Guide · Updated 8 November 2026
Air to air heat pump installation
A single-room air to air heat pump is usually installed in one day; a multi-room system in two to three. The installer mounts an indoor unit high on a wall in each room, an outdoor unit outside, and links them with a small refrigerant pipe through a hole about 65mm wide. Anyone handling the refrigerant must hold F-gas certification, and for the £2,500 grant the installer must also be MCS certified for air to air.
Before the day: the survey
A proper installer visits or does a video survey before quoting. They should work out how much heat each room needs (a heat loss calculation), not just match a unit to the room size. This matters more for an air to air heat pump than for air conditioning, because in winter it has to keep the room warm on the coldest days, not just take the edge off a summer afternoon.
Expect them to check:
- where each indoor unit can go (high on a wall with clear airflow, usually opposite or beside a window)
- where the outdoor unit can sit: a wall bracket or ground pad with space around it for airflow, and away from neighbours' windows to keep within noise limits
- the pipe route between the two, and how the condensate (water) will drain away
- your consumer unit, because the system needs its own electrical circuit
- whether you need permission: planning, listed building consent, or your freeholder if you own a flat on a lease
On the day
- Indoor unit. A mounting plate is fixed to the wall and a hole is drilled through to the outside for the pipes, cable and drain.
- Outdoor unit. Fitted on brackets or a pad. Anti-vibration feet help keep noise down.
- Pipework. Two insulated copper refrigerant pipes, a control cable and a condensate drain run between the units, usually inside white trunking on the outside wall.
- Electrics. A new circuit from your consumer unit. This is notifiable work under Part P of the Building Regulations (in England and Wales), so the electrician should give you a certificate.
- Pressure test and vacuum. The installer tests the pipework for leaks, pulls a vacuum to remove air and moisture, then releases the refrigerant. This is the step that legally needs F-gas certification.
- Commissioning and handover. They should run the system in heating mode, show you the controls and app, and give you the paperwork.
How long it takes
| System | Typical time on site |
|---|---|
| One room (single split) | About a day |
| Two to four rooms (multi-split) | Two to three days |
| Ducted (hidden in a loft or ceiling void) | Three days or more |
Certifications your installer needs
- F-gas certification for the engineers, and company F-gas certification for the business (for example through REFCOM, Quidos or BESCA). This is a legal requirement for anyone handling the refrigerant, grant or no grant.
- MCS certification for air to air heat pumps if you want the £2,500 Boiler Upgrade Scheme grant. Air to air has its own MCS standard (MCS 031 b), introduced in 2026, so an installer who is MCS certified for air-to-water heat pumps is not automatically certified for air to air. Ask.
- Part P electrical sign-off for the new circuit, either from their own electrician or a registered contractor.
What it costs
The government's own figure is about £4,500 for a flat or small house, before the £2,500 grant. One room is cheaper and a whole larger house is more. See our air to air heat pump cost guide for a full breakdown.
What to ask before you book
- Is your business F-gas certified, and is it MCS certified for air to air (MCS 031 b)?
- Did you work out the heat loss of each room?
- Where exactly will the outdoor unit go, and will it meet the 42 dB limit at the neighbour's window?
- Does the price include the electrical work, trunking, condensate pump (if needed) and making good?
- Will you apply for the grant and take it off the quote?
- What warranty comes with the equipment and the workmanship, and how often does it need servicing?
Questions
How long does an air to air heat pump installation take?
One room usually takes about a day. A multi-split system covering two to four rooms usually takes two to three days, and a ducted system longer.
Do I need planning permission?
Often not. In England, units that provide heating and meet MCS 020 noise and siting rules are usually permitted development. Flats, listed buildings and conservation areas have extra limits. See our planning permission guide.
Can any air conditioning engineer fit one?
They need F-gas certification to handle the refrigerant. To get the £2,500 grant, the installer must also be MCS certified for air to air heat pumps, which is a newer and separate certification.
Is it messy?
Less than most heating work. The main jobs are drilling one hole per indoor unit, fixing trunking outside and running a new electrical circuit. There are no radiators or floors to lift.
Sources
- MCS: Update on the implementation of air-to-air heat pumps into MCS (13 Apr 2026)
- GOV.UK: Discounts for families to keep warm in winter and cool in summer (18 Nov 2025)
- GOV.UK: F gas in refrigeration, air conditioning and fire protection systems
- MCS: New permitted development rules in England, MCS 020(a)
Checked 8 November 2026.