VOCs and aircon: what cooling does to a renovated flat

Volatile organic compounds are chemicals that leave a solid or a liquid as gas. The US Environmental Protection Agency uses that definition, and it reaches across thousands of products. Paints, varnishes, solvents, cleaning products and adhesives sit inside it. So do building materials, furnishings and the finishes on new carpentry.

Indoors is where they gather. EPA reports that many of these compounds run consistently higher inside than outside, by up to ten times. Its TEAM study measured about a dozen common organic pollutants at two to five times the outdoor level inside homes. During paint stripping, EPA puts indoor levels as high as a thousand times the outdoor background. It also states that raised levels can persist long after the work stops.

Singapore names its own sources in one place. NEA's advisory on formaldehyde in interior building products lists interior paints, composite wood products, adhesives, and furniture containing composite wood panels. Formaldehyde reaches paint as a preservative that holds back bacteria and fungi. It reaches board and glue as part of the resin.

The older Singapore list runs longer. The 1996 office guidelines put formaldehyde in hundreds of products. Ceiling tiles, particle board, plywood, carpet glues, paint and paper are all named. So are rugs, upholstery and office furniture. A flat fitted out from bare walls meets most of that list in a fortnight.

Timing is what makes a renovation different from ordinary living. Carpentry, flooring, painting and new furniture all arrive in one sealed space across a short window. The sources start together instead of one at a time. Handover day is therefore the strongest the smell will ever be.

Smell ranks those sources badly. The Berkeley National Laboratory work on new houses selected several of its target compounds because they carry low odour thresholds or irritate strongly at small doses. A room can therefore smell heavily of one compound while most of the load is something else. What the nose reports is which molecule is loudest.

The load does fall on its own, and slower than most renovation plans assume. NEA states that newly installed materials typically need time for initial off-gassing to diminish any residual formaldehyde. It then declines to put a period on it. The actual time required to reach acceptable levels varies from case to case, in NEA's own wording.

The measured record explains that caution. Berkeley National Laboratory sampled four new manufactured houses between two and nine and a half months after installation, and seven new site-built houses one to two months after completion. Alpha-pinene, formaldehyde, hexanal and acetic acid led the compounds it found. On time, its finding was blunt. Elevated emission rates for a number of the predominant compounds persisted over a period of at least nine months.

The compounds did not behave alike either. Across that same window, changes in emission rate varied by compound, and only several of them showed a consistent decrease at all. One curve does not describe a room. Different materials release different molecules on different schedules, and a fit-out installs them side by side.

A three-year study puts the turn at about a year. Park and Ikeda monitored new and older homes continuously for three years and published in Indoor Air in 2006. VOC levels in the new homes fell markedly after one year. Formaldehyde and alpha-pinene needed a longer flushing period than the rest. The older homes moved very little across the whole three years.

Neither study was run here. What carries across is the material list, because a Singapore fit-out draws on the same boards, adhesives and coatings. What does not carry is a number. Anyone offering a fixed period after which a flat is clear has gone past what anybody has measured.

NEA's instruction for the heaviest areas is patience and outdoor air. It advises delaying occupancy of heavily renovated areas and extending ventilation for several weeks. That advice is about time and open windows. Running the cooling does not appear in it.

Cooling does one useful thing here, and it surprises most owners. EPA states that heat speeds up the rate at which formaldehyde is released. Humidity plays some part in it too. The same page says a dehumidifier and air conditioning can help reduce formaldehyde emissions, by holding humidity down and the temperature moderate. Cooler, drier material gives off less.

The limit sits in what the machine moves. An aircon recirculates room air, and nothing already released leaves the flat with it. The unit chills that air and hands it straight back. Slowing the emission rate slows the refill. It empties nothing.

A second effect runs the other way and usually wins. A room held properly cold is a room with the windows shut, and shutting them closes the only path that lowers the load. EPA pairs its air conditioning advice with a separate instruction to raise the ventilation rate, especially after new sources come into the home. NEA asks for windows and doors open on opposite sides for cross ventilation, with fans to move the air along. Both bodies treat outdoor air as the operative step.

