The hydrobox is a wall-mounted cabinet roughly the size of a boiler, or it can be built into a combined cylinder unit. It holds the heat exchanger, circulating pump, valves and controls. Outdoor units for split systems can be more compact than monobloc units of similar output, which helps where outdoor space is limited.
In Buckinghamshire, a hydrobox often goes in an utility room or garage, with the cylinder alongside. Flats and terraces in Buckinghamshire with a small yard or flat roof can suit a compact split outdoor unit. In Buckinghamshire homes where the clearest unit position is away from the plant cupboard, a split system allows a longer route indoors.
Who it suits
- Homes where the outdoor unit must sit some distance from the plant space
- Houses with indoor wall space for a boiler-sized hydrobox
- 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 Buckinghamshire
The ranges below are typical installed prices for homes in Buckinghamshire, including VAT. A survey sets the exact figure, because two similar-looking houses in Buckinghamshire 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 | £10,000–£13,150 | £2,500–£5,650 |
| 2–3 bedroom terrace or semi | 5–7 kW | £11,050–£14,200 | £3,550–£6,700 |
| 3 bedroom semi or small detached | 6–9 kW | £12,600–£16,300 | £5,100–£8,800 |
| 4 bedroom detached | 8–12 kW | £14,700–£18,900 | £7,200–£11,400 |
| 5+ bedroom or larger older house | 11–16 kW | £17,350–£23,650 | £9,850–£16,150 |
Installed, inc VAT: unit, cylinder, controls, minor pipework and commissioning.
Towns we cover in Buckinghamshire
We cover 13 towns in Buckinghamshire for split system heat pumps. Each links to local guide prices and the grant position for England.
| Town | Postcode district | Nearest town | Midwinter daylight |
|---|---|---|---|
| Milton Keynes | MK9 | Bletchley | 7 h 44 min |
| High Wycombe | HP11 | Marlow | 7 h 48 min |
| Aylesbury | HP20 | Princes Risborough | 7 h 46 min |
| Bletchley | MK2 | Milton Keynes | 7 h 44 min |
| Amersham | HP7 | Chesham | 7 h 48 min |
| Chesham | HP5 | Amersham | 7 h 48 min |
| Gerrards Cross | SL9 | Chalfont St Peter | 7 h 49 min |
| Chalfont St Peter | SL9 | Gerrards Cross | 7 h 48 min |
| Marlow | SL7 | High Wycombe | 7 h 49 min |
| Beaconsfield | HP9 | Chalfont St Peter | 7 h 48 min |
| Buckingham | MK18 | Brackley | 7 h 44 min |
| Olney | MK46 | Milton Keynes | 7 h 43 min |
| Princes Risborough | HP27 | Aylesbury | 7 h 47 min |
Split system heat pumps questions
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.
Do I need an F-gas engineer for a split heat pump?
Yes. Split systems usually use a fluorinated refrigerant such as R32, so installing, servicing or repairing the refrigerant circuit must by law be done by an F-gas certified engineer. That covers joining the refrigerant pipes, testing them for leaks and charging the system. Your quote sets out who carries out each part of the installation, including the refrigerant work.
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.
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.