AC-02-03-1 -- Depressurization-Induced Backdrafting and Spillage: Assessment of Test Methods

This paper describes test methods for assessment of back-drafting and spillage from vented combustion appliances and compares results from these tests. Tests included short-term measurements under conditions of induced depressurization and continuous monitoring under natural conditions. Data from 42 houses in two geographic areas are reported. The selection of houses for testing was intentionally biased toward ones thought to have a greater propensity for backdrafting. The results indicate that, while study houses were depressurized by an average of 1.9 (±1.3) Pa, none exhibited any significant backdrafting or spillage, based on continuous monitoring of vent pressures and indoor carbon dioxide and carbon monoxide concentrations. Limited cases of positive vent pressure or backdrafting either were caused by an induced draft fan or were transitional spillage events lasting less than a minute. Results of short-term tests, indicating that 10% to 40% of study houses might be spillage-prone, were not supported by continuous monitoring under real-life conditions.