What size unit does a home office need?
A 20 m² home office with a 2.4 m ceiling and double glazing needs ≈2.0 kW on Daikin UK’s rule of thumb (checked 25 Sep 2026). The planning test is the same Class G test as the rest of the house if the outdoor unit is on a rear wall.
computed
Worked case from the decision engine
Result on the facts named above: permitted development.
Daikin says computers add cooling demand and publishes +0.18 kW per person above two. It does not publish a separate watts figure for screens, so that 0.18 kW is the add-on to type in if more than two people share the room.
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-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