Researchers measured formaldehyde for a week in 70 California houses built from 2011 to 2017. Newer homes were far cleaner than homes built a decade earlier, and the bedroom still ran higher than the main room more often than the reverse.
If you are getting indoor air quality testing in a newer house, include the bedroom. In 66 newer California homes, formaldehyde in the main bedroom ran more than 10% higher than in the main living area in 20 of them. The reverse happened in 7.
In these homes, formaldehyde came mainly from indoor sources. Outdoor air supplied about 15% of it, going by the median indoor and outdoor values the authors report.
The study
Brett Singer and colleagues at Lawrence Berkeley National Laboratory, with Francis Offermann of Indoor Environmental Engineering, published the study in Indoor Air in 2020. It was funded by the California Energy Commission and the US Department of Energy; the gas utilities SoCalGas and PG&E funded field staff, and every home had gas appliances.
They measured 70 detached houses built from 2011 to 2017 under California’s building code, which since 2008 has required mechanical ventilation, and under a separate state rule limiting formaldehyde from composite wood products.
Each home was monitored for about a week with windows closed and the whole-house ventilation fan running. Week-long formaldehyde samplers sat in the main living area and in the main bedroom, then went to a lab for analysis.
What they found
In the 66 homes with valid samples in both rooms, the bedroom read more than 10% higher in 20 homes (about 30%) and less than 90% of the main room in 7 homes (about 11%).
The typical home was close to even: the median bedroom-to-main ratio was 1.02, and the middle 80% of homes fell between 0.90 and 1.27. Those percentages of homes are our arithmetic from the paper’s counts.
Continuous monitors pointed the same way, and overnight the bedroom ran even higher than its own weekly average. The authors conclude that for many people, formaldehyde exposure at home “may be higher than indicated by average concentrations at a central indoor site.”
The better news is how much newer homes improved. They averaged 19.8 ppb (median 18.2), against 35.0 ppb (median 29.3) in 108 California homes built from 2002 to 2005. That is 44% lower at the mean and 38% lower at the median. The highest reading in any newer home was 44 ppb; 28% of the older homes were above that.
Every newer home was below the World Health Organization’s indoor guideline of 80 ppb. Every one was above 7 ppb (9 µg/m3), the chronic reference exposure level set by California’s Office of Environmental Health Hazard Assessment, which the authors call the applicable target in California.
Why it happens
This part is our inference, not a finding. Formaldehyde comes off indoor materials continuously, so a room that trades less air with the rest of the house, such as a bedroom with the door shut overnight, would build up more. The authors did not test a cause.
The limits, stated plainly
These are California homes, all with gas appliances, owned by volunteers. Of the participants who answered, 88% reported household income of $100,000 or more. The authors say the sample may not represent new homes in the state.
Windows were kept shut and the fan ran by design. The authors say that setup likely does not reflect normal life, since the whole-house fan was off in 74% of homes when researchers first arrived.
Each home got one week. The bedroom had one sampler, the main room had duplicates. The authors note the passive samplers may have under-read where air was very still. No health outcome was measured, and a level above a long-term reference level is not proof of harm. The typical difference between rooms was small.
The older homes were measured for 24 hours with windows used as normal. The authors say differences in recruitment, sample design and measurement methods between the two studies may have affected the comparison.
What survives: one sample in the living room can understate what someone breathes in bed.
What happens when you fix it
The authors attribute the drop from the older homes to two things: fewer badly under-ventilated homes and lower-emitting materials. In 32 older homes with air exchange under 0.2 per hour, formaldehyde averaged 57 ppb (median 45).
A ventilation fan only helps when it runs. It was running in 26% of homes (18 of 70) at the first visit. Systems with clear labels at the switch were much more likely to be on.
What gets lost in the formaldehyde marketing
Instant formaldehyde readers are sold as a quick answer. Even the research-grade continuous monitor in this study reported anything under 10 ppb only as below its detection limit, until the maker supplied modified software, which the team used in 25 homes. Some of its readings were removed because nitrogen dioxide from gas burners interfered. The study’s main numbers came from week-long samples analyzed in a lab.
What the data supports
- Testing a newer or recently remodeled home: sample the main bedroom as well as the living area, and over a period of time rather than one moment.
- Whole-house ventilation: if your home has it, find the switch, label it, and leave it on. In this study, labeled switches were more often on.
Bottom line
In newer homes, the bedroom often held more formaldehyde than the living room, and every home was above California’s long-term reference level. If you test, test where people sleep.
First step: find the ventilation switch in your home and check that it is on.
illumenair does room-by-room indoor air quality testing in Portland and Vancouver homes.
New construction included. We test the air and explain what we found.
971-363-5626
Sources
Singer BC, Chan WR, Kim YS, Offermann FJ, Walker IS. “Indoor air quality in California homes with code-required mechanical ventilation.” Indoor Air, 2020;30(5):885-899. doi:10.1111/ina.12676.
Offermann FJ. “Ventilation and Indoor Air Quality in New Homes.” CEC-500-2009-085. California Energy Commission and California Air Resources Board, 2009.