Air source heat pumps are becoming increasingly popular in UK homes as homeowners look for alternatives to traditional gas and oil boilers. But how do they actually work, and are they worth considering for your home?
What is an air source heat pump?
An air source heat pump takes heat energy from the outside air and transfers it into your home's heating system. An air-to-water heat pump transfers this heat into water, which can then be used to heat radiators, underfloor heating and a hot water cylinder.
Unlike a conventional boiler, the system does not burn gas or oil to produce heat. Instead, it uses electricity to operate the heat pump.
How does it work?
The basic process is:
Even when the outside temperature is low, there is still heat energy in the air. The heat pump extracts this energy and raises its temperature so that it can be used inside your home. A compressor and refrigerant circuit are used to transfer and increase the temperature of the heat energy.
Does a heat pump use electricity?
However, heat pumps are designed to produce more heat energy than the electrical energy they consume. Energy Saving Trust explains that a heat pump can produce around three units of heat for each unit of electricity under suitable conditions.
Actual performance depends on the system design, outdoor temperature, flow temperature, controls and how the system is operated.
Will my existing radiators work?
A heat pump normally operates at a lower flow temperature than a traditional boiler. This means the radiators may need to be larger or upgraded in some rooms. This is why a proper heat-loss calculation and system design are important before installation.
Your installer should assess the existing radiators and determine whether they can provide enough heat at the proposed operating temperature.
What about hot water?
An air-to-water heat pump can also heat domestic hot water.
Unlike a typical combi boiler, a heat pump system will normally use a hot water cylinder to store heated water for showers, baths and taps. The installer will assess the property's hot water requirements and recommend an appropriate cylinder size.
What are the benefits?
A properly designed air source heat pump can offer several benefits:
- Uses renewable heat from the outdoor air.
- Can reduce reliance on fossil fuels.
- Can provide both heating and hot water.
- Can work with radiators or underfloor heating.
- Can reduce carbon emissions compared with many conventional heating systems.
- May reduce running costs depending on the system being replaced and electricity tariff.
Savings are not guaranteed and depend heavily on the property and system design.
Are heat pumps expensive to run?
Running costs depend on:
- Your home's heat loss.
- The efficiency of the heat pump.
- Radiator sizing.
- Flow temperature.
- Electricity tariff.
- How you use the heating system.
- The system being replaced.
A heat pump that has been correctly designed and commissioned can operate efficiently, but homeowners should not rely solely on the headline efficiency figure. Seasonal performance is a better indication of how a system performs across the year.
Are air source heat pumps worth it?
For many homeowners, they can be.
However, the right question is not simply "Is a heat pump worth it?" but "Is a heat pump properly designed for my property?"
A professional survey should establish the property's heat requirement and identify any required radiator, cylinder, electrical or other upgrades. The Boiler Upgrade Scheme can also significantly reduce the upfront cost for eligible properties.
