Air source heat pumps at a listed building

Installing an air source heat pump at a listed building almost always needs listed building consent, even where the pump itself would otherwise be permitted development. The two consents are separate. Permitted development rights under Part 14 of the General Permitted Development Order deal with the planning position and are restricted at listed buildings, while listed building consent is required for any works affecting the character of the building, which includes the fixings, the pipe penetrations and the internal changes to emitters.

So the question is rarely whether consent is needed. It is what you put in the application.

The permitted development position

Part 14 Class G covers air source heat pumps on domestic premises, subject to conditions on siting, size and noise. The class has been amended more than once in recent years, including changes to the number of units and the boundary restrictions, so read the current text rather than relying on a summary.

What has stayed constant is the listed building position. Part 14 rights are restricted where the dwelling is listed or within the curtilage of a listed building, and even where a right exists, it does not remove the separate requirement for listed building consent. Unauthorised works to a listed building are a criminal offence with no enforcement time limit, so this is not a risk worth running.

Two further checks before design. An Article 4 direction may have removed rights in the surrounding conservation area, and a conservation area carries its own consent considerations for works visible from the street. Where the pump will be visible from a highway, assume full scrutiny.

Listed building consent for fixings and pipe runs

The detail that worries conservation officers is not the box. It is the holes.

A wall-mounted pump needs brackets fixed into masonry. On soft handmade brick, ashlar stone or lime-rendered rubble, those fixings cause loss that cannot be reversed, and on a rubble wall they may not be structurally reliable either. The accepted answer in most cases is a ground-mounted unit on its own frame or plinth, standing clear of the building, with no load taken by historic fabric.

Pipe runs then become the issue. Two flow and return pipes, a condensate drain and an electrical supply have to reach the plant room. Drilling new openings through a thick solid wall is a loss, and four separate penetrations are four losses. The approaches that get approved share a logic.

• Use existing openings wherever they exist: a redundant flue, an old soil pipe penetration, an airbrick, a coal hole or a disused service entry.
• Group all services into a single penetration rather than several.
• Enter through a later addition, a modern extension or a rebuilt section rather than through original fabric.
• Run pipes below ground and enter beneath a suspended timber floor, where access permits.
• Where a new penetration is unavoidable, core through a mortar joint rather than through a brick or a dressed stone face, and make it reversible with a sleeve.

Siting to reduce visual effect

Officers assess the pump as they would any plant: what you see from where. Set the test out explicitly in the application rather than leaving it to a site visit.

Screening needs care of its own. A close-boarded enclosure built hard against a listed wall is itself an alteration, and it can restrict the air flow the unit needs. Freestanding screens set away from the building, or planting, are usually the better answer, and the manufacturer's clearance requirements have to be shown on the drawing.

Noise assessment expectations

The microgeneration certification scheme planning standard sets the noise test used for domestic heat pumps, calculating the sound level at a defined assessment position close to a neighbouring habitable room window and comparing it with a limit. The current version of the standard and its limit figure should be taken from the scheme itself, since the document has been revised.

The calculation depends on the manufacturer's declared sound power level, the distance to the assessment position, and whether the unit sits against a reflecting surface or in a corner, which can add several decibels. Put the completed calculation in the application. Where the site is tight, or where a neighbour's window is close, a short Noise Impact Assessment from an acoustician is worth more than an argument about the standard.

Night operation matters more than the daytime figure. A unit that is acceptable at 2pm can generate complaints at 3am when it defrosts, so locate it away from bedroom windows on both properties and specify a model with a quiet mode if one is available.

Pipe runs through historic fabric

Internally, the losses are cumulative and small, which is how they get overlooked in an application and then refused.

Lifting original floorboards to run pipework is usually acceptable if the boards are numbered, lifted carefully and relaid. Notching historic joists is not, and a modern pipe route under a suspended floor should run between joists or below them. Chasing plaster to drop pipes down a wall destroys historic plaster, and surface-mounted pipework in a discreet location is frequently preferred by conservation officers to hidden pipework that cost fabric to conceal.

Boxing in should be reversible and should not cut into skirtings, architraves or panelling. Where original joinery has to be eased, keep the removed sections on site, because the honesty of repair argument depends on being able to put things back.

Internal changes to emitters

A heat pump runs at a lower flow temperature than a gas boiler, so emitters have to be larger. In a listed house that collides with the fabric in three places.

Larger radiators need more wall, and the obvious walls are often the ones with panelling, shutters or a fireplace. Underfloor heating in a historic solid floor means excavating the floor and changing its moisture behaviour, and over a suspended timber floor it changes the thermal regime around the joist ends. And fan-assisted emitters, while compact, introduce a mechanical noise into rooms that have none.

The practical sequence is to improve the fabric first within what consent allows, then size the emitters to the reduced load. Draught-proofing, working shutters, secondary glazing and loft insulation reduce the heat requirement and therefore the size of every radiator in the house. That order of work is also the order conservation officers prefer.

What to submit

An application that goes through first time contains the following.

1. A statement of significance for the building and for each area affected, which is the substance of a Heritage Statement.
2. A site plan showing the unit's position, its clearances, and the viewpoints from which it would be visible.
3. Elevations and a plan showing the unit, any screening and every penetration, with each penetration annotated as existing or new.
4. A detail at 1:5 or 1:10 of the penetration, showing the sleeve, the make good and the reversibility.
5. The noise calculation under the current scheme standard, with the declared sound power level and the assessment position marked.
6. A schedule of internal works room by room, with the emitter changes and the pipe routes.
7. Photographs of every surface affected, taken before any work.

Note: the condensate drain is the item most often missing from these applications, and an officer who spots a heat pump with no condensate route will ask about it.

Draft a Heritage Statement on PlanScope and send it for professional review before you apply.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.