CAUSES AND CONSEQUENCES OF BACKDRAFTING OF VENTED GAS APPLIANCES

House depressurization occurs when household equipment such as a kitch en or bathroom fan or a fireplace exhausts air from the house and lowe rs the pressure indoors with respect to the outside. The operation of air handlers for forced-air heating or cooling systems also can have a depressurization effect. This depressurization can hinder the natural draft from vented combustion appliances and lead to backdrafting, whi ch in turn can result in combustion gases spilling into the indoor air space. Extensive spillage can cause elevated indoor levels of combusti on products such as carbon dioxide (CO2) and water vapor, as well as c ontaminants such as carbon monoxide (CO) and nitrogen dioxide (NO2). T he focus of this paper is to review studies on depressurization-induce d backdrafting and spillage from gas-fired, draft-hood equipped furnac es and domestic hot water heaters. Qualitative and quantitative techni ques that were used in depressurization and backdrafting studies condu cted in Canada, Europe, and the United States are analyzed. These stud ies have shown that exhaust fans operated simultaneously with fireplac es depressurize houses by 3 to 8 Pa on average. The CO indoor concentr ations due to spillage, as reported in these studies, generally have b een lower than 5 ppm. However, such low CO concentrations do not neces sarily imply that a potential problem associated with backdrafting doe s not exist. Other combustion products, such as NO2, rarely have been measured in prior backdrafting studies. It can be concluded from the l iterature review that causes of house depressurization are well unders tood. However, more comprehensive research is needed to better underst and the frequency, duration, and severity of depressurization-induced spillage in a broad cross section of houses. Efforts in this direction have begun recently in the United States through a workshop to define research issues, pilot studies to develop comprehensive measurement p rotocols, and consensus standard development activities to prepare sta ndardized methods and protocols.