How Does an Air Source Heat Pump Work?

 

An air source heat pump takes low-temperature heat from the outside air and uses electricity to raise it to a temperature that can be used within the home.

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The principle is similar to the technology used in a refrigerator, but operating in reverse.

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Even when the outside air feels cold, it still contains heat energy that can be captured.

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A typical system uses an external unit containing a fan and refrigeration circuit. Heat collected outside is transferred into the property and used by the heating system.

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Because the heat pump is moving existing heat rather than generating all of the heat directly from electricity, it can deliver considerably more heat energy than the electrical energy it consumes.

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Air to Water Heat Pumps

 

An air to water heat pump transfers heat from the outside air into a water-based central-heating system.

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This is the type most commonly considered as an alternative to a conventional boiler.

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The heated water can supply:

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• radiators;

• underfloor heating;

• domestic hot water; and

• other suitable water-based heating systems.

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Air to water heat pumps normally operate at lower water temperatures than traditional gas boilers, which means the existing radiators, pipework and insulation of the property need to be considered carefully.

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Air to Air Heat Pumps

 

An air to air heat pump operates differently.

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Instead of heating water for radiators, the system transfers heat directly into the rooms through indoor fan units.

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Many air to air systems can also operate in reverse and provide air conditioning during warmer weather.

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This makes them particularly interesting for homeowners who want both heating and summer cooling.

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Air to air heat pumps are commonly used in:

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• extensions;

• open-plan living spaces;

• home offices;

• garden rooms;

• loft conversions; and

• properties where conventional wet central heating is less practical.

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They do not normally provide domestic hot water, so a separate hot-water system may still be required.

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Air Source Heating for UK Homes

 

Air source heating can be suitable for many different types of property, but the performance of the system depends heavily on the characteristics of the home.

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A modern well-insulated property may be relatively straightforward.

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An older period property with high heat loss may require improvements to the building fabric, larger radiators or other alterations before a heat pump can operate effectively.

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That does not automatically mean an older house cannot use a heat pump.

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It means that the whole property needs to be considered before the heating system is designed.

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Is My Home Suitable for an Air Source Heat Pump?

 

Suitability can depend on:

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• age and construction of the property;

• existing insulation;

• heat loss;

• existing radiators;

• underfloor heating;

• available external space;

• hot-water requirements;

• existing pipework;

• electrical supply;

• neighbouring properties;

• possible noise considerations; and

• planning constraints.

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A Green Home Survey can help establish whether a heat pump appears worth investigating and what other improvements may need to be considered alongside it.

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Insulation and Heat Pumps

 

Insulation can have an important effect on heat-pump performance.

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A property that loses heat quickly will require more energy to maintain a comfortable internal temperature.

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Improving roof, wall or floor insulation may reduce the amount of heat the property requires and potentially allow the heating system to operate more efficiently.

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This is why the first question should not always be:

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“Which heat pump should I buy?”

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It may be:

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“What should I do to the house before installing a heat pump?”

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For some homes, insulation improvements should form part of the project before or at the same time as the heating-system change.

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Heat Pumps and Radiators

 

One of the most common questions homeowners ask is whether their existing radiators can be retained.

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Sometimes they can.

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However, conventional boilers often supply water at higher temperatures than an air source heat pump.

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Because heat pumps generally operate more efficiently at lower flow temperatures, the heating system may require:

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• larger radiators;

• additional radiators;

• low-temperature radiators;

• fan-assisted emitters;

• underfloor heating; or

• improvements to the building fabric.

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A proper heat-loss assessment is normally required before the final heating-system design is established.

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Air Source Heat Pumps and Underfloor Heating

 

Underfloor heating can work particularly well with heat pumps because it uses a large surface area to distribute heat at relatively low water temperatures.

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This can make it attractive where major renovation, an extension or a new floor construction is already proposed.

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It does not mean that underfloor heating is essential.

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A properly designed radiator system can also operate successfully with a heat pump.

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The correct solution depends on the individual property.

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Air Source Heat Pump Installation

 

Air source heat pump installation involves considerably more than positioning an outdoor unit beside the house.

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Depending on the system, the work may include:

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• external heat-pump unit;

• internal controls;

• hot-water cylinder;

• buffer vessel;

• pumps and valves;

• pipework alterations;

• radiator changes;

• underfloor heating;

• electrical upgrades;

• new controls;

• condensate drainage; and

• commissioning.

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The existing heating system should be assessed before equipment is selected.

