The Formaldehyde Threat

March 01, 2014
March/April 2014
A version of this article appears in the March/April 2014 issue of Home Energy Magazine.
Click here to read more articles about Indoor Air Quality

[Editor's Note: 2014 marks Home Energy magazine's 30th year in print.  To celebrate, we are rerunning a selection of older articles with comments and updates of how the topic has changed—or stayed the same.]

The buildup of formaldehyde vapors in some tightly sealed houses can cause headaches and irritation. There are several actions a homeowner can take to alleviate the problem.

A few years ago, workers in a newly installed office trailer at Lawrence Berkeley Laboratory began to complain of headaches and dizziness. Some of the workers also noticed a peculiar, stale odor in the office. The symptoms were alleviated by opening the doors and windows to increase the ventilation; however, the problem was bad enough that scientists installed devices to monitor the levels of formaldehyde inside the trailer. It turned out that the formaldehyde levels were just below the ASHRAE indoor standard of 0.09 parts per million (ppm). (This level, equivalent to 120 μg/m3, is recommended by ASHRAE in “Ventilation for Acceptable Indoor Air Quality,” standard 62-198l. The level they recommend is derived from the Community Air Quality Guide of the American Industrial Hygiene Association.)

The original layout of this formaldehyde article from 1984.

Table 1. Distribution of Formaldehyde Levels in Mobile Homes Sampled in Washington State

Worker complaints eventually became less frequent. Today, the building materials that contain formaldehyde have aged. Formaldehyde levels in the trailer are now much lower, and the occupants no longer complain of headaches.

Stories similar to the one above have occurred in hundreds of office trailers, mobile homes, and tightly sealed residences around the country. High indoor formaldehyde levels present a real problem, because formaldehyde trapped in houses can cause headaches and irritate the eyes and throat. The type of dwelling most likely to have formaldehyde concentrations high enough to cause irritation is a new, tightly-sealed mobile home, but many types of houses may experience the problem.

Roughly 20% of the population is adversely affected by formaldehyde concentrations of 0.25 ppm, and some hypersensitive individuals react to concentrations at or below the 0.09 limit, which is only a voluntary guideline.

There are several factors determining formaldehyde levels in residences. They are:

  • the amount of new particle board and plywood products in the house;

  • the presence of urea-formaldehyde (UF) foam insulation;

  • the ventilation rate;

  • the age of the formaldehyde-containing products in the house; and

  • the temperature and humidity of the house.

Sources of Formaldehyde

Indoor formaldehyde vapors generally come from three types of sources:

  • particleboard and plywood products,

  • urea-formaldehyde (UF) foam insulation, and

  • the combustion of gases.

Formaldehyde is incorporated into both plywood and particleboard products as a urea-formaldehyde (UF) resin. Plywood is made by gluing together several sheets of thin wood with the resin. Particleboard is made by saturating small pieces of wood shavings with the resin and pressing them together. UF resins can make up as much as 10% of the dry weight of the finished boards. Unfortunately, formaldehyde from UF resins can migrate into the air. Phenol-formaldehyde resins, which are used in exterior plywoods (for greater moisture resistance), do not release formaldehyde as readily as UF resins; however, UF resins are generally used for indoor wood products because of their lower cost. Since particleboard and plywood are used in almost all buildings, these products are the major sources of indoor formaldehyde.

UF foams were developed in 1933 in Germany and were first used as insulation in the 1960s. As interest in energy conservation picked up in the 1970s, the use of UF foams for insulating homes increased sharply. UF foam became a popular means of retrofitting because it can be injected directly into the walls of a house. The foam is prepared by mixing UF resin with a foaming agent and a catalyst; pressurized air is forced into the mixture, creating a foam, which dries completely within a few days. If the foam is improperly mixed (for example, too much formaldehyde in the resin) or improperly installed (for example, injected during very humid, warm weather), it may outgas over time and become a major source of indoor formaldehyde.

