OPEN METHOD
The calculation is not a black box.
Every transformation applied by ClimJuste is described here. Manufacturer claims never replace the sources, and no brand funds the result.
Run an estimate1. Room-area baseline
The ENERGY STAR table maps room area to room-air-conditioner capacity using an eight-foot reference ceiling, about 2.44 metres. ClimJuste converts the thresholds to square metres and stops at 65 m².
8–14 m²
5,000 BTU/h
15–23 m²
6,000 BTU/h
24–28 m²
7,000 BTU/h
29–33 m²
8,000 BTU/h
34–37 m²
9,000 BTU/h
38–42 m²
10,000 BTU/h
43–51 m²
12,000 BTU/h
52–65 m²
14,000 BTU/h
2. Published adjustments
Sunlight
Capacity is reduced by 10% for a heavily shaded room and increased by 10% for a very sunny room.
Occupancy
Above two occupants, the estimate adds 600 BTU/h for each additional person.
Kitchen
A kitchen or room used for cooking adds 4,000 BTU/h.
Ceiling height
Above 2.70 m, ClimJuste displays a caution instead of inventing a coefficient absent from the source.
3. Coherence check for a portable unit
ADEME describes portable single-hose units as often less efficient and noisier. When the hose passes through a partly open window, outdoor heat enters again. ClimJuste therefore treats the quality of the seal as a prior decision, not a minor capacity adjustment.
Sealed
The estimate can be considered after passive cooling measures.
Partial
The result remains visible, but the exhaust setup should be improved.
Open
The site withholds the purchase recommendation and hides the range.
4. Passive cooling first
Before starting a unit, ADEME recommends shading exposed openings, keeping windows closed when outdoor air is hotter, ventilating at night, and reducing internal heat gains. When air conditioning is used, its stated minimum setpoint is 26°C.
Read ADEME advice for hot weatherRead ADEME advice for limiting consumptionWhat ClimJuste does not do
The calculator does not know the insulation, thermal mass, thermal bridges, exact glazed area, local climate, or real unit performance. It is not a heat-load calculation and guarantees no temperature.
Last editorial review: 1 September 2026.