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Air conditioner for an 18 m² room: how many kW?
18 m² is often a larger bedroom with a walk-in wardrobe, a spacious children's room or a study with a lounge area. In a room this size the result depends less on area and more on where the room sits in the building.
When the choice is less obvious
- North-facing room in an apartment block – need 1.7–2.1 kW; quiet operation and steady temperature matter most.
- South-facing room with a large window – need 2.2–2.6 kW; external shading is worth considering.
- Attic under a pitched roof – need 2.5–3.0 kW; roof insulation has the greatest influence here.
When the preliminary range falls between two unit classes, we choose by actual use: if the room is used all day on hot days, the larger class is the safer choice because the inverter modulates output. In the catalogue that means the 2.5 kW (e.g. MSZ-LN25VG) or 3.5 kW (e.g. MSZ-LN35VG, MSZ-AY35VGK) nominal cooling classes.
Preliminary cooling capacity estimate for a 18 m² room
| Window orientation | Load factor | Cooling capacity |
|---|---|---|
| North | 30 W/m³ | 1.7–2.1 kW |
| East | 35 W/m³ | 2.0–2.4 kW |
| South / west | 40 W/m³ | 2.2–2.6 kW |
| South + top floor | 40 W/m³ × 1.15 | 2.5–3.0 kW |
If the air conditioner (an air-to-air heat pump) is also used for heating, a room in energy class C needs a preliminary 0.8–1.2 kW of heating capacity at −23 °C outdoors.
Assumptions: ceiling height 2.7 m, 2 people × 130 W, medium-sized windows, no extra heat-emitting equipment. Formula: Q = A·h·q·fwindows·(1.15 for a top floor) + people·130 W + equipment; range Q…1.2·Q.
Next step
For a more accurate figure, enter the exact ceiling height, window size, number of people and equipment in the air conditioner planner. Before the site visit, prepare photos of the room, a floor plan and a possible outdoor unit location – this shortens coordination and lets the specialist propose the right solution straight away.
This is a preliminary estimate based on the formula of our air conditioner planner; the final capacity and the indoor unit position are confirmed by an EKO2ŠILUMA specialist during a site visit.
FAQ
What should I choose if the figure falls between two classes?
We decide by use, window orientation and whether the unit will heat. An inverter unit also runs at lower output, so a slightly larger class is usually not a problem, whereas an undersized one is.
Does a large window change the capacity much?
Yes. Our tool applies a factor of 1.15 for a large window and 1.3 for panoramic glazing to the base load. The figures in the table are for medium-sized windows.
How much capacity is needed for heating?
For an 18 m² class C room, a preliminary 0.8–1.2 kW at −23 °C. The exact value depends on wall and window insulation.
Suitable equipment
