Size commercial AC to load in kW, not floor area.
A defensible UK sizing benchmark by space type, plus the five drivers that make a 100 m² office anywhere from 8 to 22 kW of cooling. Feasibility numbers, not install-grade — the latter always needs a room-by-room load calc.
Commercial AC is sized to cooling load in kW, not floor area. A mid-glazed UK office typically sits at 80–120 W/m², so a 500 m² floor needs roughly 40–60 kW installed. Server rooms are sized to IT load × 1.1–1.3, ignoring area. All install-grade sizing needs a room-by-room CIBSE load calculation — floor-area estimates are feasibility only.
UK cooling load benchmarks by space type.
| Space | Cooling load (W/m²) | Per 100 m² | Notes |
|---|---|---|---|
| General office (mid-glazed) | 80 – 120 W/m² | 8 – 12 kW | Baseline for open-plan floors on mid-spec glazing. |
| Highly-glazed office / south-facing | 140 – 180 W/m² | 14 – 18 kW | Solar gain dominates — model the glazing, don't rule-of-thumb it. |
| Retail (small shop, standard fit) | 120 – 160 W/m² | 12 – 16 kW | Lighting and occupancy peaks matter more than area. |
| Restaurant / commercial kitchen front-of-house | 200 – 260 W/m² | 20 – 26 kW | Kitchen extract balance must be sized in tandem. |
| Server / comms room | 500 – 2000 W/m² | 50 – 200 kW | Size to IT load in kW, never to floor area. |
| Meeting room (dense occupancy) | 150 – 220 W/m² | 15 – 22 kW | Body-heat and screens push load well above general office. |
| Industrial / warehouse office bay | 60 – 90 W/m² | 6 – 9 kW | Low occupancy density, but check insulation and roof gain. |
Feasibility bands only. AccuTemp installs are always sized from a room-by-room load calc measured against the actual site.
Five things that shift the number by 30%+.
Glazing area, orientation and shading
The single biggest swing after IT load. Frameless south-facing glazing can add 40–80 W/m² of solar gain over the same wall built as mid-spec double-glazing.
Occupancy density
Every person adds ~120 W of sensible heat plus latent moisture. Meeting rooms and call centres routinely hit 5–10× the load per m² of the surrounding open-plan floor.
IT and lighting loads
Server, workstation and A/V loads are all sensible heat and go straight into the room. LED lighting typically adds 8–12 W/m²; halogen/incandescent legacy fit-outs add 25–40 W/m².
Ventilation strategy
Fresh-air rates set by BB101/CIBSE add latent and sensible load the AC has to handle. AHU pre-conditioning changes the picture materially.
Building fabric and roof
Uninsulated roofs, exposed steelwork and thermal bridging push design load up 15–25%. Old warehouse conversions almost always need higher kW/m² than a modern shell.
Related: cost guide, VRF vs split, install timelines, Daikin vs Mitsubishi, HVAC glossary.
Frequently asked questions
- How do I calculate what size air conditioning I need for a commercial space?
- Commercial AC is sized to cooling load in kilowatts, not floor area. A defensible size comes from a room-by-room load calculation covering solar gain, occupancy, IT and lighting, ventilation and fabric losses. A rule-of-thumb 100–150 W/m² office estimate is fine for feasibility, but wrong for install.
- What is a typical cooling load in W per m² for a UK office?
- A mid-glazed general office in the UK typically sits at 80–120 W/m² of cooling load. Highly-glazed or south-facing floors push to 140–180 W/m². A 500 m² general office therefore needs roughly 40–60 kW of installed cooling capacity.
- How is server room AC sized?
- Server and comms rooms are sized directly to the IT load in kW — usually 1.1–1.3 kW of cooling per 1 kW of IT to cover future growth and PSU losses. Floor-area rules do not apply. AccuTemp typically specifies close-control or high-sensible splits with N+1 redundancy.
- Can you oversize AC to be safe?
- No. Oversized AC short-cycles: it hits setpoint fast, cuts out, and never runs long enough to dehumidify or achieve stable temperature. Result — clammy air, high energy use and premature compressor wear. Correct sizing is more efficient than a safety margin.
- How does AccuTemp size systems?
- Every AccuTemp installation is sized on a room-by-room load calculation from measured glazing, occupancy schedule, IT and lighting loads. We do not scale from floor area for install-grade design — floor-area estimates only appear in feasibility numbers before survey.