Indoor air quality at home: common questions

Haze days

What PSI level is unhealthy?

A PSI of 101 and above is unhealthy, according to the National Environment Agency (NEA). The index shows how severe the smoke haze is. Check NEA's advisories, which are based on PSI or PM2.5 readings, and cut back on outdoor activity and exertion when readings are high.

How does haze get into a closed flat?

Through gaps. The main pollutant in haze is fine particulate matter, PM2.5, and NEA notes that it enters air-conditioned buildings through the fresh air intake and through openings and gaps, so indoor levels can build up. In a flat, check under the main door and around window frames.

Does an air purifier help on haze days?

Yes, in a closed room. Think of an air purifier, haze or not, as a one-room tool. Portable air cleaners are designed to keep particulate levels low in an enclosed space, says NEA's page on air cleaning devices. Shut a bedroom's windows and door and run it there. If you want to run the aircon as well, see aircon during haze.

Air purifiers

What does CADR tell me?

CADR is the amount of clean air a device can produce for a room. NEA explains that a higher CADR means greater ability to return clean air. If you know both the CADR and your room size, you can make an informed purchase, so measure the bedroom or living area before you shop.

Is there an approved list of air purifiers?

No. NEA does not keep approved lists of air cleaners, and it notes that some devices generate ozone and are not recommended. Ask the supplier for detailed product information, as NEA's air cleaning guidance suggests, including the CADR and whether the unit releases ozone.

Where should a purifier go?

In the room you use most, with its door and windows shut. Portable units are built for an enclosed space, so one in an open-plan living room with the balcony door open has little chance. To see how it compares with the filter in your split unit, read air purifier vs aircon filter.

Ventilation, humidity and indoor air quality in a Singapore home

How do I improve ventilation in an HDB flat?

Open doors and windows, and use fans when you need more air movement. That is what NEA's ventilation guidance suggests for residential homes. Good ventilation in an HDB flat often comes down to cross-flow: open the kitchen window and a bedroom window on the far side of the flat, and leave internal doors open so air can pass through.

When should I keep the windows shut?

During haze, and whenever the air outside smells of smoke, exhaust or a neighbour's renovation dust. Ventilation only helps when the air coming in is cleaner than the air inside. A condo unit facing a busy expressway or a landed home beside a construction site may do better airing out in short bursts at quieter hours.

Why does humidity matter?

Because damp air feeds mould. In a humid climate, a flat that stays shut, with laundry drying indoors and no fan running, gives mould a chance on ceilings, wardrobe backs and bathroom grout. Run the bathroom exhaust after showers, dry clothes near an open window and see the mould FAQ for cleaning and prevention.

Renovation and new furniture fumes

Where do the fumes come from?

Mostly from the new materials. NEA's formaldehyde advisory notes that formaldehyde can be released from interior building products such as composite wood products, adhesives and paints. In a new home, that can include wardrobes, kitchen cabinets, platform beds and freshly painted walls. Our guide to formaldehyde from new furniture covers this in more detail.

How do I choose lower-emission materials?

Look for green labels and ask for test reports. NEA points buyers to green labels from the Singapore Green Building Council (SGBC) and the Singapore Environment Council (SEC), and says buyers may request emission test reports for composite wood panels. Raise this with your interior designer or carpenter before the materials are ordered, not after installation.

Is there a formaldehyde limit for paint?

Yes. Under NEA's rules, interior paints with formaldehyde at or above 0.01% w/w are not allowed. The limit applies to interior paint, so it tells you nothing about the boards in your carpentry. Ask your contractor which panels they plan to use and whether test reports are available.

Aircon and air

How often should I clean the aircon filters?

Clean them whenever you see dust on them, and more often if the unit runs for long hours. Switch the unit off, follow the maker's manual to slide the filters out, rinse them, and let them dry fully before refitting. A clogged filter restricts airflow and makes the room feel stuffier.

What does a musty aircon smell mean?

Often it means mould or damp dirt has built up inside the unit. Clean filters may not fix it, because the smell can come from the coil, drain tray or blower, which are parts for a servicing technician to handle. The aircon smells musty guide explains likely causes and what each fix involves.

Where to go next

Damp often gathers in the bathroom, where steam lingers after every shower. If the ceiling there is spotting or the mirror stays fogged for a long time, read the bathroom exhaust fan guide next. On haze days, check the readings on NEA's haze page before you open up. If you would rather hand a musty aircon to a professional, the directory lists servicing companies with their own published prices. Quotes depend on the job, so describe the smell and how many units you have when you ask.

Questions