Heat Pump Installation: What Actually Happens

Most people considering a heat pump have read about running costs and grants, and almost nothing about the week itself. How much of the house gets pulled apart? Will there be heating that night? What are three people doing in the airing cupboard for two days?

A typical air source heat pump install takes 2 to 3 days. Here is what fills them.

Before anyone turns up

The survey does the real work. A room by room heat loss calculation sets the size of the heat pump, the flow temperature the system will run at, and which radiators, if any, need changing. That calculation is also what the design is signed off against, so it has to happen before a van is booked, not after.

Two bits of paperwork run in the background. Your distribution network operator is notified about the new electrical load, which is routine and handled for you. And the Boiler Upgrade Scheme application goes in, which needs a valid EPC with no outstanding insulation recommendations. The grant is £7,500 for an air source heat pump, or £9,000 if you are off the gas grid on oil or LPG, and it is claimed on your behalf so it comes off the price rather than arriving months later.

Day one: the old system comes out

The heating gets drained down first, so expect the house to be cold for a good part of the first day. In winter we plan the sequence so you are not without hot water overnight.

Outside, the unit goes on a level base or wall brackets, usually against a side or rear wall with clearance for airflow, and a condensate run is set up to drain safely. Inside, the old boiler comes off the wall and the flue hole is made good. If a gas boiler is being replaced, the gas supply to it is capped off properly by someone qualified to do it.

Day one and two: the new system goes in

The indoor side is the bigger job. A heat pump needs a hot water cylinder, because it heats water more gently than a boiler does and cannot fire up on demand in the same way. That cylinder usually lives where the old one did, or in the airing cupboard, loft or garage, and it is the single biggest space requirement in the house.

Then there is pipework between the outdoor unit and the cylinder, often the fiddliest part of the week in an older property, plus any radiator swaps the survey called for and a dedicated electrical circuit from the consumer unit. Floorboards may come up. In most homes the disruption is concentrated in one or two rooms and the route the pipes take.

Commissioning is the part that decides your bills

This is where installs quietly succeed or fail. The system is flushed and dosed with inhibitor, which matters enormously in an older house full of sludge. Radiators are balanced so every room reaches temperature at the same rate. The flow temperature is set as low as the heat loss figures allow, and weather compensation is configured so the system raises and lowers that temperature with the outside air rather than running flat out all winter.

Seasonal efficiency (SCOP) of 2.5 to 4 is the realistic range, and commissioning is most of what decides where in that range you land. A well specified heat pump set up badly will cost you money for years.

Handover and the paperwork

Before the job is signed off you should get a walkthrough of the controls, including how to set the heating schedule and the hot water times, and an explanation of why you leave it running steadily rather than blasting it twice a day.

You then receive the MCS certificate, which is what proves the install meets the standard and underpins the grant, plus manufacturer warranty registration. Grant Store Ltd is MCS accredited and RECC registered, and we manage the job and take responsibility for it from survey to handover.

What can add a day

Cylinder space that needs reworking, microbore pipework that restricts flow, a consumer unit that needs upgrading, or genuinely foul weather while the outdoor unit goes in. A proper survey flags all of these in advance, which is the main reason we would rather spend an hour in your loft before quoting than discover it on day two.

Heat pumps start from around £3,000 after the grant. If you would like someone to look at the house, work out the heat loss and tell you honestly what your install would involve, our survey is free and there is no obligation.