Reduce AC Use at Home: Keep a Kerala House Cooler

A Kerala house can feel like an oven by late afternoon, and the easy answer is to switch on the AC and leave it running. You can reduce AC use at home without giving up comfort, mostly by keeping heat out in the day, letting cooler air in at night and leaning on your ceiling fans. This guide uses tip sheets from the Energy Management Centre Kerala to show what to do with windows, fans and the AC itself, with safety steps for each.

Key takeaways for a cooler house

• Shade the east and west windows, and close the curtains on windows that get direct sun.
• On hot days, keep the house closed during the day and let air in at night instead.
• Pair the AC with a ceiling fan, which lets you stay comfortable on a milder setting.
• Do not air-condition rooms nobody is using.
• Clean the AC air filter every month while you are using the AC regularly.

For fans, the Energy Management Centre (EMC) Kerala, under the state's Department of Power, tested a ceiling fan with two kinds of speed regulator. At lower speeds, the fan drew less power with an electronic regulator than with the old resistance type. At full speed, both drew the same.

Why does a house heat up from the inside?

Part of the heat in a room comes from inside the house itself. The EMC Kerala cooling tip sheet calls this internal heat gain: appliances, electronic devices and lights all give off heat that adds up. It lists the biggest sources as stoves and ovens, clothes dryers, water heaters, old incandescent bulbs, television sets, electric irons and computers.

• Lights: switch them off when not in use. The sheet suggests replacing old incandescent bulbs, which it rates as a major heat source.
• Cooking: on hot days it suggests more cold meals, using the microwave more, and baking at night.
• Television and computer: switch them off when not in use. The sheet suggests plugging the TV into a power strip and turning that off too.
• Washing clothes: use the cold or warm settings, and run the machine at night.

A Kerala house adds its own heat on top of this. Afternoon sun beats on a concrete terrace and soaks into the walls, so the rooms upstairs stay warm long after sunset. In many homes, heat from the kitchen also drifts into the living area.

Moving the heavy, flexible jobs to a better time of day helps on two fronts: the house stays cooler in the evening, and if you have rooftop solar, more of those jobs run on your own power. See the best time to use appliances with solar.

How to keep sun and heat out during the day

Shade the east and west windows. On hot days, keep the house closed tight during the day so that hot, humid air stays out, and put off heat-making jobs until evening. Close the curtains, and the windows, on any south- or west-facing window that gets direct sunlight. Planting shade trees around the house is also on its list.

The same EMC Kerala tip sheet compares a few window measures. Where it gives a figure, it is shown here exactly as printed.

• Outside shading stops heat before it reaches the glass. A bamboo or cane blind on the western verandah is a good start.
• Keep curtains on the sunny side drawn from late morning, and open them again once the sun has moved off that wall.
• If you plant trees for shade and you have rooftop solar, think about where their shadow will fall in a few years. Read what to check when shade appears on solar panels.
• On a flat terrace, keep the surface in good repair. If panels are mounted there, follow how to find and fix a roof leak around solar mounting before any coating work.

When should you open the windows at night?

The tip sheet says ventilation gets rid of unwanted heat if the incoming air is at 25°C or lower, which is why it works best at night and on cooler days. A window fan should sit on the downwind side of the house, facing out. Keep a window open in each room, and leave the interior doors open so air can move through.

The EMC Kerala fan fact sheet makes a related point. Keeping windows open for natural air circulation lets you run the fan less, or at a lower speed. It also warns that a fan running at full speed in a closed room will heat the room up, so warm indoor air should always have a way out.

• Open up the house once the air outside feels cooler than inside, not simply at sunset.
• Open windows on opposite sides of the house so the breeze has a path in and a path out.
• When rain is driving in during the monsoon, close the windows on that side and keep the switches and sockets nearby dry.

Ceiling fans first: regulator, size and speed

This table comes from the EMC Kerala test of a ceiling fan with a 1400 mm sweep. At each regulator step the fan ran at the same speed with either regulator; only the power drawn changed.

EMC Kerala also set out to disprove the belief that a resistance regulator uses the same power at every speed: in its table, power falls at lower steps with that type too, just less. On average, the sheet reports 27% lower energy use with an electronic regulator than with a resistance one when the fan runs below full speed. It advises good-quality, step-type electronic regulators and energy-efficient fans.

