Air source heat pumps have gone from a niche technology to one of the most talked-about home heating solutions in the UK. With the government pushing hard to phase out gas boilers in new builds and offering generous grants to help homeowners make the switch, more people across Cornwall and Devon are asking whether an ASHP could work for their property. In this guide, we break down how they work, what they cost, and whether they make financial sense for you.
How Does an Air Source Heat Pump Work?
An air source heat pump works on the same principle as a refrigerator, but in reverse. Instead of extracting heat from inside a fridge and releasing it into the room, an ASHP extracts heat from the outside air and uses it to warm your home and hot water.
The system consists of an outdoor unit (which looks similar to an air conditioning unit) and an indoor unit connected to your central heating system. The outdoor unit contains a fan that draws in air, and a refrigerant that absorbs heat from that air even when temperatures are as low as minus 15 degrees Celsius. The refrigerant is then compressed, which raises its temperature significantly, and this heat is transferred to your heating circuit via a heat exchanger.
For every unit of electricity the heat pump uses to run, it typically produces between 2.5 and 3.5 units of heat. This ratio is known as the Coefficient of Performance (CoP), and it means an ASHP is two to three times more efficient than a traditional electric heater. In the relatively mild climate of Cornwall and Devon, where winter temperatures rarely drop below freezing for extended periods, air source heat pumps perform particularly well.
What Does It Cost to Install?
The total cost of installing an air source heat pump in a typical three to four bedroom house ranges from around 8,000 to 14,000 pounds, depending on the size of the system, the brand, and how much work is needed to integrate it with your existing heating infrastructure.
The main cost factors include the heat pump unit itself (3,000 to 7,000 pounds), installation labour (2,000 to 4,000 pounds), any upgrades to your radiators or underfloor heating (if needed), a hot water cylinder (ASHPs do not work with combi systems — you need a cylinder), and any changes to the electrical supply such as upgrading to a three-phase connection for larger units.
If your property already has underfloor heating or oversized radiators, the integration costs will be lower because the system can run at a lower flow temperature, which is where heat pumps are most efficient. If you have standard panel radiators, some or all of them may need to be upsized to compensate for the lower water temperature compared to a gas boiler.
The Boiler Upgrade Scheme (BUS Grant)
The UK government's Boiler Upgrade Scheme, launched in April 2022 and extended through to 2028, offers a grant of 7,500 pounds towards the cost of installing an air source heat pump in an existing property. This is a significant contribution that brings the net cost of many installations down to between 2,000 and 6,000 pounds — comparable to, or even less than, a new gas boiler installation.
To qualify for the BUS grant, your property must be in England or Wales, you must own the property (it does not apply to new builds), your home must have an EPC (Energy Performance Certificate) with no outstanding recommendations for loft or cavity wall insulation (unless there is a valid reason they cannot be installed), and the installation must be carried out by an MCS-certified installer.
Tip: The BUS grant is applied at the point of installation — you do not need to pay the full amount and claim it back. Your installer applies for the voucher on your behalf, and the grant is deducted from your invoice. This makes the process straightforward and removes the need to fund the full cost upfront.
Is Your Property Suitable?
Air source heat pumps work well in a wide range of properties, but some are better suited than others. The ideal candidate is a well-insulated detached or semi-detached house with space for the outdoor unit, a hot water cylinder, and either underfloor heating or radiators that can be upgraded if necessary.
Properties with solid walls (common in older Cornish and Devon cottages) may need external or internal wall insulation before an ASHP will perform efficiently. This is because the heat pump operates at a lower flow temperature than a gas boiler, so the property needs to retain heat well for the system to maintain comfortable temperatures without running constantly.
Terraced houses and flats can also have heat pumps installed, but there are additional considerations around noise (the outdoor unit produces a low hum, similar to a fridge), planning permission in conservation areas, and available outdoor space. For listed buildings, which are common across the South West, you will need to check with your local conservation officer before proceeding.
The good news is that planning permission is not usually required for domestic ASHPs, as they fall under permitted development rights in most cases. However, there are conditions — the unit must comply with noise limits measured at the nearest neighbour's window, and there are restrictions on the number and placement of outdoor units.
Running Costs: Heat Pump vs Gas Boiler
This is the question everyone asks, and the answer depends on several factors including your electricity tariff, the efficiency of the heat pump, and how well insulated your property is.
As a general guide, a well-installed ASHP with a CoP of 3.0 will use around one unit of electricity for every three units of heat it produces. At current electricity prices of roughly 24.5 pence per kWh, that works out to an effective heating cost of about 8.2 pence per kWh of heat. A gas boiler running at 90 percent efficiency, with gas at around 6.2 pence per kWh, produces heat at an effective cost of about 6.9 pence per kWh.
On paper, gas is still slightly cheaper per unit of heat. However, the gap narrows significantly if you are on a time-of-use electricity tariff (where you can run the heat pump during off-peak hours at lower rates), if you have solar panels generating some of your own electricity, or if the government adjusts the balance of green levies between gas and electricity, which is currently under review.
For properties that are currently on oil, LPG, or electric storage heating — which is common in rural parts of Cornwall and Devon where mains gas is not available — an air source heat pump will almost certainly reduce your heating bills significantly. Oil currently costs around 8 to 10 pence per kWh of heat, and LPG around 10 to 12 pence, so the savings can be substantial.
Important: If your property is off the gas grid and you are currently heating with oil or LPG, an air source heat pump is one of the strongest financial cases for switching. Combined with the BUS grant, you could recoup your investment within four to six years through lower running costs alone.
What Does the Installation Process Involve?
A typical ASHP installation takes between two and five days, depending on the complexity of the project. The process begins with a detailed survey of your property by an MCS-certified installer, who will assess your heat loss, check your existing heating system, and design the right size of heat pump for your needs.
On installation day, the outdoor unit is positioned on a concrete pad or wall brackets, refrigerant pipework is run between the outdoor and indoor units, the indoor unit and hot water cylinder are installed, the system is connected to your existing heating circuit, and all controls, thermostats, and programming are set up.
Once installed, the system is commissioned and tested to make sure it is running at the correct pressures and temperatures. Your installer will walk you through the controls and explain how to get the best performance from the system. Most modern ASHPs come with a smartphone app that lets you monitor energy use, adjust temperatures, and set schedules remotely.
Get a Heat Pump Quote from NJG
At NJG Construction, we work with MCS-certified heat pump installers across Cornwall and Devon. Whether you are replacing an old oil boiler in a rural cottage or upgrading a modern home, we can arrange a full property survey, provide a detailed quote, and handle the BUS grant application on your behalf.
The first step is a no-obligation assessment of your property. Raise a job online or call us on 07915 357552 to get started.
