Is it bad to turn off the AC in summer?

Switching the AC off before you leave feels like the obvious way to save electricity. Many homeowners do it every morning, and many more do it before a long trip. The problem is what happens inside a closed home while the AC is off: heat builds up, moisture has nowhere to go, and the AC itself sits damp and idle.

An AC does two jobs at once: it cools the air and removes moisture every time air passes over the cold coil. Switch it off and both stop. In a closed home, rising heat and trapped moisture together cause the damage.

DEWA has said that switching off the AC during a long holiday saves the most energy, but that it may result in drawbacks such as fungus formation, bad smells and damage to paint, furniture and electrical equipment because of increased temperature and humidity inside homes. In the same report, Hisham Jaber, founder of The Healthy Home, noted that consistent airflow prevents the moisture build-up that leads to mold and mildew.

Major risks of turning off your AC

1. Heat Build-Up

With the home sealed, heat keeps entering through walls, the roof and glass, and nothing removes it. Furniture, floors and walls absorb it, so the longer the AC is off, the more stored heat the system must remove later.

2. Mold and mildew growth

Mold needs moisture and still air, and a closed home without cooling provides both. The US EPA states that the key to mold control is moisture control and advises keeping indoor humidity between 30% and 60%. Without the AC removing moisture, levels climb past that range and mold starts on walls, ceilings, wardrobes and leather goods. Simple habits for preventing mold help, but none replace steady dehumidification from the AC.

3. Damage to belongings

Trapped heat and moisture warp wooden furniture, lift paint and wallpaper, spoil stored food and leave mold on leather goods. Soft furnishings absorb stale odors that linger long after you return. What happens to furniture in a closed home is often the most expensive part of the damage to put right.

4. AC contamination

An AC coil and drain pan are wet whenever the unit runs. Switch it off and that moisture stays inside with the dust already trapped in the filter and ducts. In a Gulf News report, Dinesh Ramachandran of Rentokil Boecker explained that this residual moisture lingers in ducts, coils and drain pans and can allow mold and bacteria to develop. Mold inside the AC is one of the most common reasons homes smell musty after a break.

5. Higher strain on restart

When a home has heated up fully, the AC has to run at maximum capacity for hours to bring it back down, removing heat from the air, walls and furniture. That long, heavy restart adds wear to the compressor and uses much of the energy you hoped to save. A higher set point avoids the deep heat build-up in the first place.

Recommended settings and best practices

For short outings

Instead of switching off, raise the thermostat to 24 to 26°C on auto mode. The home stays stable and cools back down quickly when you return. DEWA advises 24°C while indoors, and 27°C or switching off when leaving the house. For breaks under an hour, leave it as it is.

Overnight

Use sleep mode or set the thermostat one or two degrees higher. Switching off overnight lets a closed bedroom warm up and gather moisture by early morning.

For long holidays and travel

Set a neutral 26 to 28°C. At that level the AC switches on only now and then, which keeps energy use low while still pulling moisture out of the air. The full checklist for leaving your AC on during vacation includes what to do with the fridge, water heater and drains.

Pre trip prep

1. Close all curtains and blackout blinds to block direct sunlight
2. Empty the fridge of perishables, and clear bins and food waste
3. Leave wardrobe, cupboard and internal doors slightly open so air can circulate
4. Clean the AC filters and check the condensate drain is clear. DEWA recommends cleaning filters monthly during the busiest cooling months
5. Pour water into every drain so the traps do not dry out
6. Ask someone to check the home every week or two

A quick AC inspection before travel catches blocked drains and weak components before they fail while nobody is home.

Does leaving the AC on cost more

Some, but far less than repairing mold damage. According to DEWA, raising the thermostat by 1°C can cut electricity consumption by up to 5%, and a home held at 26 to 28°C runs the AC in short cycles rather than continuously. DEWA also recommends programmable thermostats or smart AC controls to avoid cooling an empty home, and its Away Mode feature in the DEWA app lets you monitor consumption while you travel. Smart thermostat control lets you raise the set point remotely and bring it down a few hours before you land.

When switching off makes sense

• Rooms nobody uses. With split units, switch off the unit in an empty room and keep that door closed.
• A home that stays occupied and ventilated, where moisture is controlled in other ways.

For continuous use, the questions around running an AC constantly are about maintenance rather than risk.

When you get back

1. Open windows for 15 to 20 minutes and run exhaust fans.
2. Check wardrobes, bathrooms and behind furniture for damp or mold.
3. Clean the AC filters and run water through every tap and drain.

If the AC blows a musty smell after you return, professional AC cleaning removes the mold and bacteria from the coil, drain pan and grilles, so the first cool air you breathe is clean.

Sources and references

1. Khaleej Times: DEWA statement on keeping the AC on during long holidays
2. DEWA: Advice on AC Temperature When Leaving Home (2021)
3. Gulf News: Why turning off your AC when you are away could be a mistake
4. US EPA: A Brief Guide to Mold, Moisture and Your Home