Air Conditioning Room Sizing Calculator

Get a fast, guided estimate of the right unit size for your room

Room Details

Job / Room reference

Room type

Number of occupants (typical)

Room length (m)

Room width (m)

Ceiling height (m)

Fabric & Glazing

Exposed external wall area (m²)

Area of walls facing outside, excluding windows

Wall / building insulation standard

Room is under a roof (top floor / loft room)

Adds roof heat gain

Window / glazing area (m²)

Glazing type

Main glazing orientation

Internal Gains

Additional equipment load (W)

PC+monitor ~150W, server rack ~500-1500W. Commercial catering: use nameplate ratings.

Ventilation rate (air changes/hour)

Auto-filled from room type — override if needed

Sizing safety margin

Advanced: design temperatures

External design temperature (°C)

UK summer peak design condition

Internal target temperature (°C)

Default ΔT = 6K. Sol-air uplift +5K walls / +15K roof applied automatically.

Recommended unit size

Calculated load:

Load component	Sensible (W)	Latent (W)

Standard tier bands: 2.0 / 2.5 / 3.5 / 5.0 / 6.0 / 7.1 / 8.0 / 9.0 / 10.0 kW (single split range). Above ~10kW typically needs multi-split/ducted — refer for design.

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