News Brief

Unvented Gas Heaters Still Gaining Ground

Ten years ago, we expressed concern over the increase in sales of unvented gas heaters (see


Vol. 5, No. 3). At that time, sales totaled about 520,000 units per year. In the intervening decade, sales have risen to over one million units per year.

As the name suggests, these heaters do not require chimneys or other exterior ventilation; rather, they vent directly into the room where they are installed. Proponents of the heaters claim that high combustion efficiency and oxygen depletion sensors (devices that shut off the gas supply if oxygen levels fall below 18%) make the heaters safe when they are properly installed and operated as supplemental heaters. However, most indoor air quality (IAQ) experts argue that even with proper installation and operation, unvented gas heaters release water vapor and such hazardous gases as carbon monoxide and nitrogen dioxide into a home’s living space.

“The chemistry of combustion does not change—if you burn hydrocarbon fuel you get at least water and carbon dioxide, neither of them wanted in excess indoors,” says Michael Apte, Ph.D., of the Indoor Environment Department at Lawrence Berkeley National Laboratory. He notes that even the best-designed products sometimes fail; if one in 1,000 of the roughly five million unvented gas heaters installed to date is out of spec, that’s 5,000 units potentially putting as many as 20,000 family members at risk of exposure to deadly carbon monoxide. “It’s just not prudent to put unvented appliances in our homes,“ he told


A 2004 study in eighteen Australian schools published in the

International Journal of Epidemiology linked unvented gas heaters with increased difficulty breathing, chest tightness, and asthma attacks. But despite these results and the concerns of IAQ experts, unvented gas heaters continue to gain ground.

In our 1996 article, we listed six states that prohibited the residential use of unvented gas heaters. Today, only California still prohibits the appliances, and that prohibition may soon be repealed—the legislation allows the appliances but requires that they be installed as regulated by the state, and the state has not yet written guidelines for installation. Some municipalities across the country do still prohibit the heaters.

Fewer localities prohibit unvented gas heaters now in part because of their inclusion in the codes of the International Code Council (ICC) and the International Association of Plumbing and Mechanical Officials (IAPMO). When the 2006 version of IAMPO’s Unified Mechanical Code goes into effect, both of the United States’ major codes will allow the use of unvented gas heaters.

For more information:

Vent-Free Gas Products Alliance

Gas Appliance Manufacturers Assoc.

Arlington, Virginia

703-525-7060 x240

Published May 3, 2006

Auerbach, R. (2006, May 3). Unvented Gas Heaters Still Gaining Ground. Retrieved from

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