How to Choose an Air Cooler: The Five Things That Actually Decide It

An air cooler is an evaporative device. It draws air through wet pads, water evaporates, and evaporation takes heat out of the air. The entire effect depends on the air being dry enough to absorb more water vapour — which means the drier your summer, the better a cooler works.

In practice: below about 45% relative humidity, which describes Delhi, Jaipur, Ahmedabad, Nagpur, Hyderabad and much of north and central India through April to June, a correctly sized cooler makes a real difference. Between 45% and 60% it helps, but modestly. Above 60% the cooling effect largely collapses and what you notice instead is a damper room. In Mumbai, Chennai, Kochi, Kolkata and coastal Gujarat, and essentially everywhere once the monsoon arrives, a cooler is the wrong purchase.

This is the single most common reason people are disappointed by a cooler, and it has nothing to do with the brand or the price they paid.

This is the second thing listings rarely say, and it surprises people who are used to air conditioners. An AC recirculates air in a sealed room. A cooler does the opposite: it pushes cooled, humidified air into the room, and that air has to leave. If it cannot, humidity inside the room rises until evaporation stops — and the cooler is still running, still consuming water and electricity, and no longer cooling.

So a cooler needs a window or door open opposite it for cross ventilation. A windowless internal room is not a room a cooler will work in. This also means the sizing method is different: coolers are sized on air changes per hour, not on a sealed-room heat load, which is why our calculator asks about ventilation before it asks about anything else.

Every listing leads with tank capacity, and most buyers therefore treat litres as a proxy for power. It is not. A 90 litre tank runs longer between refills than a 50 litre one. It does not move more air.

What decides whether the far corner of the room cools is air delivery in cubic metres per hour, air throw, and the floor area the manufacturer rates the unit for. The method: floor area in sq ft × ceiling height in ft × air changes per hour ÷ 35.315 gives the m³/hr you need. Use 20 air changes for a room with one window open, 30 for a properly cross-ventilated home room, 40 for a shop or hall, 60 for a factory.

The awkward truth is that these figures are published far less consistently than tank size. Of the 260 coolers verified on this site, 54 state an air-delivery figure and 66 state a rated floor area. Where a brand publishes neither, that is recorded on the model rather than filled in with an estimate — and it is a reason to prefer a competitor that does publish.

The pads are where the actual cooling happens, and they are the specification buyers most often never look at. There are three types in the Indian market.

Honeycomb (cellulose) is the one to buy. It holds more water per unit of airflow than the alternatives, resists clogging in hard water, typically lasts two to three seasons and can be rinsed rather than replaced. 241 of the 260 coolers verified here use it.

Aspen is shredded wood fibre held in a mesh. It cools well in very dry heat but compacts and needs replacing more often. Wood wool (khus) is the cheapest and the one most likely to hold odour once it has been left damp — it is a false economy on anything you intend to keep for more than a season.

• Personal — compact, for one person or a room up to roughly 200 sq ft. Verified models here start at ₹4,900. It will not cool a hall, whatever the tank says.
• Desert — the large, high-airflow format for dry heat and big rooms. Biggest tanks, longest throw, highest water use. The mainstream choice in north and central India.
• Tower — narrow footprint, better looking in a living room, smaller tank and generally shorter throw. Buy it when floor space, not cooling power, is the binding constraint.
• Window — mounts in a window opening and draws fresh air from outside, which is exactly what evaporative cooling wants. Frees up floor space entirely; needs a spare window.
• Industrial and commercial — sized on air changes across a floor rather than degrees in a bedroom. Tanks to 750 litres. The right category for a shop, warehouse, workshop or hall.

This is where coolers genuinely win, though the advantage is routinely overstated. The median rated power across the 260 coolers here is 190 W. At ₹8 a unit and ten hours a day through a 180-day season that is about ₹2,736, against roughly ₹17,280 for a 1.5 ton inverter air conditioner run the same hours — close to a sixth, not the 'free cooling' some listings imply. Add a modest amount for water.

India published its first BEE star-labelling programme for evaporative coolers in May 2025, voluntary from July 2025 with a mandatory phase from July 2026. Star grades are therefore arriving, but almost no listing we read states one yet — so for now, compare rated input power in watts, which every maker publishes.