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.
Properties on exposed sites around Northumberland can avoid outdoor water pipes altogether with a split system. In Northumberland, a hydrobox often goes in an utility room or garage, with the cylinder alongside. Flats and terraces in Northumberland 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
- Small yards, roofs or balconies that suit a more compact outdoor unit
- Owners who would rather not use glycol or anti-freeze valves
- Houses with indoor wall space for a boiler-sized hydrobox
Grants and rules for heat pumps in England
Homes in Northumberland 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.
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 Northumberland
These are guide prices for Northumberland, 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 | £9,400–£12,400 | £1,900–£4,900 |
| 2–3 bedroom terrace or semi | 5–7 kW | £10,400–£13,350 | £2,900–£5,850 |
| 3 bedroom semi or small detached | 6–9 kW | £11,900–£15,350 | £4,400–£7,850 |
| 4 bedroom detached | 8–12 kW | £13,850–£17,800 | £6,350–£10,300 |
| 5+ bedroom or larger older house | 11–16 kW | £16,350–£22,300 | £8,850–£14,800 |
Installed, inc VAT: unit, cylinder, controls, minor pipework and commissioning.
Towns we cover in Northumberland
We cover 10 towns in Northumberland for split system heat pumps. Each links to local guide prices and the grant position for England.
| Town | Postcode district | Nearest town | Midwinter daylight |
|---|---|---|---|
| Blyth | NE24 | Bedlington | 7 h 08 min |
| Cramlington | NE23 | Bedlington | 7 h 09 min |
| Ashington | NE63 | Bedlington | 7 h 08 min |
| Bedlington | NE22 | Cramlington | 7 h 08 min |
| Alnwick | NE66 | Morpeth | 7 h 05 min |
| Berwick-upon-Tweed | TD15 | Alnwick | 7 h 00 min |
| Hexham | NE46 | Prudhoe | 7 h 10 min |
| Morpeth | NE61 | Bedlington | 7 h 08 min |
| Ponteland | NE20 | Cramlington | 7 h 09 min |
| Prudhoe | NE42 | Newburn | 7 h 10 min |
Split system heat pumps questions
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.
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.
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.