Choosing the right size air conditioner is about more than floor area. BTU and kW describe cooling output, but the real requirement also depends on ceiling height, glazing, sun exposure, insulation, people in the room and equipment such as computers.
BTU and kW in plain English
BTU stands for British Thermal Unit and is commonly used for portable air conditioners. kW is commonly used for fixed split systems. As a rough comparison, 2.5 kW is around 8,500 BTU and 3.5 kW is around 12,000 BTU.
A small bedroom may suit a lower-output system, while a larger living room, loft conversion or open-plan area may need more capacity. Oversizing is not always better because a unit that is too powerful can cycle poorly and feel less comfortable.
London rooms that need extra care
Loft rooms, top-floor flats, south-facing bedrooms, large glass doors and poorly insulated extensions often need more careful sizing. The room may heat up quickly during summer even if the floor area looks modest.
Simple pre-survey checklist
- Measure the room length, width and approximate ceiling height.
- Note whether the room faces south or west.
- Take photos of windows, doors and the wall where the unit may go.
- Tell the installer how many people use the room and whether it has computers or other heat-producing equipment.
For work-from-home rooms, add details about how many screens run through the day and where the desk sits in relation to the window. City Air’s home office air conditioning guide explains why those details matter when you want quiet, all-day comfort.
City Air can use this information to suggest likely model sizes before confirming the final specification during survey.
