BACKGROUND: There is increasing attention on the effects of residential fossil fuel combustion, particularly the use of natural gas or oil, on indoor air quality. Given the prevalent use of natural gas in Canadian homes, understanding its influence on indoor air quality is important. OBJECTIVE: This study investigated associations between indoor levels of nitrogen dioxide (NO METHODS: Using mixed models and general linear models, we evaluated the associations between potential sources and pollutant concentrations, conducting both city-specific and pooled analyses for winter and summer seasons. RESULTS: Our findings indicated that gas stoves, present in 24% of the homes, were significantly associated with increased indoor NO IMPACT: This study enhances understanding of the association between fossil fuel combustion and indoor air quality in predominantly detached homes. It highlights differences in pollutant levels between homes with gas and electric cooking, which can inform advice on cooking practices to reduce emissions in homes.