A split system heat pump is an air-to-water heat pump in two parts: an outdoor unit that collects heat from the air, and an indoor unit called a hydrobox where that heat is passed into the water for your heating and hot water. The two are connected by insulated refrigerant pipes rather than water pipes, so there is no water outside to freeze.
Installers covering Greater London keep refrigerant routes neat and protected along the outside wall. Owners across Greater London can compare split and monobloc designs side by side at a survey in Greater London. Flats and terraces in Greater London with a small yard or flat roof can suit a compact split outdoor unit.
Who it suits
- Homes where the outdoor unit must sit some distance from the plant space
- Owners who would rather not use glycol or anti-freeze valves
- Exposed or frost-prone sites where outdoor water pipes would be a risk
- Small yards, roofs or balconies that suit a more compact outdoor unit
Grants and rules for heat pumps in England
In England the Boiler Upgrade Scheme gives £7,500 towards an air source heat pump (£9,000 if it replaces oil or LPG, from 21 July 2026 to 31 March 2027), and since 28 April 2026 a valid EPC is no longer needed. The grant is applied for by the MCS-certified installer and shown as a deduction on your quote.
Installing heat pumps is zero-rated for VAT across the UK until 31 March 2027. Since 29 May 2025, permitted development in England allows up to two air source heat pumps on a house, each up to 1.5 m³, with no blanket 1 m boundary rule — the installation must still meet the MCS planning standards, including the noise check. Listed buildings, flats and some conservation-area positions need extra consent, which we check at survey.
Split system heat pumps prices in Greater London
The ranges below are typical installed prices for homes in Greater London, including VAT. A survey sets the exact figure, because two similar-looking houses in Greater London can need quite different radiators and pipework.
| Home | Typical size | Installed guide price | After £7,500 grant |
|---|---|---|---|
| 1–2 bedroom flat or small terrace | 4–5 kW | £10,650–£14,000 | £3,150–£6,500 |
| 2–3 bedroom terrace or semi | 5–7 kW | £11,750–£15,100 | £4,250–£7,600 |
| 3 bedroom semi or small detached | 6–9 kW | £13,450–£17,350 | £5,950–£9,850 |
| 4 bedroom detached | 8–12 kW | £15,700–£20,150 | £8,200–£12,650 |
| 5+ bedroom or larger older house | 11–16 kW | £18,500–£25,200 | £11,000–£17,700 |
Installed, inc VAT: unit, cylinder, controls, minor pipework and commissioning.
Towns we cover in Greater London
We cover 90 towns in Greater London for split system heat pumps. Each links to local guide prices and the grant position for England.
| Town | Postcode district | Nearest town | Midwinter daylight |
|---|---|---|---|
| Islington | N1 | Highbury | 7 h 49 min |
| Bexley | DA5 | Bexleyheath | 7 h 50 min |
| Barking | IG11 | Ilford | 7 h 49 min |
| Sutton | SM1 | Carshalton | 7 h 51 min |
| Croydon | CR0 | Purley | 7 h 51 min |
| Ilford | IG1 | Barking | 7 h 49 min |
| Harrow | HA1 | Pinner | 7 h 49 min |
| Tottenham | N17 | Wood Green | 7 h 49 min |
| Walthamstow | E17 | Leyton | 7 h 49 min |
| Dagenham | RM10 | Barking | 7 h 49 min |
| Romford | RM1 | Hornchurch | 7 h 49 min |
| Hayes | UB3 | Southall | 7 h 49 min |
| Wembley | HA9 | Hendon | 7 h 49 min |
| Fulham | SW6 | Putney | 7 h 50 min |
| Southall | UB1 | Hayes | 7 h 49 min |
| Putney | SW15 | Fulham | 7 h 50 min |
| Battersea | SW11 | Chelsea | 7 h 50 min |
| Purley | CR8 | Coulsdon | 7 h 51 min |
| Peckham | SE15 | Dulwich | 7 h 50 min |
| Chingford | E4 | Woodford Green | 7 h 48 min |
| Uxbridge | UB8 | Ruislip | 7 h 49 min |
| Wimbledon | SW19 | Morden | 7 h 50 min |
| Brixton | SW2 | Clapham | 7 h 50 min |
| Hounslow | TW3 | Twickenham | 7 h 50 min |
| Finchley | N3 | Hendon | 7 h 49 min |
| Mitcham | CR4 | Morden | 7 h 51 min |
| Feltham | TW13 | Hounslow | 7 h 50 min |
| Acton | W3 | Chiswick | 7 h 49 min |
| Beckenham | BR3 | Bromley | 7 h 50 min |
| Chelsea | SW3 | Battersea | 7 h 50 min |
| Streatham | SW16 | Balham | 7 h 50 min |
| Eltham | SE9 | Blackheath | 7 h 50 min |
| Morden | SM4 | Mitcham | 7 h 51 min |
| Carshalton | SM5 | Sutton | 7 h 51 min |
