AC Size Calculator

Cooling load · unit sizing

Room

Sizes in metres

Length (m)Width (m)Height (m)

Room typeMain glazing faces

sets the sun exposure for youSun exposure

Gains

Optional — sharpen the estimate

PeopleDefault 3Kit in the roomAnything else (W)South glass (m²)Sun-facing glazing

Heat-loss calculator

Coming soon

Room-by-room fabric heat loss for heat pump sizing — U-values, design ΔT, flow-temp and emitter checks.

How this sizing works — and when to distrust it

The estimate starts from room volume at trade rule-of-thumb watts per cubic metre for the room type, then adds the loads a volume number can't see: people (about 120 W each), equipment heat, and sun through south-facing glass (about 150 W per square metre). Orientation sets the sun factor for you; the biggest single cause of undersized units in the field is glazing gains nobody counted.

When one indoor unit can't cover the load, it plans a multi-split rather than pretending — two to five heads, ranked by least oversizing, because a unit sized for the hottest day of the year runs badly for the other 360. For critical or genuinely complex spaces, run a full heat-gain calculation instead of a quick-size.