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Estimate the cooling and heating load of a room from its floor area, ΚΕΝΑΚ climate zone, insulation, floor and orientation.
Shop tables give a single figure per square metre. Floor level, insulation, orientation and climate zone change the required capacity more than floor area does.
The base is 600 BTU/h of cooling and 700 BTU/h of heating per square metre in zone B. The ΚΕΝΑΚ zone (A–D) scales the load; zone D needs up to 35% more heating than zone B.
Multipliers then apply for insulation (pre-1980, 1980–2010, ΚΕΝΑΚ-era), floor position (top floor or pilotis), orientation, and ceiling height relative to 2.70 m.
The result is a ±10% range plus the nearest standard capacity: 9,000, 12,000, 18,000, 24,000, 30,000 or 36,000 BTU/h.
The factors are an engineering model, not an official table. For an open-plan space over 60 m², high ceilings or large glazing, ask an engineer for a study.
A 25 m² living room in zone B, middle floor, 2.70 m ceiling, 1980–2010 insulation, facing west. Cooling: 25 × 600 × 1.10 (insulation) × 1.10 (west) = 18,150 BTU/h, so a 24,000 BTU/h unit. Heating: 25 × 700 × 1.15 × 1.03 = 20,729 BTU/h.
Four climate zones (A warmest to D coldest) assigned by prefecture in ministerial decision ΔΕΠΕΑ/οικ.178581/2017 (Gazette B΄ 2367). Places above 500 m are treated as one zone colder.
Because the factors are conventional values, not measurements of your room. The ±10% range shows how far the estimate can move.
One size up covers more but cycles on and off, dehumidifies less and uses more power. With an inverter unit oversizing is better than undersizing, but not by two sizes.
The page gives both. In zones C and D heating usually needs the larger unit, especially in a home without insulation.
The factors are an engineering model, not an official table. For an open-plan space over 60 m², high ceilings or large glazing, ask an engineer. Heat-pump heating needs the output checked at -5 °C.
Recommended cooling capacity
24,000 BTU/h