What size air conditioning does an office need?
How cooling loads are worked out for offices: occupancy, IT, lighting, glazing and orientation, with rule-of-thumb W/m² figures and why a survey matters.
Short answer
As a rough guide, offices need about 80–125 W of cooling per square metre, so a 50 m² office might need about 4–6 kW. Dense occupancy, lots of IT, large south- or west-facing windows and top-floor rooms push the figure up. A heat load calculation per zone gives the real answer.
Where the heat comes from
Cooling has to remove heat from several sources at once. In a typical office the main ones are:
- People — roughly 100 W each when seated
- Computers, screens and printers
- Lighting
- Sun through windows, especially south- and west-facing glass
- Heat through walls and roofs, particularly top floors
Rule-of-thumb figures
Rules of thumb are useful for budgeting but not for buying equipment. A lightly used office with good shading may need about 80 W/m²; a densely occupied, glazed office can need 125 W/m² or more. Meeting rooms need sizing for their maximum occupancy, not their average.
- 30 m² meeting room for 12 people: often 4–5 kW
- 50 m² open-plan office: about 4–6 kW
- 150 m² office floor: about 12–19 kW across several zones
Why oversizing is a problem
A unit that is too big cools the room quickly, then switches down or off before it has removed moisture. The room feels cold and clammy, the unit cycles more, and you paid more for it. Inverter units cope better, but correct sizing still matters.
What a survey records
- Room dimensions and ceiling heights
- Window sizes, orientation and shading
- Occupancy and hours of use
- IT and equipment loads
- Insulation, roof and wall construction
- Where indoor and outdoor units can go
Questions
How many kW per square metre for an office?
About 0.08–0.125 kW per m² as a rough guide; a survey gives the real figure.
Should the comms room be on the office system?
No. Comms rooms need dedicated cooling that runs 24/7.
Related services
- Office air conditioning
- HVAC design and heat load surveys
- Server room and comms room cooling
- Ceiling cassette air conditioning
This guide is general information, not legal advice. Rules can change; check the current position with the relevant authority for your building.