Some formaldehyde results from the combustion process in gas and kerosene heaters. These sources are not usually significant. A study conducted at the Lawrence Berkeley Laboratory in 1983 concluded that formaldehyde emissions from these sources [unvented combustion appliances] “are not likely to be a problem...unless the appliance is poorly tuned or malfunctioning.”

Factors Affecting Formaldehyde Levels

Mobile homes provide a case study of how a combination of factors can result in dangerously high indoor formaldehyde concentrations. Mobile homes are prone to high formaldehyde levels for three reasons. First and foremost, they contain a significant amount of plywood and particleboard products. Thus there is the potential for a lot of formaldehyde to be released into the indoor air. Second, the low ventilation rates in mobile homes mean that formaldehyde vapors which escape from UF resin products can build up to high levels. While a low ventilation rate alone does not cause high formaldehyde levels, it will certainly make matters worse. Third, compared to conventional houses, most mobile homes have low ceilings and small rooms. This means that formaldehyde from the walls and ceilings outgasses into a smaller air volume. Thus, new mobile homes often have higher formaldehyde levels than new houses built out of comparable materials.

Other factors contribute to high indoor formaldehyde levels. As mentioned previously, if UF insulation is installed under very warm, humid conditions, formaldehyde will be more readily released. High temperatures and high relative humidity will contribute to formaldehyde outgassing even after the insulation is installed. In one study a UF foam panel was tested at 23°C, 33°C, and 40°C; thirteen times more formaldehyde, on average, was released from the panel at 400C than at 23°C.

The age of the formaldehyde-containing materials in a house makes a big difference. Over time, formaldehyde levels will decrease to nonproblematic levels. The outgassing process may take from one or two to several years, depending on the size of the house and the amount of formaldehyde products.

Measured Formaldehyde Levels

Studies of the formaldehyde levels in residences have shown that if air change rates are less than 0.3 air changes per hour (ACH), indoor formaldehyde concentrations are often above the ASHRAE guideline. It is difficult to gauge the extent of the formaldehyde problem because the data are sketchy. For example, as of 1982 the Consumer Products Safety Commission had received over 3,000 formaldehyde-related complaints. The majority of these involved UF foam insulation; the remainder involved plywood, particleboard, paneling, and other UF resin products. However, this is probably only the tip of the iceberg, since many homeowners may not associate minor health problems (headache, dizziness, sore throat) with the formaldehyde levels in their homes. Sampling programs in a few states have shown that the formaldehyde problem is quite widespread and that mobile homes are very likely to have high formaldehyde levels. The data in Table 1 provide an example: 80 percent of the mobile homes tested in a Washington State study had formaldehyde levels greater than 0.20 ppm.

Other construction types can have a formaldehyde problem; the gas can build up to high levels in tightly sealed houses that contain a lot of formaldehyde products. In a new, energy-efficient house in Mission Viejo, California, the concentration of formaldehyde rose threefold after furniture was moved into the house (from 0.07 to 0.19 ppm). With the occupants inside the house, the formaldehyde levels rose slightly higher, probably due to the use of gas appliances such as a stove or heater. As would be expected, formaldehyde concentrations decreased dramatically when the windows were opened.

Comments in 2014:

Over the last 30 years, we’ve learned a lot about the health effects of formaldehyde. When scientific studies documented the negative health effects of exposure to formaldehyde in the 1980s, it was still widely used as a binder in particleboard, plywood, and fiberglass insulation, and as a treatment in fabrics and other building products. Since then numerous scientific bodies, including the World Health Organization’s International Agency on the Research of Cancer and the state of California’s Office of Environmental Health Hazard Assessment (OEHHA), have determined that it meets the criteria for a known carcinogen.

In 2000 the state of California developed the Section 01350 “VOC Emissions Assessment” standard protocol to limit individual VOC emissions, including from formaldehyde, from interior finish products to safe levels. By 2002 the Collaborative for High Performance Schools had adopted this standard for evaluating carpets in its green-school program. LEED now applies the Section 01350 standard to virtually all interior finishes.

