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.
Installers covering Gwynedd keep refrigerant routes neat and protected along the outside wall. Properties on exposed sites around Gwynedd can avoid outdoor water pipes altogether with a split system. In Gwynedd, a hydrobox often goes in an utility room or garage, with the cylinder alongside.
Who it suits
- Exposed or frost-prone sites where outdoor water pipes would be a risk
- Homes where the outdoor unit must sit some distance from the plant space
- Houses with indoor wall space for a boiler-sized hydrobox
- Small yards, roofs or balconies that suit a more compact outdoor unit
Grants and rules for heat pumps in Wales
Homes in Gwynedd can use the Boiler Upgrade Scheme, which applies in Wales as well as England: £7,500 towards an air source heat pump, or £9,000 when it replaces oil or LPG heating for installations from 21 July 2026 to 31 March 2027. The MCS-certified installer named in your quote applies and deducts the grant.
Installing heat pumps is zero-rated for VAT across the UK until 31 March 2027. Wales has its own permitted development rules for air source heat pumps, so we check what applies to your property, including listed building and conservation-area constraints, at the survey.
Split system heat pumps prices in Gwynedd
These are guide prices for Gwynedd, 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 | £9,500–£12,500 | £2,000–£5,000 |
| 2–3 bedroom terrace or semi | 5–7 kW | £10,500–£13,500 | £3,000–£6,000 |
| 3 bedroom semi or small detached | 6–9 kW | £12,000–£15,500 | £4,500–£8,000 |
| 4 bedroom detached | 8–12 kW | £14,000–£18,000 | £6,500–£10,500 |
| 5+ bedroom or larger older house | 11–16 kW | £16,500–£22,500 | £9,000–£15,000 |
Installed, inc VAT: unit, cylinder, controls, minor pipework and commissioning.
Towns we cover in Gwynedd
We cover 9 towns in Gwynedd for split system heat pumps. Each links to local guide prices and the grant position for Wales.
| Town | Postcode district | Nearest town | Midwinter daylight |
|---|---|---|---|
| Bangor (Gwynedd) | LL59 | Beaumaris | 7 h 31 min |
| Bala | LL23 | Dolgellau | 7 h 35 min |
| Beaumaris | LL58 | Bangor (Gwynedd) | 7 h 31 min |
| Caernarfon | LL55 | Llangefni | 7 h 32 min |
| Dolgellau | LL40 | Machynlleth | 7 h 36 min |
| Holyhead | LL65 | Llangefni | 7 h 30 min |
| Llangefni | LL77 | Bangor (Gwynedd) | 7 h 31 min |
| Porthmadog | LL49 | Pwllheli | 7 h 34 min |
| Pwllheli | LL53 | Porthmadog | 7 h 35 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.
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.
Is a split system more efficient than a monobloc?
Not inherently. Efficiency depends far more on design, meaning correct sizing, low flow temperatures and good controls, than on whether the unit is split or monobloc. A split system can avoid the heat loss and glycol of a long outdoor water run, which helps in certain layouts. The survey estimates seasonal efficiency for the specific units proposed, so you can compare like for like.