Size the room, choose the practical system, test the window or installation route, model electricity and expose the evidence still missing.
A large BTU number cannot fix an unsuitable exhaust route. A sleep label cannot prove a compressor will suit a light sleeper. A low item price is not the delivered total. The Passport keeps those decisions separate, then joins them into one brief.
The capacity range starts with room volume and adjusts for room use, insulation, sunlight, glazing, occupancy, equipment and top-floor exposure. It deliberately returns a range. It does not claim that a generic rule can replace a professional heat-load calculation.
A portable appliance still needs a safe way to transfer heat outside. An installed split system needs competent design, refrigerant work, condensate management, electrical checks and an acceptable outdoor-unit position. Tenure and building rules remain separate from product capability.
The nightly figure uses the displayed tariff, intended hours and an estimated maximum-input band derived from the capacity range. It is not a bill prediction. The exact model's published cooling input, cycling behaviour and tariff period must be checked before relying on it.
The result does not turn unknown sound, permission or checkout information into a green tick. Those gaps remain marked for verification, so a copied brief can be challenged by another retailer, landlord, freeholder or installer.
Keep the room assumptions while checking products, costs and installation evidence.
Sources reviewed 7 September 2026. Approved Document O applies to new residential buildings in England; it is not a general approval or sizing rule for every existing home. Fixed air conditioning can require building-regulations checks, and refrigerant work may require appropriately certified people or businesses.
GOV.UK: keep cool at home checklist ↗