An air source heat pump, also known as an air-to-water source heat pump, uses captured heat from the air outside your home to heat your central heating system and heat the water in a hot water cylinder feeding to all of your hot taps and showers.

Heat from the air is absorbed into a fluid. This fluid then passes through a heat exchanger into the heat pump, which raises the temperature and then transfers that heat to water. An  air source heat pump works on the same concept as a ground source heat pump but with its own set of advantages and disadvantages. A heat pump will deliver the heat at a lower temperature than a gas boiler, so they will need to be run for longer, but they are more energy efficient than operating a gas boiler.

Does my home have space for an air source heat pump?

Unlike a ground source heat pump, a house does not need a lot of outside space for an air source heat pump to be fitted. For the air-to-water source heat pump unit to work, there needs to be space to install the unit outside against an exterior wall with free space around the unit for good airflow.

The outdoor unit of an air source heat pump contains the important fan component. This is what draws in the air that is turned to heat your home and hot water.

There are different types of air source heat pumps;

• single large units called Monobloc pumps
• two part units, (an outdoor and an indoor unit), called Split pumps - the benefit of Split pumps is some fan units can be placed a distance away from the house to avoid the noise of the air heat pump.

This means if you live in a mid-terrace home, an air source heat pump will be an available option for you as long as there is patio or garden space to fit the unit. Unlike installing a ground source heat pump where there is not enough outdoor space for one to be dug in.

Which is better, an air or ground source heat pump?

Both heat pumps come with their own set of benefits but the biggest benefit of an air source heat pump is that fitting them is more cost effective than ground source heat pumps, and they need less outdoor space to be installed.

Both heat pumps  are low-maintenance with less CO2 emissions emitted than gas boilers. An air source heat pump is noisier than the ground source heat pump but more than half of the UK homes do not have the outdoor space for trenches or boreholes to be dug. Or for digger machinery to access the garden making them non-viable for a ground source heat pump and leaving the only option of a heat pump to be an air source heat pump installed along an exterior wall, making no difference if it is a front, side or back wall as long as there is air flow around.

How much will it cost to install an air source heat pump?

The cost to install an air source heat pump is significantly less than installing a ground source heat pump. The prices for supplying and installing is more like £8,000 to £15,000 as opposed to a ground source heat pump that can reach £45,000.

The Boiler Upgrade Scheme (BUS grant) is £5,000 towards the cost of the installation of the air source heat pump and because they are energy efficient, the savings you make begin from the day you start using the new heat pump.

The installation time for the gas engineer, is anywhere from 1-3 days of labour. Labour makes up only 10% of the cost with the bulk of the expense being the materials for the air source heat pump.

A budget unit costing £7500 to install will be £6750 materials and only £750 labour cost for the engineer.

Cost to install an air source heat pump	Per	Average total labour cost
Installing a monobloc pump	Per day	£550
Installing a split pump	Per day	£750
Installing the hot water cylinder	Per day	£300
Replacing a component on the heat pump, e.g.; evaporator, compressor, condenser or an expansion valve	Per hour	£180

Is an air source heat pump better than a gas boiler?

The initial installation cost of a gas boiler is far cheaper, but then there are more on-going maintenance charges and components can be very delicate, needing more parts changed over the years than an air source heat pump as well as the gas boiler needing annual gas checks.

The air source heat pump typically outputs 3x more heat for every unit of energy it uses to capture heat from the air, this makes the heat pump 300% more energy efficient.

They are a low carbon heat source. A well designed and installed air source heat pump can be overall cheaper to run than a gas boiler, which in time will make up for the higher initial installation cost.

What are the advantages of an air source heat pump?

Air source heat pumps do have many advantages including;

• a very energy efficient system
• the UK has government grants to help towards the cost of installing an air source heat pump
• unlike a ground source heat pump, the air source can be installed with minimum disruption to your outdoor space
• they require low-maintenance
• their lifespan is a lot longer than gas boilers
• some units can provide a cooling summer function

Some of the main downsides to an air source heat pump is that they are noisy, need outside space to have the unit fixed to a wall, radiators will be warm but never very hot to touch and the upfront cost is a lot more than a gas boiler.

Estimates for common heating engineer jobs;

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