heat pumps in homes will help improve energy security while also reducing the carbon emissions of domestic home heating here in the UK. Electric heating systems are low carbon solutions which is one of the reasons why the Government is supporting this technology. In a similar way, the UK government are pushing for changes in the motor industry by moving away from diesel and petrol vehicles to electric and hybrid alternatives.

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Are heat pumps popular in the UK?

The popularity of heat pumps is increasing even though they are usually more expensive to purchase than a traditional gas or oil boiler. Historically, there has been a lack of skilled engineers available to install and maintain air source heat pumps, however, the number of qualified air source heat pump installers is rapidly increasing in the UK.

Can I get any grant funding towards the cost of installing a heat pump?

There are a number of different funding schemes available to households in England, Scotland and Wales which can provide financial support to eligible homes looking to improve their energy efficiency and incorporate renewable energy.

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Is the Grant heat pump available in any other colour?

No - all of the models available within the Grant Aerona³ heat pump range are supplied in one colour.

Where can I find a heat pump installer?

To find local air source heat pumps installers in your area, you can use the online search tool available on the Grant UK website. Please click here to research heat pump installation companies near to you.

What is a hot water cylinder?

A hot water cylinder is usually made from stainless steel with insulation surrounding it and an outer casing. Inside the cylinder, there will be one or more coils which transfer the heat generated by the heat source into the water contents of the cylinder. Cylinders are designed to store the hot water which then feeds to the taps in your home. Unless you have a combination boiler, it is likely that you will have a separate cylinder for your domestic hot water. All air source heat pumps, solar thermal systems and hybrid installations require a separate cylinder.


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What size hot water cylinder do I need?

Cylinders typically come in sizes from 150litres up to 300litres. The size of hot water cylinder that you require will depend on the number of occupants in your home and your demand for hot water. For example, a family of four will have a larger hot water demand compared to a single occupancy home because they will use the taps, showers or bath more often. If you are researching a new heating system for your home, please speak to your installer who will be able to advise you about the most suitable size of cylinder you will need.

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Package Solutions

A heating system’s overall efficiency can be significantly improved by combining multiple technologies. From heat pumps to cylinders and effective heat emitters, you can get all of these products from Grant.

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