Air to water heat pumps for landlords

What an air to water heat pump is

An air to water heat pump has an outdoor unit that pulls heat out of the air, even in cold weather, and passes it to water. That warm water then goes where a boiler’s water would go: through radiators or underfloor pipes, and into a hot water cylinder for the taps and showers. The house keeps a wet heating system, with a different heat source.

Because it moves heat rather than making it, it delivers more heat than the electricity it uses. The measure is the seasonal coefficient of performance, SCOP. A SCOP of 3 means three units of heat for each unit of electricity over a year. Your tenants’ bill depends on that figure, on the tariff and on how well the home holds heat, which is why the survey and the design matter more than the brand. The running costs guide for tenants shows what that looks like in pounds.

The same technology is also called an air source heat pump. When an installer says “air source” for a home, they almost always mean air to water. The design rules an installer must follow are set out in MIS 3005-D, the MCS heat pump design standard.

Why it is the default choice

The Department for Energy Security and Net Zero counted 20,895 MCS-certified heat pump retrofits in the first half of 2026, against 26,768 in the first half of 2025, a fall of 22%. In that count, 99% were air to water. Landlords who ask an installer for “a heat pump” will be quoted an air to water system unless they ask for something else.

That is partly the grant. The Boiler Upgrade Scheme pays £7,500 towards an air source or ground source heat pump (£9,000 where oil or LPG is replaced and there is no mains gas), and £2,500 for air to air. The scheme’s own statistics put the median installed cost of an air to water heat pump in the second quarter of 2026 at £12,908, including the grant value. Read that as the price of the job before the grant is taken off, in a year of rising uptake, not as a quote for your property.

It is also the type that fits the way most rentals are already heated. A house with a gas boiler, radiators and a hot water cylinder has the pipework an air to water system needs. Swapping the heat source is a smaller change than installing a new system from scratch.

What it replaces and what it asks of the building

An air to water installation replaces the boiler, and usually the hot water cylinder as well. It adds an outdoor unit, a cylinder suited to heat pump temperatures and some indoor pipework between them. Three things decide whether the job is easy.

The radiators. A heat pump runs the water at a lower temperature than a boiler does. A radiator sized for a boiler may give too little heat at that temperature, so some rooms need larger radiators. The installer sizes each room, using the design standard, before quoting. Ask for the room by room sheet, not just a total.

The cylinder. A home with a combination boiler has no cylinder. Fitting one needs floor space and a position near the heat pump pipework. This is the usual reason an air to water system does not fit a small flat. See heat pumps for flats for the alternatives.

The outdoor unit. It needs a spot with air flow, enough distance from neighbours’ windows for the noise rule, and, in a flat, the freeholder’s agreement. The permitted development rules in England allow one unit on most homes and two on a detached house, subject to a 37.0 dB(A) noise limit and siting conditions that tighten in conservation areas and for listed buildings. The pre-install checklist walks through consent, access and timing.

What the Boiler Upgrade Scheme grant covers, for a landlord

The Boiler Upgrade Scheme is open to the owner of the property, and the rules say that includes a property you rent to tenants. The grant is £7,500 for an air source or ground source heat pump. Where an oil or LPG system is replaced and the property has no mains gas connection, the figure is £9,000, from 21 July 2026 to 31 March 2027.

Four conditions come up again and again for landlords:

• The heat pump must replace an existing fossil fuel or direct electric heating system.
• The home must not already have had government funding for a heat pump or biomass boiler. One grant per property.
• Social housing and most new builds are excluded.
• The installer, who must be MCS-certified, applies for the grant for you, and the installation must be finished within 120 days of the application.

The scheme covers England and Wales. For the detail, with the application steps and the cases that catch landlords out, read the Boiler Upgrade Scheme guide for landlords, and use the funding checker above to see which routes open to a particular property.

When air to water is the wrong answer

An air to water system suits a home that holds heat. It is a poor first step in four common cases:

1. An uninsulated house with a working boiler. Fabric work such as loft insulation comes first, because a heat pump in a draughty house runs hard and costs more to run. See solid wall rentals: heat pump or insulation first.
2. A small flat with no space for a cylinder. Air to air, or a modern electric system, may be the realistic route. See air to air heat pumps for rentals.
3. A tenancy where the tenant pays the electricity and the home is expensive to heat. Electricity costs more per unit than gas, so a poorly performing heat pump can raise a tenant’s bill. The tenant running cost guide covers how to check this before you decide.
4. A short horizon. If you plan to sell soon, the payback may not reach you. The cost guide shows the model.

How to compare quotes as a landlord

Ask every installer for the same four things in writing: the room by room heat loss and radiator sizes, the cylinder size and where it goes, the SCOP the design is based on, and who applies for the grant and when. Check the installer on the MCS register yourself. A quote that gives only a total price and a brand name cannot be compared with another one.

If you want to ask us about your own property, send an enquiry through the form below and we reply by email. We do not install, survey or quote, and there is no installer partner behind this site. The page on how to check an installer lists what to look up.

Sources

The scheme rules and amounts are on GOV.UK. The install count comes from the Department for Energy Security and Net Zero’s heat pump deployment statistics, the median cost from the Boiler Upgrade Scheme statistics, the typical price from Energy Saving Trust, and the noise and siting limits from the planning legislation. Each is listed at the foot of this page with the date it was read.