Permitted development in one paragraph
England's General Permitted Development Order grants planning permission in advance for certain small works, as long as they meet set conditions. Part 14 of the order covers renewable energy, and two of its classes cover heat pumps: Class G for air source and Class C for ground source. If a heat pump meets every condition in its class, no application is needed. If it misses one, you apply to the council in the normal way. The same rules apply in all 14 Lancashire councils.
Class G: air source on a house or flats
The conditions, in plain terms:
- How many: one unit on a terraced or semi-detached house or a block of flats; up to two on a detached house.
- How big: the outdoor unit and any housing no more than 1.5 cubic metres on a house, or 0.6 on a block of flats.
- Roofs: never on a pitched roof; on a flat roof, no closer than a metre to the edge.
- Walls facing a road: never above the ground floor; in a conservation area, not on any wall or roof that fronts a road, and not nearer the road than the house.
- Sound: the installation meets the MCS 020 a) planning standard.
- Protected buildings: never on a listed building or within its grounds, or on a scheduled monument.
- Upkeep: positioned, as far as practicable, to limit its effect on the look of the building and on neighbours, and removed when no longer needed.
The rules were relaxed in England in May 2025. The old requirement to keep a unit a metre from the boundary went, the size limit on a house rose to 1.5 cubic metres, and detached houses gained the right to a second unit.
What the house type means here
Lancashire's housing makes the number rule matter. Across the 14 councils, 30.8% of households lived in a terraced house and 34.1% in a semi-detached one in 2021, so most homes can have one unit. 21.8% lived in detached houses, rising to 34.5% in the Ribble Valley, where a larger farmhouse can use two. 60,992 households lived in purpose-built blocks of flats, where the smaller size limit and the building owner's agreement both come into play.
Position is the other practical limit. In Pendle, where 52.7% of households lived in terraces, the front wall usually meets the pavement, so the back yard or rear wall is the realistic spot. On a semi-detached house the side or rear is usually free. On a detached house in the country the choice is wide, and distance from any neighbour makes the sound calculation easier.
The sound calculation
MCS 020 a) is the test that turns noise into a yes or no. The installer takes the unit's sound power level, the distance to the nearest habitable room window of a neighbouring home, the number of reflecting surfaces nearby and any solid barrier in between, and works out the level at that window. If it is at or below the limit, the sound condition is met. If not, a different unit, a different position or a barrier can change the result; otherwise an application is needed.
Keep a copy of the calculation. It is the evidence that the installation is permitted development, and it helps if a neighbour ever asks.
Class C: ground source
Class C covers installing, altering or replacing a ground source heat pump within the grounds of a house or block of flats. It has none of Class G's size, number or position conditions, because the working parts are underground and the plant inside. That makes ground source simpler in planning terms, though the trenches or borehole need space and access. Check with the council if the house is listed or the land holds anything protected, such as a scheduled monument.
Conservation areas
Lancashire's councils have conservation areas in town centres, mill villages, estates and coastal streets. In one, Class G still applies, but nothing may sit on a wall or roof fronting a road or between the house and the road. A council can also remove permitted development rights for a particular area with an Article 4 direction, so if you live in a conservation area, check the council's map and any directions before you plan the position. The council's own map is the reliable source.
Listed buildings
Class G does not apply to a listed building or anything in its grounds, so a heat pump at a listed house always needs planning permission, and listed building consent if the work affects the building's character. Lancaster holds 1,343 records in the national dataset and the Ribble Valley 836; Blackpool only 56. The listed buildings page has every council's figure and the route to follow.
When to apply anyway
- The building is listed, or you are not certain it is not.
- The only workable position faces a road in a conservation area.
- You need more units, a larger unit or a position Class G excludes.
- The sound calculation does not pass.
- You want a lawful development certificate as proof that a plan is permitted development, for example before selling.