The same fact sheet also advises choosing the right size of fan for the room. Its table, for homes:

• If the regulator gets warm or hums, or the fan wobbles, have a licensed electrician look at it. Do not open the switchboard yourself.
• When you buy a new fan or regulator, compare the star labels of models of the same size. How to read a BEE star label explains each line.
• At night, a mosquito net lets you sleep with the fan on a lower step, or with the window open, as the fan sheet itself suggests.

How to reduce AC use at home without losing comfort

The tip sheet's main advice on the AC itself is to pair it with a ceiling fan. The sheet gives the standard comfort range for light summer clothing as 22°C to 25°C, and suggests keeping the thermostat at 25°C or higher when ceiling fans are on. Do not air-condition rooms that nobody is using, and turn the AC off when you leave for more than an hour.

Humidity matters as much as heat in Kerala. The sheet advises keeping moisture sources out of the house, and not running a dehumidifier while the AC is on, because the dehumidifier adds to the cooling load and makes the AC work harder.

A Kerala example. In a two-storey house in Thrissur, the upstairs bedroom AC used to be switched on soon after dinner and run on a very cold setting all night. The family now draws the west curtains in the afternoon, opens the upstairs windows and ventilators for a while after dark, and runs the ceiling fan on a low step alongside the AC on a milder setting. The AC runs only in the room where people sleep.

Units used by the AC land on the same meter as the rest of the house. To see how a bigger bill period is charged, read how KSEB tariff slabs and fixed charges work.

Keeping the AC in good shape, and buying the right one

For upkeep, the sheet says to clean the AC's air filter every month during the cooling season, because normal dust build-up can reduce air flow by 1 percent a week. It also says that shading the outdoor part of the unit, where possible, can raise its efficiency by 5 to 10 percent, and that the AC should be properly maintained.

When it is time for a new AC, the sheet's buying advice is short. Make sure it is properly sized and matched to the room, with help from an energy auditor or an AC contractor. Buy a BEE star labelled model. In a hot, humid climate, check that it removes humidity well; the sheet says models with variable or multi-speed blowers are generally best. The label lines, and the default setting rule for new ACs, are covered in our guide to BEE star ratings.

• Switch the AC off and isolate it as the user manual describes before you slide out the filter. Wash it gently and let it dry fully before refitting.
• Leave everything behind the front panel, the gas lines and the outdoor unit to the authorised service technician.
• Never climb onto a wet or sloped roof or a sunshade to reach the outdoor unit. Ask the technician to move it if it is hard to reach safely.
• Water dripping inside, ice on the pipes, a burning smell or a breaker that keeps tripping all need a technician or a licensed electrician, not a home fix.

Checklist: cooler rooms this week

• Note which windows and walls take the strongest afternoon sun, and shade the worst of them.
• Agree on a routine: close up in the morning, open up after dark when the air outside is cooler.
• Look at your fan regulators and plan to replace old resistance ones with good electronic ones through an electrician.
• Clean the AC filter and book a service if it has not had one this season.
• Use the AC only in occupied rooms, with the door shut and the fan on.
• If you have rooftop solar, look at how evening use shows up as import in your KSEB solar bill, line by line.

Frequently Asked Questions

Official Sources and Accuracy Note

• 01Natural House Cooling Tips (Energy Management Centre Kerala energy conservation tip sheet, keralaenergy.gov.in)
  Takeaways list: 'Tricks for keeping the house cool' items 1, 2, 4 and 12 (shade east/west windows, keep the house closed by day and ventilate at night, ceiling fans and thermostat at 25 C or higher, no cooling of unused rooms) and the A/C tip to clean the filter every month in the cooling season.
  govt source · opened 2026-10-25
• 02Technical Fact Sheet: Ceiling Fan Speed Control (Energy Management Centre Kerala, EMC/EED/PUB/0107, keralaenergy.gov.in)
  Takeaway paragraph: the fact sheet summary that an electronic regulator reduces fan power at reduced speed compared with a conventional resistance regulator, with both equal at full speed (step 5, 73.5 W).
  govt source · opened 2026-10-25