Guides
What tonnage your room actually needs
Start at roughly one ton per 120 to 150 square feet in this climate, then adjust up for a west-facing room, large glazing, a top floor under an exposed roof, or several people in it. A 12x14 bedroom is usually 1.5 ton. Oversizing is as bad as undersizing.
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Floor area is the starting point, not the answer
The square-foot rule gets you into the right band and no further. Ceiling height changes the volume being cooled; a room with a high ceiling needs more than the floor area suggests. Everything after that is about how much heat arrives from outside, which varies far more between two same-sized rooms than people expect.
The four adjustments that matter here
Aspect: a west-facing room takes the afternoon sun and needs more. Glazing: a large single-glazed window is a heat source, not a wall. Top floor: a room directly under an exposed roof gains heat all day and often needs a full step up. Occupancy: a bedroom for two and a drawing room for twelve are different loads in the same space.
Why oversizing is a real mistake
An oversized unit reaches the set temperature quickly, stops, and restarts — short cycling. It never runs long enough to pull humidity out of the air, so the room reads cool on the thermostat and feels clammy. It also costs more to buy, more per restart to run, and wears faster. Bigger is not safer.
When to step up rather than add a second unit
A single correctly sized unit almost always beats two undersized ones for cost and running economy. Two units make sense where a space cannot be served by one air path — an L-shaped room, or a hall with a partition. Otherwise, size up and place the indoor unit where its air reaches the whole room.
What size AC do I need for my room?
Is 1 ton enough for a bedroom?
For a modest bedroom on a middle floor with a north or east aspect, often yes. For the same-sized room on the top floor under an exposed roof, or facing west with a large window, 1.5 ton is usually the honest answer. The room's exposure matters more than its floor area once you are near the boundary.
What happens if I buy an AC that is too big?
It short cycles: cools fast, stops, restarts. The room ends up cool but humid because the unit never runs long enough to dehumidify, and the repeated restarts cost more electricity and wear the compressor. It is a genuinely worse outcome than a correctly sized unit, not just a more expensive one.
Does the same rule apply to a shop or an office?
The starting figure does, but the adjustments are bigger. Commercial spaces have more people, more equipment producing heat, doors opening constantly to the street, and often large glazed frontages. A shop needs a proper look rather than a square-foot calculation, and getting it wrong there is more expensive than in a bedroom.
Rather have it done?
AC installation is a sizing decision followed by a plumbing job: tonnage matched to the room, indoor and outdoor units sited for airflow, pipe run kept short and lagged, and the system vacuumed properly before gas is released. Fitting starts at PKR 8,000, and supply-and-fit for a 1.5 ton inverter unit starts near PKR 140,000.
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