Comfort and dilution compete for the same room. None of that is a defect in the equipment. Cooling and ventilating were designed as separate jobs, and separate machines do them. The workable arrangement is to decide which one the room needs at a given hour, and to pay the cost of dropping the other.

One quiet exchange does happen at the coil. Cooling condenses water onto cold metal, and room air crosses that wet surface for as long as the unit runs. What has been documented about the compounds collecting there concerns organic acid corrosion of the copper, and not the air quality of the room. No removal rate for a flat has been published.

Two mechanisms get conflated whenever a filter is sold against a smell. Catching a particle means trapping a solid or a droplet on a fibre. Catching a gas means holding a single molecule on a chemical surface. EPA is explicit that its gas-phase technologies are not designed to remove particles, and the reverse holds just as plainly. The panel inside a split unit is built for particles, and the MERV rating that grades such panels answers a different question.

Gas capture runs on a sorbent. EPA describes sorbent media filters as using a material of very high surface area to hold gaseous pollutants, either by physical adsorption or by chemical reaction. Activated carbon is the common choice. Two properties decide how it performs. Every adsorbent has a limited capacity, and each takes up the molecules it has the strongest affinity for while the rest stay in the airstream.

Formaldehyde falls on the wrong side of that preference. EPA states that activated carbon can take up most hydrocarbons, many aldehydes and organic acids, and ozone. It then lists what carbon handles poorly, and low molecular weight aldehydes are on that list, with formaldehyde given as the example. The compound Singapore chose to regulate is the one carbon deals with worst.

Saturation turns a sorbent around. EPA warns that thin sorbent layers can become quickly saturated, and that the filter can then act as a source of previously adsorbed pollutants. Adsorbent media need regular replacement or regeneration to restore the sorbent sites and avoid breakthrough. A carbon layer left past its capacity stops being neutral. It starts giving back.

None of this carries a figure a buyer can check. EPA notes that current test standards rate clean air delivery for particle removal only. Standards for gas-phase removal exist and are not yet widely used or reported. Its review of home studies is blunter again. Work on air cleaners addressing gas-phase pollutants is extremely limited, and consistent reductions have not been demonstrated. A VOC claim printed on a box has no published rating standing behind it.

Singapore has one binding rule aimed at VOCs in a home, and it governs the tin. From 1 January 2026, importing, manufacturing or selling interior paint containing 0.01 percent formaldehyde by weight or more is prohibited here. The Environmental Protection and Management Act is what carries it, with formaldehyde in paint controlled there as a hazardous substance. That is a requirement, and it acts on the product before it ever reaches a wall.

The air itself is covered by an office document older than most flats being renovated today. Guidelines for Good Indoor Air Quality in Office Premises appeared in October 1996. The Institute of Environmental Epidemiology wrote it, inside what was then the Ministry of the Environment. Its stated scope is air-conditioned office premises. A flat was never inside it, and the figures get quoted at flats anyway.

That document splits its numbers across two tables, and the split is the useful part. Formaldehyde appears among guideline maximum concentrations at 0.1 ppm, averaged across eight hours, which the table also states as 120 micrograms in a cubic metre. Volatile organic compounds appear in a separate table headed recommended maximum concentrations, at 3 ppm. The text gives the reason. Guideline maxima were set on known health effects, and recommended maxima on potential ones.

The 3 ppm figure also names its instrument. Its footnote reads total photoionisable compounds, reference to toluene. That describes a photoionisation reading calibrated against one gas, and not a tally of everything present. Two meters set up differently can report different totals from identical air. A TVOC number quoted without its method attached says very little.

The current code and WHO land on the same formaldehyde value, and both are recommendations. NEA cites SS 554:2026 as recommending 0.1 milligrams per cubic metre in the indoor air of certain premises over any 30-minute period. It cites the World Health Organization indoor air quality guideline at that same value, given there as 0.08 ppm. Neither binds a household on its own.

No published document sets a VOC level for a Singapore home. The certification schemes owners get pointed at are voluntary, and their thresholds are not public. The Singapore Green Building Council states plainly that its criteria are not shared publicly. A low-VOC label therefore certifies that a product passed a test whose numbers the buyer cannot read.