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 Merseyside homes where the clearest unit position is away from the plant cupboard, a split system allows a longer route indoors. Flats and terraces in Merseyside with a small yard or flat roof can suit a compact split outdoor unit. Owners across Merseyside can compare split and monobloc designs side by side at a survey in Merseyside.
Who it suits
- Houses with indoor wall space for a boiler-sized hydrobox
- Owners who would rather not use glycol or anti-freeze valves
- Small yards, roofs or balconies that suit a more compact outdoor unit
- Exposed or frost-prone sites where outdoor water pipes would be a risk
Grants and rules for heat pumps in England
Homes in Merseyside can use the Boiler Upgrade Scheme, which takes £7,500 off the cost of an air source heat pump when it replaces fossil-fuel or electric heating. Replacing oil or LPG heating qualifies for £9,000 for installations from 21 July 2026 to 31 March 2027, and air-to-air systems for £2,500. The MCS-certified installer named in your quote applies for the grant and deducts it from the price.
There is no VAT on installing a heat pump anywhere in the UK until 31 March 2027. In England most houses can have an air source heat pump under permitted development, provided the unit meets the MCS noise and siting standards; the old 1 m boundary limit was removed on 29 May 2025. We flag listed buildings, flats and sensitive conservation-area positions at survey.
Split system heat pumps prices in Merseyside
These are guide prices for Merseyside, installed and including VAT. Your final price is fixed in a written quote after the survey and depends on the heat loss of the house, the radiators that need changing and where the unit goes.
| Home | Typical size | Installed guide price | After £7,500 grant |
|---|---|---|---|
| 1–2 bedroom flat or small terrace | 4–5 kW | £9,200–£12,150 | £1,700–£4,650 |
| 2–3 bedroom terrace or semi | 5–7 kW | £10,200–£13,100 | £2,700–£5,600 |
| 3 bedroom semi or small detached | 6–9 kW | £11,650–£15,050 | £4,150–£7,550 |
| 4 bedroom detached | 8–12 kW | £13,600–£17,450 | £6,100–£9,950 |
| 5+ bedroom or larger older house | 11–16 kW | £16,000–£21,850 | £8,500–£14,350 |
Installed, inc VAT: unit, cylinder, controls, minor pipework and commissioning.
Towns we cover in Merseyside
We cover 14 towns in Merseyside for split system heat pumps. Each links to local guide prices and the grant position for England.
| Town | Postcode district | Nearest town | Midwinter daylight |
|---|---|---|---|
| Liverpool | L3 | Birkenhead | 7 h 29 min |
| Birkenhead | CH41 | Liverpool | 7 h 29 min |
| St Helens | WA10 | Prescot | 7 h 29 min |
| Southport | PR8 | Formby | 7 h 26 min |
| Wallasey | CH45 | Birkenhead | 7 h 29 min |
| Bootle | L21 | Wallasey | 7 h 28 min |
| Bebington | CH63 | Birkenhead | 7 h 30 min |
| Huyton | L36 | Prescot | 7 h 29 min |
| Kirkby | L32 | Maghull | 7 h 28 min |
| Prescot | L34 | Huyton | 7 h 29 min |
| Heswall | CH60 | Bebington | 7 h 30 min |
| Maghull | L31 | Kirkby | 7 h 28 min |
| Formby | L37 | Maghull | 7 h 27 min |
| Halewood | L26 | Huyton | 7 h 30 min |
Split system heat pumps questions
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.
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.
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.