Can the outdoor unit go on the rear wall of a terraced house?
For a terraced house the outdoor unit is usually permitted development on the rear wall if it is one unit, within 1.5 m³, not on a listed building, and not used only for cooling (Class G, checked 25 Sep 2026). If the wall faces a highway above the ground floor, that spot is outside Class G.
computed
Worked case from the decision engine
Result on the facts named above: permitted development.
The worked case is a dwellinghouse, one unit, not detached, volume 0.3 m³ (the figure in the Mitsubishi MSZ-RZ25 fixture, entered here as the scenario, not measured on your wall), rear wall not facing a highway, noise entered as a pass.
Volume, noise and listing in the worked case are entered facts. They are not read off the postcode.
Cooling paths
At 400 hours and the Ofgem cap, the split scenario is £27.71 and the portable scenario delivering the same 2.5 kW is £101.23.
| Path | What it is | Up front | £ for 400 h | Open |
|---|---|---|---|---|
| External shading | No outdoor unit | Shelf prices sit in the shade class of the retail file | No compressor draw in the catalogue | /tools/sizing/ |
| Fan | Devola Low Noise 20W 9 Speed 9-inch DC Desk Fan - White - DVF7DCFAN | £59.95 | £2.11 for 400 h at 20 W | /tools/running-cost/ |
| Portable | Cirro® 12000 BTU Super Quiet Smart Portable Air Conditioner - Cooling | £519.99 | £101.23 to deliver 2.5 kW for 400 h at EER 2.6 | /tools/running-cost/ |
| Split / air-to-air | Daikin Perfera 2.5 kW, SEER 9.5 | median shelf £1,027.49 (n=14) | £27.71 for 400 h | /tools/payback/ |
The clauses this situation turns on
ENG-01 · Class G, permitted development · checked 25 Sep 2026. The installation, alteration or replacement of a microgeneration air source heat pump—(a) on a dwellinghouse or a block of flats; or (b) within the curtilage of a dwellinghouse or a block of flats, including on a building within that curtilage. Source
ENG-03 · G.2(a), as substituted by SI 2025/560 art. 5(3)(a) · checked 25 Sep 2026. the development would result in the presence of (i) more than one air source heat pump on, or within the curtilage of—(aa) a dwellinghouse which is not a detached dwellinghouse; (bb) a block of flats; (ii) more than two air source heat pumps on, or within the curtilage of, a detached dwellinghouse Source
ENG-05 · G.2(d), as substituted by SI 2025/560 art. 5(3)(b) · checked 25 Sep 2026. the volume of the air source heat pump's outdoor compressor unit (including any housing) would—(i) … a dwellinghouse, exceed 1.5 cubic metres; (ii) … a block of flats, exceed 0.6 cubic metres Source
ENG-11 · G.2(k) · checked 25 Sep 2026. in the case of land, other than land within a conservation area or which is a World Heritage Site, the air source heat pump would be installed on a wall of a dwellinghouse or block of flats if—(i) that wall fronts a highway; and (ii) … above the level of the ground floor storey Source
ENG-12 · G.3(aa), inserted by SI 2025/560 art. 5(4)(b) · checked 25 Sep 2026. the air source heat pump is not solely used for the purpose of cooling Source
Next pages
· · n= · · updated 25 Sep 2026 · version 1.0.0 · CSV of the values on this page