What changes when the flat is rented?
A rented flat in a building that is wholly flats can still be permitted development with one outdoor unit within 0.6 m³ on a wall that does not face a highway (Class G, checked 25 Sep 2026). The tenancy is a separate ask: in England the fitness covenant names ventilation and any prescribed hazard, including excess heat.
computed
Worked case from the decision engine
Result on the facts named above: permitted development.
Excess heat. Exposure to high temperatures. The letter tool fills the district’s hot-night count.
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-14 · interpretation, ‘block of flats’ · checked 25 Sep 2026. “block of flats” means a building which consists wholly of flats 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-09 · G.2(i) · checked 25 Sep 2026. the air source heat pump would be installed on a building or on land within the curtilage of the dwellinghouse or the block of flats if the dwellinghouse or the block of flats is a listed building Source
Next pages
· · n= · · updated 25 Sep 2026 · version 1.0.0 · CSV of the values on this page