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Replacing a boiler with a heat pump without considering the wider system can result in poor performance and unnecessary running costs.

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Where Can an Air Source Heat Pump Be Installed?

 

The external unit requires a suitable location with enough space for airflow and maintenance access.

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Possible locations may include:

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• rear gardens;

• side passages;

• external walls;

• courtyards;

• flat roofs;

• garages or outbuilding areas; and

• other suitable external spaces.

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The position needs to take account of airflow, access, pipe runs, appearance, neighbouring properties and noise.

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The closest available space is not necessarily the best location.

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Air Source Heat Pump Noise

 

Modern air source heat pumps are designed to operate relatively quietly, but they do contain fans and compressors.

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Noise therefore needs to be considered when deciding where the external unit should be positioned.

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Potential issues include:

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• proximity to bedroom windows;

• neighbouring properties;

• narrow side passages;

• enclosed courtyards;

• hard surfaces that may reflect sound; and

• multiple heat-pump installations in close proximity.

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Good positioning can make a considerable difference.

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Air Source Heat Pump Cost

 

The cost of an air source heat pump can vary significantly from one property to another.

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The final price may be influenced by:

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• size and output of the heat pump;

• manufacturer;

• complexity of installation;

• hot-water cylinder requirements;

• radiator replacements;

• underfloor heating;

• pipework alterations;

• electrical upgrades;

• location of the external unit;

• access;

• controls; and

• other improvements required to the property.

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A straightforward installation into a suitable modern heating system may be considerably less complicated than converting a large older property with inadequate insulation and undersized radiators.

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The cost should therefore be considered as the cost of the complete heating-system upgrade, rather than simply the price of the outdoor heat-pump unit.

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How Much Does an Air Source Heat Pump Cost to Run?

 

Running costs depend on several variables, including:

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• heat demand of the property;

• insulation;

• system efficiency;

• flow temperature;

• electricity tariff;

• outdoor temperatures;

• hot-water use; and

• household heating habits.

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A properly designed heat-pump system operating in a suitable property can be very efficient.

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A poorly designed system working at unnecessarily high temperatures in a high heat-loss property may perform much less effectively.

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This is another reason why the property should be assessed before a heating-system decision is made.

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Air Source Heat Pumps and Solar Panels

 

Solar panels and heat pumps can complement one another because both move a property towards greater use of electricity.

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Solar PV can generate electricity that may contribute towards operating the heat pump.

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However, there is an important seasonal difference.

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Solar generation is greatest during spring and summer, while heating demand is highest during winter.

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Solar panels should therefore not be expected to provide all of the electricity required by a heat pump.

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They can nevertheless form a useful part of the wider home energy strategy.

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Heat Pumps and Battery Storage

 

Home battery storage may also work alongside a heat pump.

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A battery can store surplus solar electricity or electricity purchased during cheaper tariff periods and make it available later.

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The value of this arrangement depends on:

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• heat-pump electricity demand;

• solar generation;

• battery capacity;

• household electricity use;

• tariff structure; and

• the way the system is controlled.

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Where solar panels, battery storage and a heat pump are all being considered, it makes sense to assess the technologies together.

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Heat Pumps and Smart Energy Tariffs

 

The move from gas or oil heating to an electric heat pump changes the way a home consumes energy.

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Smart tariffs may provide opportunities to purchase electricity at lower prices during certain periods.

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Battery storage, thermal storage, hot-water cylinders and smart heating controls may allow some energy use to be shifted towards cheaper times.

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The increasing interaction between heating, electricity generation and storage is one of the reasons a whole-home energy strategy can be valuable.

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Air to Air Heat Pumps and Air Conditioning

 

Air to air heat pumps are particularly interesting because many systems can both heat and cool a property.

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During winter they operate as a heat pump, transferring heat from outside into the home.

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During summer the process can be reversed, allowing the same system to provide air conditioning.

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For properties experiencing increasing summer overheating, this can provide a useful alternative to installing completely separate heating and cooling systems.

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The additional summer electricity demand should also be considered alongside solar generation, as solar output is often strong at the same time that cooling is required.

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Do Air Source Heat Pumps Need Planning Permission?

 

Many domestic air source heat pump installations may be possible without making a full planning application, provided the relevant conditions and limitations are satisfied.

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However, planning considerations can become more important for:

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• listed buildings;

• conservation areas;

• flats and maisonettes;

• prominent locations;

• constrained sites;

• installations close to boundaries; and

• properties where several external units are proposed.

