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About this tool
Size an AC for an open living room using a component heat-gain method: walls, roof, glazing, people, lights and air changes.
This calculator sizes an air conditioner for a living room by adding up each heat gain separately instead of using a flat per-square-foot rule: wall and roof conduction as U x A x deltaT with a sol-air uplift of 15 K for a sunlit roof, solar gain through glass as area x solar heat gain factor x shading coefficient, 130 W per seated adult from ASHRAE, installed lighting and equipment watts, and infiltration at 0.335 W per cubic metre per kelvin. A 10% design margin is added and the total is converted at 3,516.85 W per ton of refrigeration. It is built for open halls where a double-height ceiling or a wall of west-facing glass makes the rule of thumb badly wrong.
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Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Shows the watts contributed by walls, roof, glass, people, lights and air changes, and names the biggest one.
Air volume drives the infiltration load, so a 14 ft ceiling is treated differently from an 8 ft one.
West glass is charged at about 480 W/m2 of solar gain versus 110 W/m2 for north glass, before shading.
For a typical 200-250 sq ft Indian living room on a middle floor, 1.5 ton is usually enough; the same room on the top floor with an exposed RCC roof and a large west window commonly needs 2 ton. The deciding factors are roof exposure and glass area, not floor area alone.
Because west-facing glass and a sun-baked roof release stored heat exactly when the room is in use. Peak solar gain through unshaded west glass is around 480 W per square metre, and an uninsulated RCC slab behaves as if outdoor air were roughly 15 C hotter than it actually is, so the load peaks hours after the hottest part of the day.
Yes, though less than the volume increase suggests. Extra height adds exposed wall area and more air to change over — the infiltration term scales directly with room volume at 0.335 W per cubic metre per kelvin — but the roof and floor gains do not change, so going from 10 ft to 14 ft typically adds 10-20%, not 40%.
Yes, measurably. Heavy curtains or venetian blinds cut solar gain through glass to roughly 55% of the unshaded value, and solar-control film or a tinted DGU to about 40%. On a room with 40 sq ft of west glass that is several hundred watts, enough to change the recommended size in a borderline case.
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