| Catford | SE6 | Lewisham | 7 h 50 min |
| Surbiton | KT6 | Kingston upon Thames | 7 h 51 min |
| Stratford | E15 | Leyton | 7 h 49 min |
| Chiswick | W4 | Acton | 7 h 50 min |
| Ruislip | HA4 | Pinner | 7 h 49 min |
| Greenwich | SE10 | Blackheath | 7 h 50 min |
| Barnet | EN5 | Mill Hill | 7 h 48 min |
| Wood Green | N22 | Crouch End | 7 h 49 min |
| Muswell Hill | N10 | Crouch End | 7 h 49 min |
| Highbury | N5 | Islington | 7 h 49 min |
| Coulsdon | CR5 | Purley | 7 h 51 min |
| Hornchurch | RM11 | Upminster | 7 h 49 min |
| Blackheath | SE3 | Lewisham | 7 h 50 min |
| New Malden | KT3 | Kingston upon Thames | 7 h 51 min |
| Woodford Green | IG8 | Chingford | 7 h 48 min |
| Richmond | TW9 | Twickenham | 7 h 50 min |
| Barnes | SW13 | Putney | 7 h 50 min |
| Notting Hill | W11 | Kensington | 7 h 49 min |
| Pinner | HA5 | Harrow | 7 h 49 min |
| Golders Green | NW11 | Hampstead | 7 h 49 min |
| Tooting | SW17 | Balham | 7 h 50 min |
| Chislehurst | BR7 | Sidcup | 7 h 50 min |
| Orpington | BR6 | Chislehurst | 7 h 51 min |
| Balham | SW12 | Tooting | 7 h 50 min |
| Bexleyheath | DA6 | Bexley | 7 h 50 min |
| Bromley | BR1 | Beckenham | 7 h 51 min |
| Camden | NW1 | Kentish Town | 7 h 49 min |
| Clapham | SW4 | Brixton | 7 h 50 min |
| Crouch End | N8 | Highgate | 7 h 49 min |
| Dulwich | SE21 | Brixton | 7 h 50 min |
| Ealing | W5 | Acton | 7 h 49 min |
| Edgware | HA8 | Mill Hill | 7 h 48 min |
| Enfield | EN1 | Southgate | 7 h 48 min |
| Forest Hill | SE23 | Sydenham | 7 h 50 min |
| Hackney | E8 | Stoke Newington | 7 h 49 min |
| Hammersmith | W6 | Notting Hill | 7 h 50 min |
| Hampstead | NW3 | West Hampstead | 7 h 49 min |
| Hendon | NW4 | Golders Green | 7 h 49 min |
| Highgate | N6 | Crouch End | 7 h 49 min |
| Kensington | W8 | Notting Hill | 7 h 50 min |
| Kentish Town | NW5 | Camden | 7 h 49 min |
| Kingston upon Thames | KT1 | Surbiton | 7 h 50 min |
| Lewisham | SE13 | Blackheath | 7 h 50 min |
| Leyton | E10 | Walthamstow | 7 h 49 min |
| Mill Hill | NW7 | Edgware | 7 h 48 min |
| Sidcup | DA14 | Chislehurst | 7 h 50 min |
| Southgate | N14 | Enfield | 7 h 48 min |
| Stoke Newington | N16 | Highbury | 7 h 49 min |
| Sydenham | SE26 | Forest Hill | 7 h 50 min |
| Teddington | TW11 | Twickenham | 7 h 50 min |
| Twickenham | TW1 | Teddington | 7 h 50 min |
| Upminster | RM14 | Hornchurch | 7 h 49 min |
| Wandsworth | SW18 | Putney | 7 h 50 min |
| Wanstead | E11 | Leyton | 7 h 49 min |
| West Hampstead | NW6 | Hampstead | 7 h 49 min |
| Woolwich | SE18 | Eltham | 7 h 50 min |
Split system heat pumps questions
How big is a hydrobox?
A hydrobox is typically about the size of a wall-mounted boiler, though sizes vary by make and model. It needs wall space near the cylinder with room around it for servicing and pipe connections. Some manufacturers combine the hydrobox and cylinder in a single floor-standing unit similar in size to a tall fridge-freezer, which can suit a utility room or garage.
Is a split system eligible for the Boiler Upgrade Scheme?
Yes. A split air-to-water heat pump counts as an air source heat pump under the scheme, so in England and Wales eligible owners of existing homes can receive £7,500, or £9,000 when replacing oil or LPG within the published dates. The MCS-certified installer applies for you. Scotland's Home Energy Scotland funding is separate, and Northern Ireland has no dedicated homeowner grant at present.
Can a split system replace my combi boiler?
Yes, but like any air-to-water heat pump it needs a hot water cylinder, because it does not heat water instantly. The hydrobox can sometimes go where the combi was, with the cylinder in a cupboard, utility room or garage. Integrated units combining both are useful where one larger space is available. The survey checks what fits before the design is finalised.
How far apart can the outdoor unit and hydrobox be?
It depends on the model: each manufacturer sets a maximum refrigerant pipe length and height difference, and longer runs may need extra refrigerant. In practice a split system allows more flexibility than a monobloc's water pipes, so the outdoor unit can often sit on the far side of a house, on a flat roof or round a corner. The survey measures the actual route.