Sleeping with the aircon on all night: what temperature, which mode, and how to keep humidity in range

Not in itself. Sleep needs a room that is cool enough: the Sleep Foundation explains that body temperature falls naturally as you get ready to sleep, and that an overheated bedroom can get in the way of that process, leave you tired and shorten both deep sleep and REM sleep. On a sultry Saigon night the aircon is what holds the room in that range.

Dry skin, a dry throat, a blocked nose and aching muscles mostly come from the way the unit is used, and each cause has a simple adjustment.

No single figure suits every household, and the published recommendations were written for different climates.

Most current units have a Sleep mode. In general it raises the set temperature step by step after you switch it on and slows the fan, so that the room is quieter and not too cold late in the night, when both your body temperature and the temperature outside have dropped. How far it adjusts, and at what point, differs between brands and model years; the manual has the details.

• Choose Cool mode and the temperature you want first, then switch on Sleep mode.
• Set the fan to low or auto, for less noise and no strong draught.
• Angle the louvre up towards the ceiling or away from the bed, never at the face and chest.
• Keep the Off Timer for cool nights. On a hot, humid night, let the unit run until morning at a moderate setting, so the room does not warm up again halfway through.
• With an inverter unit, steady running at a moderate setting usually makes more sense than turning it on and off several times a night.

Dry mode is for air that is damp but not hot. Any aircon dries the room as it cools: water vapour condenses on the indoor coil and leaves through the drain hose. Many models add a dedicated mode, shown as DRY or as a water-drop symbol, which turns the indoor fan slowly so that the unit takes out moisture first and cools only lightly. It suits a cool, rainy night when the room feels damp and hardly needs cooling; how it behaves varies by brand and model year.

Two limits apply. The unit removes moisture only while it is running, and only while its drain is clear: a dusty coil or a blocked drip tray can make it drip, smell and become a place where mould lives. Whether Dry draws less power than Cool varies with the unit, with how warm the room is and with how damp the air is.

The US Environmental Protection Agency (EPA) recommends an indoor relative humidity under 60%, ideally between 30 and 50%, to limit mould. In a tropical climate a bedroom held at about 50–60% is already at much lower risk, and pushing it far lower wastes electricity and can dry the skin and throat. Because the aircon dries as it cools, the reading usually falls during the night while the unit runs.

A small digital hygrometer tells you more than how the air feels; read it early in the morning and after rain as well as at bedtime. Then limit the moisture that gets in.

• Run the bathroom extractor fan while you shower and for a while afterwards, and keep the bathroom door shut so that steam stays out of the bedroom.
• Dry laundry somewhere else. Wet clothes hung in a closed room give their moisture to the air.
• Air the room in dry weather and shut it when it rains: outside air that is damper than the room only adds moisture.

Mould and humidity in Saigon apartments

The signs of a damp room, how to choose a dehumidifier and how to clean mould safely.

Use the aircon in a room where people sleep and a dehumidifier in a room that stays shut. An aircon dries the air only while it is switched on, so running one continuously in an empty guest room or storeroom, just to hold the humidity down, is usually less economical than a dedicated dehumidifier.

That depends less on the hours than on three things: the gap between the temperature you set and the temperature outside, how well the room keeps heat out, and the condition of the unit. Over the same number of hours, a unit set to 27°C in a closed room with the curtains drawn against the sun uses less than one at its lowest setting in a room that leaks air.

• Shut the doors and draw the curtains from the afternoon, so that the room has not stored heat by bedtime.
• Add a ceiling fan or a standing fan on low: you feel cooler at the same setting.
• Keep the filter, the indoor unit and the outdoor unit clean. A dirty unit has to run longer to reach the temperature you set.
• When you buy or replace a unit, choose a capacity that matches the size of the bedroom.

Yes, with more care at both ends of the scale, because these groups are sensitive to heat and to cold. According to the World Health Organization, keeping the home cool enough on hot days is especially important for infants, people over 60 and people with chronic conditions.

For babies, the UK's National Health Service (NHS) notes that overheating raises the risk of sudden infant death syndrome (SIDS). Its advice to parents is to feel the baby's chest or the back of the neck: if the skin is hot or sweaty, take off a layer of clothing or bedding. The room temperatures the NHS recommends for babies were set for a European climate. In a hot, humid one, avoid both extremes: a room that is too warm, and cold air blowing straight onto the child.

For a premature or unwell baby, or an older person with heart or lung disease, ask the treating doctor which temperature and which way of using the aircon are suitable.

A bedroom unit runs for many hours at a stretch in a closed space, so it is the one to keep on schedule. Once damp dust has built up on the indoor coil, on the blower wheel and in the drip tray, the unit tends to smell when it starts, pushes out less air and runs longer to reach the set temperature. For a unit used every night, wash the filter about every two to four weeks and have the unit deep cleaned every three to four months.

Aircon cleaning in Vietnam: how often and what it costs

What a deep clean covers and the fixed price for each type of unit.

Aircon leaking water, icing up or not cooling

What to check when the unit drips or stops cooling.

On an aircon cleaning visit, the Up specialist (an identity-verified UpClean cleaner trained to the Up Standard) covers the bed, the wall and the furniture, cleans the indoor coil, the blower wheel, the drain line and, where it can be reached safely, the outdoor unit, and runs the unit with you before leaving. A wall-mounted unit takes about 45–60 minutes and costs a fixed 250,000 VND at 1–1.5 HP, with the gas pressure measured at no charge. UpClean cleans and does not repair; signs of a fault go into the Up Report, the record with before-and-after photos sent by WhatsApp or Zalo after the visit.

To book, phone or message 0968 726 135 on WhatsApp or Zalo, any day between 7:00 AM and 8:00 PM. Enquiries, quotes and the Up Report can be in English. Many apartment buildings want outside staff registered with building management in advance; the specialist's name and photo, sent to you before the visit, are what they ask for.

Aircon cleaning

The full scope and the price of every unit type.

Home appliance cleaning

For a dehumidifier with a slimy tank or a dusty filter.

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