Walkthrough: a heat pump on a listed terrace

Installing a heat pump at a listed building starts from one fixed point: the permitted development right for air source heat pumps does not apply within the curtilage of a listed building. So you need planning permission for the unit and listed building consent for the works inside. The walkthrough below is illustrative, assembled from the issues these projects raise rather than from any single real case, and it follows a Grade II mid terrace house from first enquiry to decision.

The unit itself was approved in eight weeks. The pipe route took three rounds of drawings.

The house, the listing and the heating problem

An early nineteenth century brick terrace of eight houses, listed Grade II as a group, two rooms deep with a two storey rear outrigger and a 9 m walled garden. Sash windows throughout, original plaster cornices to the front rooms, a stone flagged hall and a back addition added around 1900.

The heating was a twenty year old gas boiler in a first floor cupboard feeding small panel radiators, with the pipework run in the floor voids. The owners wanted to stop burning gas and had been told by three installers that the house was unsuitable, which is usually shorthand for the installer not wanting the paperwork.

Nothing about the building made a heat pump unworkable. The difficulty was entirely in the consents and in the flow temperature.

Why permitted development did not apply

Class G of Part 14 of Schedule 2 to the GPDO 2015 permits an air source heat pump on domestic premises, subject to limitations and conditions, and one of those limitations removes the right where the building is listed or sits within the curtilage of a listed building. That exclusion is absolute and there is no workaround.

Class G has been amended more than once in recent years, including changes to the volume limit and the separation from boundaries, so check the current text of the Order before advising anyone on a non listed property. None of that helps here.

The result was two applications running in parallel:

1. A full planning application for the external unit, its enclosure and any visible pipework, because the installation affects the external appearance of the building and is development requiring permission.
2. An application for listed building consent under section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990 for the works affecting the building's special interest, which turned out to be the larger part of the submission.

Both went in together, which the council prefers because the two decisions have to be consistent.

Siting options, and the one that worked

Four positions were drawn and three were discarded.

The front garden was discarded immediately. A unit visible in the street elevation of a listed terrace is a non starter, and the front gardens were around 1.5 m deep.

The flat roof of the rear outrigger was discarded on two grounds. It would have been visible from the upper windows of the houses behind, and fixing a frame through a historic roof structure is exactly the kind of intervention a conservation officer resists.

A position against the rear wall of the main house was discarded for airflow. The walled yard at that point is narrow and the unit would have been recirculating its own discharge air in winter.

What worked was a position in the garden, roughly 4 m from the rear wall, set against the boundary wall on a low concrete plinth with a timber slatted screen on three sides and open to the garden for airflow. Not visible from the street. Visible from two neighbours' upper rear windows, which the design and access statement addressed directly rather than claiming otherwise.

The condensate run and the flow and return pipes then had to get from the garden into the house, which became the whole of the listed building consent argument.

Noise and the neighbour's bedroom window

Terraces make this harder than detached houses because the assessment position is close.

The Microgeneration Certification Scheme planning standard for air source heat pumps works to a limit of 42 dB(A) at the assessment position, which is taken 1 m from the nearest habitable room window of a neighbouring property. The calculation accounts for the distance, the acoustic performance of the unit at the stated operating point, and the effect of barriers and reflecting surfaces.

For this house the nearest neighbouring habitable room window was a first floor bedroom about 7 m from the proposed position, with the boundary wall offering partial screening at ground level but nothing at first floor. The calculation passed with margin on the manufacturer's quoted figures, and the screen enclosure improved it further.

Two practical notes from that exercise. Manufacturers quote sound power at a defined operating point, and the unit is louder in defrost cycles on a cold damp morning than in the quoted condition. Allow for that rather than submitting the headline figure. And where the calculation is close, a short noise impact assessment prepared properly is worth more than an installer's spreadsheet, because the environmental health officer will read it rather than take it on trust.

Listed building consent and the pipe route

This is where the three rounds of drawings went.

The first proposal ran the pipes through the rear wall into the kitchen, along the skirting, and up through the floor voids to a new cylinder in the first floor cupboard. The conservation officer objected to three elements: a new penetration through historic brickwork in a visible position, surface pipework crossing an original stone flagged floor, and the removal of a section of early skirting.

The approved route did the following. The wall penetration moved into the later 1900 back addition, where the brickwork is of lower significance, and was formed by removing and reinstating a single brick rather than coring. The pipes then ran within the back addition and into the existing floor void using an opening already cut for the gas pipe in the 1990s. The flagged floor was left untouched. The skirting was removed as a complete length, numbered, stored and reinstated, which the schedule of works recorded.

The statutory duty under sections 16 and 66 of the 1990 Act is to have special regard to the desirability of preserving the building and its features of special interest. In practice that means a conservation officer will accept intervention in later or altered fabric and resist it in original fabric, and the whole exercise is finding the route through the former. A heritage statement that assesses significance element by element, naming which fabric is early and which is later, is what allows that conversation to happen.

Radiators were the other listed building point. Lower flow temperatures need larger emitters, and three rooms needed radiators roughly a third larger. In the front rooms that meant fixing below the original dado and clear of the cornice, with the pipe drops in existing chases.

Fabric measures considered alongside

A heat pump into a leaky house is an expensive way to be cold, and the council asked about this directly.

What was done: loft insulation topped up to current depth with the joists left exposed, draught proofing to all sashes, insulation to the suspended timber ground floor from below where there was crawl space, and secondary glazing to the rear elevation only. What was deliberately not done: replacement windows, internal wall insulation to the front rooms, and any sealed vapour barrier, because traditional solid walls need to breathe and Historic England's technical advice on energy efficiency in older buildings is clear about the risk of trapping moisture.

Secondary glazing to the front elevation was discussed and left for a later application, since slim units behind sashes are usually acceptable and the owners had run out of appetite.

The documents submitted and the decision

The planning application carried a planning statement, elevations and a site plan showing the unit and screen, the noise calculation and photographs of the proposed position from the neighbouring windows. The listed building consent application carried a heritage statement, a design and access statement, which Article 9 of the Development Management Procedure Order requires for listed building consent, a room by room schedule of works, and 1:20 drawings of the wall penetration and the radiator positions.

Both were approved with conditions: the screen in a stated timber specification, the pipe route as drawn with no variation without approval, reinstatement of the skirting, and a requirement that the unit be removed and the fabric made good if it ceases to be used.

Grant funding under the Boiler Upgrade Scheme ran separately and required an accredited installer, which is worth lining up before the consents rather than after. The full list of report types is a reasonable prompt for what a listed building project of this kind needs.

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.

Enter your postcode on PlanScope to see which documents a heat pump application at a listed property would need.