Heat pumps for flats and terraced houses

Where the outdoor unit can go

An air source heat pump needs an outdoor unit, and flats and terraces are short of outdoor space. The Class G permitted development rules narrow the options further. The unit can go on a wall of the dwelling or block, on land within its curtilage, or on a flat roof (at least 1 metre from the external edge), but not on a pitched roof. In a conservation area, or on a wall facing the road above ground-floor level elsewhere, the position tests described in heat pump planning permission remove the street side of the building. That usually leaves the rear wall, the ground at the back, a side return, or a flat roof or balcony, each with a different noise and access consequence.

For a ground-floor or maisonette flat, a rear garden or yard is the natural place. For an upper-floor flat, the realistic choices are a wall-mounted unit, a balcony, or a roof, and each is likely to need the freeholder’s agreement because they involve parts of the building you do not own. Where nothing outdoors works, the question becomes whether another system, shared plant or a different heat source is a better fit; an installer’s survey should say so rather than force a unit in.

The planning limits for flats and terraces

• Terraced houses: a house that is not detached can have no more than 1 air source heat pump on, or within the curtilage of, the house. The outdoor unit, including any housing, must not exceed 1.5 cubic metres.
• Blocks of flats: no more than 1 air source heat pump on, or within the curtilage of, the block; the unit must not exceed 0.6 cubic metres. Read literally, that is one for the whole block, not one per flat, so a second installation in the same block is outside Class G and needs planning permission.
• Ground source: Class C grants permission for a ground source heat pump within the curtilage of a dwellinghouse or block of flats, with no number or volume limits. A shared ground loop may therefore avoid the one-unit air source limit for a block; whether Class C covers a loop serving several properties depends on the curtilages involved, so ask the council, and other consents outside Part 14 may apply.

These are England’s rules, read on 8 October 2026. Wales and Scotland have their own; see the planning guide.

Flats have tighter permitted development limits than houses, including a smaller 0.6 cubic metres outdoor unit, and the full set is on heat pump planning permission.

The noise test when windows are close

In a terrace, the neighbour’s window may be only a few metres from where the unit would stand. The MCS 020 a) calculation takes the sound power of the unit, the number of reflecting surfaces within a metre of it, the distance to the assessment position and any solid barrier, and the result at every neighbouring window or door of a habitable room must be 37.0 dB(A) or less. The standard warns that assessment positions should include neighbours on all sides and at every floor, and that a unit with more than three reflecting surfaces (a lightwell, say) will not meet it. Reflecting surfaces matter in terraces because side passages and rear yards enclose a unit on several sides.

The Institute of Acoustics and CIEH note says cumulative noise from many units is unlikely to be a problem for detached, semi-detached and terraced houses on recent research, and only needs considering for courtyards or flats depending on the local context. If you are in a courtyard or a block where several owners may fit units, expect the council or the freeholder to take a closer interest. The full method and a calculator are on heat pump noise.

London has the lowest heat pump grant take-up in England, and flats are part of the reason the question is harder there; the heat pump grants in London page sets out the borough figures and the council route.

Leasehold, freeholders and rented homes

Planning permission is not the only consent. LEASE says that, depending on the terms of your lease, you might need your landlord’s permission before making alterations even if you already have planning permission, that the demised premises of a flat do not usually include structural or external walls or the roof, and that where an alteration involves parts the landlord owns or controls, they may not be bound by the usual rules on reasonable refusal: ask LEASE about your own lease. Nesta’s project on heat pumps in flats (freeholder focus groups) reports that freeholders it spoke to generally treated heat pump requests case by case, with fire safety, building integrity, workmanship and who maintains the system if the leaseholder sells as the typical concerns. Practical steps:

1. Read the lease for clauses on alterations, external walls, roofs, balconies and shared pipework.
2. Write to the freeholder or managing agent early with the installer’s proposed position, noise calculation and method statement.
3. Agree maintenance and responsibility if the property is sold.

For the grant itself, Ofgem’s guidance says you must become the legal owner of the new heat pump, so arrangements where a finance provider or the installer keeps ownership are not eligible; and if you are a landlord, you must make sure you have informed any tenant about the installation. Social housing (including shared ownership) and most new builds are usually not eligible. The full test is on the eligibility page, and how to find and compare installers explains how to get quotes.

Shared ground loops

A shared ground loop is one ground loop serving several properties, each with its own heat pump. Ofgem’s guidance (version 5.1) says that where this applies each property must have its own voucher application, and consent must be provided separately for each property owner; your installer will explain whether it applies to you. The scheme’s capacity limit for a shared ground loop is 300 kWth, against 45 kWth for a single system. Terraces and small developments are where this arrangement is most often discussed, and it may sidestep the one-unit air source limit, because Class C has no number limits (whether it applies to a loop serving several properties depends on the curtilages; ask the council). The ground and borehole side is covered on the ground source grant page.

Inside: cylinder, radiators and the grant

The inside of a flat has its own constraints. A heat pump needs a hot water cylinder, and the government’s heat pump explainer says heat batteries are an option for consumers with limited space; the space and sizing questions are on hot water cylinders for heat pumps. Radiators and pipework are checked through the heat loss assessment, covered in sizing and radiators; the installer’s room-by-room calculation is what decides what each room needs.

The grant is £7,500 for an eligible air source or ground source installation, deducted on the installer’s quote (£9,000 for eligible homes with no mains gas that are replacing oil or LPG, for applications up to 31 March 2027). Check where you stand, then ask installers for quotes that show the position of the unit and the noise result.