The California Air Resources Board established new regulations in 2007 to regulate formaldehyde emissions from composite-wood products, including particleboard, medium-density fiberboard, and interior plywood. A serious air quality crisis in trailers purchased by HUD for people made homeless by Hurricane Katrina provided pressure to improve HUD’s regulations and to develop national guidelines based on the California action.

The composite-wood industry is responding rapidly to the California and national regulations. Some existing products have been reformulated to reduce emissions from formaldehyde binders. Other new products, like a soy-based binder, are made without using formaldehyde. And market pressure has increased on the insulation industry to stop using formaldehyde in binders for fiberglass batts.

—Tom Lent
Tom Lent is the policy director for the Healthy Building Network, in Berkeley, California.


Homeowners suspecting high formaldehyde levels can send away to one of several companies for a passive monitor. If the problem is severe, professional help may be required (for example, to remove particleboard or UF foam insulation); however, some simple control procedures are described below.

One of the most effective control techniques is to increase the ventilation by opening doors and windows or to use mechanical ventilation. This is impractical in cold climates, where increasing the ventilation would drastically increase heating bills. In such cases an air-to-air heat exchanger can be installed to recover heat that would otherwise be simply exhausted outside. The heat exchanger has two blowers: one expels inside air, while the other draws in outside air. In the process most of the heat of the outgoing room air is transferred to the cooler incoming air. A typical heat exchanger that can be installed in a window costs around $350.

Air filters are often mentioned in the literature as a practical way of reducing indoor formaldehyde levels; however, industry claims of an air-filtering device that can remove formaldehyde from the air have yet to be substantiated.

Treating particleboard or plywood products with vapor barriers can greatly reduce formaldehyde outgassing. Painting and wallpapering can also lower formaldehyde concentrations. Special vapor barrier paints have been developed that also work well. Vinyl carpet and vinyl wallpaper seem to be the most effective vapor barriers.

Neutralizing formaldehyde vapors with ammonia is another possible control technique. This can be accomplished by either injecting the ammonia into the wall cavities or evaporating an ammonia solution in the affected living space. This technique is best left to professionals because it has some serious drawbacks: the ammonia can discolor some wood finishes and may adversely affect property and belongings.

Long-term Solutions: Improved Manufacturing Techniques

Since formaldehyde products (particleboard and plywood) are essential building materials, the formaldehyde problem will be with us for some time. The steps outlined above are simple and effective abatement techniques for the house; however, long-term solutions to the formaldehyde problem will have to deal with the source strength of formaldehyde in building materials. The makers of particleboard and plywood products are currently developing techniques that will reduce the amount of formaldehyde escaping from these products into the air. The techniques include lowering the ratio of formaldehyde to urea in the resin, partial substitution of other glues for UF resins, and pressing particleboard to closer thickness specifications in order to minimize the need to sand the finished board (sanding increases formaldehyde emissions from particleboard). No single preferred method has surfaced, yet these factory control techniques represent the best long-term means of eliminating the formaldehyde threat.

Peter du Pont was Home Energy's first managing editor. He is now an energy consultant for Nexant in Southeast Asia.

  • 1
  • NEXT
  • LAST
Click here to view this article on a single page.
© Home Energy Magazine 2023, all rights reserved. For permission to reprint, please send an e-mail to
Discuss this article in the HVAC group on Home Energy Pros!

Add a new article comment!

Enter your comments in the box below:

(Please note that all comments are subject to review prior to posting.)


While we will do our best to monitor all comments and blog posts for accuracy and relevancy, Home Energy is not responsible for content posted by our readers or third parties. Home Energy reserves the right to edit or remove comments or blog posts that do not meet our community guidelines.

Related Articles
SPONSORED CONTENT What is Home Performance? Learn about the largest association dedicated to home performance and weatherization contractors. Learn more! Watch Video