- Guide price
- From £9,500 inc VAT
- Survey
- Free home survey for installation enquiries
- Coverage
- England, Wales, Scotland and Northern Ireland
A monobloc heat pump is an air-to-water unit with the entire refrigerant circuit, including the compressor, heat exchangers and refrigerant, sealed inside the outdoor casing. Heat is passed to water inside the unit, and insulated water pipes carry it into the house to the cylinder and heating system. Nothing containing refrigerant comes indoors, which is a big part of why monobloc units suit so many UK homes.
Because the refrigerant circuit is sealed at the factory, the installer does not need to handle refrigerant on site in a typical installation, which keeps the job simpler. Inside, you still have a cylinder, controls and a small set of components for the water circuit, such as pumps, valves and an expansion vessel, but there is no indoor refrigerant unit to find wall space for.
The trade-off is that the pipes between the outdoor unit and the house carry water, so they must be protected from freezing. That is done with glycol (an anti-freeze) in the system or with anti-freeze valves that release water from the outdoor pipework if it nears freezing, for example during a power cut in cold weather. Keeping the outdoor pipe run short and well insulated also helps efficiency.
Who it suits
- Houses and bungalows with outdoor space close to where pipes enter the home
- Owners who want the simplest installation, with no indoor refrigerant
- Homes where the unit can sit within a short pipe run of the cylinder
- Households that want to keep refrigerant work out of routine servicing
Things to consider
- Water pipes run outside, so frost protection with glycol or anti-freeze valves must be designed in.
- Long pipe runs between the unit and the house lose heat, so the unit is usually sited close to the building.
- The outdoor unit holds the whole system, so allow space roughly 1 m wide plus the clearances it needs.
- Units using R290 have siting clearances from windows, doors and drains set by the manufacturer.
How does a monobloc heat pump connect to my home?
Two insulated water pipes, a flow and a return, run from the outdoor unit through the wall to the heating system and cylinder. Inside, a set of components manages the water: a circulating pump, a valve that switches between heating and hot water, an expansion vessel and a filter. Depending on the model these sit in a small indoor cabinet, on a pre-plumbed cylinder or on the wall nearby.
The outdoor unit sits on a ground frame, a concrete base or wall brackets, raised to clear snow and let defrost water drain away. A dedicated electrical supply runs from your consumer unit to an isolator beside it.
How is a monobloc system protected from freezing?
Frost protection stops the water in outdoor pipework freezing when the unit is not running, such as during a power cut. The choice is made at design stage:
- Glycol: an anti-freeze mixed into the system water. It protects reliably but slightly reduces efficiency, and its concentration should be checked at servicing.
- Anti-freeze valves: fitted where the pipes leave the unit, they open and release water if it nears freezing. The system water stays plain, but the system must be refilled if they operate.
- The unit's own frost routine: while it has power, the unit circulates water and adds a little heat to keep pipes clear.
Short, well-insulated pipe runs reduce both the frost risk and the heat lost between the unit and the house.
What does a monobloc installation involve?
The installer sets the unit, runs the water pipes and power cable, fits the cylinder and controls, then fills the system, purges the air, pressure tests and commissions it. A typical home installation takes 2–4 days on site, longer if radiators are changed.
The guide price for a full air-to-water system in a three-bedroom semi is £12,000–£15,500, installed and including VAT. The written quote you receive after the survey fixes the final price.
What should I ask about a monobloc unit at survey?
Ask where the unit will go and how long the pipe run will be, which refrigerant it uses, how frost protection will be handled, and how the position meets the MCS noise assessment. For an R290 unit, ask to see the manufacturer's clearance zone marked against your windows, doors and drains, so you know what can and cannot sit nearby later.
What's included
- Free survey covering unit siting, pipe route and noise assessment
- Monobloc outdoor unit on a base, frame or wall brackets
- Insulated flow and return pipework with frost protection
- Heat pump cylinder, indoor water-circuit components and controls
- Dedicated electrical supply and outdoor isolator
- Commissioning and MCS certificate, plus the grant application in England and Wales if you qualify
Monobloc heat pumps guide prices
| 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.
Monobloc heat pumps questions
What is the difference between monobloc and split heat pumps?
A monobloc unit holds all of its refrigerant in the outdoor unit and sends heated water into the house. A split system has an outdoor unit and an indoor unit called a hydrobox, connected by refrigerant pipes, with heat passed to water indoors. Monobloc installs are simpler; splits avoid outdoor water pipes but need an F-gas certified engineer for the refrigerant work. Our monobloc vs split guide compares them.
Do monobloc heat pumps need an F-gas engineer?
For a typical installation no refrigerant work is needed on site, because the refrigerant circuit is sealed in the outdoor unit at the factory. That is one reason monobloc installs are simpler. If the sealed circuit ever develops a fault or leak, any repair to it must be done by an F-gas certified engineer, as with every refrigerant system.
Is glycol or anti-freeze valves the better option?
Neither is right for every home. Glycol gives reliable frost protection without draining but slightly reduces efficiency and needs its concentration checked at servicing. Anti-freeze valves keep the system water plain but release water if pipes near freezing during a power cut, so the system then needs refilling. The installer recommends one based on the unit, pipe run and how exposed the site is.
How far can a monobloc unit be from the house?
Usually as close as practical, because water pipes outside lose heat and need frost protection. Manufacturers set limits on pipe length and size, and longer runs need larger, better-insulated pipes. Most homes site the unit against or near an outside wall close to where the pipes enter. If the only good position is far from the house, a split system may suit better.
Are monobloc heat pumps covered by grants?
Yes. Monobloc units are air-to-water heat pumps, so in England and Wales they are covered by the Boiler Upgrade Scheme grant of £7,500 for eligible homes, or £9,000 when replacing oil or LPG heating within the published dates. In Scotland, Home Energy Scotland funding requires an MCS-certified installer and products. There is no dedicated homeowner heat pump grant in Northern Ireland at present.
What refrigerant do monobloc heat pumps use?
Most use R32 or R290. R290 is propane, a natural refrigerant with a very low global warming impact, and some models use it to reach higher flow temperatures. Because R290 is flammable, manufacturers set clearance zones around the unit from openings such as windows, doors and drains, which the survey takes into account when choosing a position.