Air source heat pump installation in Hertfordshire

What does installing an air source heat pump involve?

An air source heat pump takes heat from the outside air and uses it to warm water for your radiators, underfloor heating and taps. The main parts are an outdoor unit, pipework running through a wall into the house, a hot water cylinder, and controls. It is a bigger job than swapping one boiler for another, because the whole heating system is affected.

Why does a heat loss survey come first?

A heat pump should be sized to the home it serves. The installer works out how much heat each room loses on a cold day, using the size of the rooms, the walls, windows, roof and floors, and how well air-tight the house is. That calculation sets the output the pump needs and shows which radiators will cope.

Be wary of anyone who proposes a model without one. A pump that is too small struggles on cold days, and one that is too large tends to cycle on and off.

Will my existing radiators be enough?

A heat pump works best when it delivers heat at a lower water temperature than a boiler does. To give the same warmth at that lower temperature, radiators need more surface area. Some rooms get by with what they have, some need larger or double-panel radiators, and some are better served by underfloor heating or fan-assisted units.

The heat loss survey should list this room by room. Pipework matters as well. Old narrow pipes may restrict flow, and the installer may suggest replacing sections.

What happens to the hot water?

Most heat pumps heat water for the taps by storing it in a cylinder. If your home has a combination boiler and no tank, you will need space for one, often in an airing cupboard, a utility room or a loft. Ask the installer what size they propose and where it will go.

Unvented cylinders are pressurised and are covered by Building Regulations, so ask how the fitting will be certified. A cylinder with a built-in immersion heater can also provide a backup.

Where can the outdoor unit go?

The unit needs clear airflow around it, solid ground or a wall bracket, and a short, tidy run to the house. Think about:

• windows of your own bedrooms and your neighbours' rooms nearby
• the boundary with the next property
• access for servicing, and space for condensation to drain away
• snow, leaves and anything that could block the air flow

In England, fitting an air source heat pump to a house can sometimes be done as permitted development, without applying for planning permission, but only when a list of conditions is met. The conditions cover things such as the position of the unit, its size and noise. They can differ for flats and for homes in a conservation area, and the rules have been changing, so ask the installer to confirm the position against the current national rules and your council's guidance. Permitted development does not apply to a listed building or to land within its curtilage, so a listed home needs a planning application, and usually listed building consent as well.

How loud is a heat pump?

All of them make some noise, mostly a fan and a low hum from the compressor. Noise carries differently around a garden, so the position of the unit counts for more than the model alone. Noise is also part of the permitted development conditions, so ask for the installer's assessment of your chosen spot, and think about how it will sound from a neighbour's window as well as from yours.

Why does MCS certification matter?

MCS, the Microgeneration Certification Scheme, sets standards for small-scale renewable installations and certifies installers and products. In England and Wales, the Boiler Upgrade Scheme, a government grant towards a heat pump, requires the work to be done by an MCS certified installer using a product that meets MCS standards, and the installer makes the application. Support rules change, so check the current Boiler Upgrade Scheme on gov.uk before you commit to anything, and ask any installer for their MCS certificate number and check it on the MCS installer search.

What else might the job involve?

• an electrical supply that is large enough, and sometimes a new circuit or consumer unit
• new controls and a way to balance the system
• insulation advice, because a warmer home needs a smaller pump
• Building Regulations compliance for the heating work and the cylinder

What should I include when I enquire?

• your postcode, and whether the home is a house, bungalow or flat
• roughly when it was built and what you use for heating now
• whether there is a hot water tank already
• where a unit could stand: side passage, garden, flat roof or wall
• whether the property is listed or in a conservation area