Carbon monoxide measurements in homes

Carbon monoxide is one of the indoor air contaminants in homes that causes the most concern among energy efficiency programs. Programs that perform energy upgrades to homes spend substantial effort evaluating carbon monoxide hazards. Furnaces, boilers, water heaters, and ovens/ranges are common sources of carbon monoxide in the indoor environment. The current article presents results of carbon monoxide measurements from two studies that looked at homes that underwent energy efficiency upgrades as part of the U.S. Department of Energy's low-income Weatherization Assistance Program. In the first study, carbon monoxide was measured in the flues of furnaces, boilers, and water heaters, in the exhaust of ovens/ranges, and in the indoor ambient air. Measurements of the appliance combustion gases were done once while at the site, and indoor air measurements were done using dataloggers recording for about a month before and after weatherization. In the second study the focus was only on measured indoor ambient air, also with measurements using dataloggers for about 1 week. The results show that most appliances have carbon monoxide levels within allowable standards, though some are elevated. Regarding indoor ambient air, less than 5% of homes have persistent levels (i.e., for more than 10% of the time) of carbon monoxide of 5 ppm or higher. However, elevated peak levels above 9 ppm are much more common, with about 20%–30% of units in both studies reached 9–10 ppm at least once within a week-long test period. These results show that elevated indoor ambient carbon monoxide is a highly episodic phenomenon, and, therefore, not well addressed by whole-home ventilation. Further, the data suggest that it is the cooking appliances that are most subject to producing short-term elevations of carbon monoxide. The current article also includes a comparison of carbon monoxide before and after retrofits.