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Noise, visual impact and equipment location may also influence the planning position.

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Where there is uncertainty, it is sensible to establish the requirements before ordering equipment.

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Heat Pumps on Listed Buildings and in Conservation Areas

 

Older and historic properties can present additional challenges.

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An external heat-pump unit may affect the appearance or setting of the building, while changes to the internal heating system may interact with historic fabric.

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Possible locations should therefore be considered carefully.

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In some cases, a less prominent rear or side location may be preferable.

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Where a property is listed or lies within a sensitive conservation area, professional planning advice may be appropriate before installation proceeds.

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Air Source Heat Pumps During an Extension or Renovation

 

Major building work can provide an excellent opportunity to consider changing the heating system.

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An extension, loft conversion or whole-house refurbishment may already involve:

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• new insulation;

• new floors;

• replacement glazing;

• new radiators;

• underfloor heating;

• electrical upgrades; and

• changes to hot-water systems.

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Considering the heat pump at design stage can allow these elements to be coordinated rather than retrofitted later.

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It may also allow the heating system to be designed around the improved energy performance of the completed property rather than the house as it exists today.

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Air Source Heat Pump Grants and Funding

 

Financial support may sometimes be available towards qualifying heat-pump installations.

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Grant schemes, eligibility requirements and funding levels can change, so homeowners should check the current position before making decisions based on a particular level of support.

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Funding can improve the financial case for a heat pump, but the suitability and design of the system should remain the starting point.

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Air Source Heat Pumps Versus Gas Boilers

 

A heat pump operates differently from a traditional gas boiler.

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A boiler typically produces relatively high-temperature water and may run for shorter periods.

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A heat pump generally performs most efficiently when providing lower-temperature heat over longer periods.

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This means homeowners may notice a different style of heating operation.

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The objective is usually to maintain a comfortable and relatively consistent indoor temperature rather than repeatedly allowing the property to cool and then reheating it quickly.

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Air Source Heat Pumps Versus Air Conditioning

 

The distinction depends largely on the type of heat pump.

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An air to water heat pump normally supplies water to radiators, underfloor heating and hot-water systems.

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An air to air heat pump supplies conditioned air directly to rooms and can often provide both heating and cooling.

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For some homes, one system may be clearly more appropriate.

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For others, a combination could be considered.

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Is an Air Source Heat Pump Worth It?

 

There is no universal answer.

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An air source heat pump may be an excellent investment for one property and a poor priority for another.

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Before deciding, it is worth understanding:

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• how much heat the home requires;

• existing insulation;

• radiator suitability;

• hot-water requirements;

• available external space;

• likely installation cost;

• electricity demand;

• possible grant support;

• future solar plans; and

• whether other improvements should come first.

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The important thing is to assess the whole home rather than buying the technology in isolation.

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Independent Heat Pump Advice

 

Heat-pump installers naturally concentrate on supplying and installing heating systems.

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APN Green Homes takes a broader approach.

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A Green Home Survey can consider the heat pump alongside insulation, glazing, solar panels, battery storage, ventilation, EV charging and other planned improvements.

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This can help establish whether a heat pump appears appropriate, whether the property should be improved first and how the heating change fits into the longer-term energy strategy for the home.

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Start With the Property

 

The best heat pump installation begins with understanding the building.

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Before replacing a boiler or choosing equipment, it makes sense to understand the home's heat loss, existing heating system, insulation, future energy requirements and the other improvements you may be considering.

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NEXT STEPS

Every home is different, so the right next step depends on your property, your budget and what you want to achieve. APN Green Homes can help you turn the information you have just read into a practical plan for your own home. Whether you are considering one improvement or looking at a complete whole-home energy upgrade, we can help you understand what is suitable, what should be prioritised and where your money is likely to make the greatest difference.

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Choose one of the options below to get the ball rolling:

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BOOK A GREEN HOME SURVEY
Get a detailed assessment of your home with practical, property-specific recommendations and a clear plan for the improvements worth considering.

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BOOK A PHONE CONSULTATION
Talk through your property, ideas and priorities with us and get some initial direction on the best way forward.

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EMAIL US
Send us details of your property, photographs or any questions and we can advise you on the most appropriate next step.

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GIVE US A CALL
Prefer to speak to someone? Give us a call and tell us what you are hoping to achieve.

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Your greener, more efficient home starts with understanding the right improvements for your property — and putting them in the right order.