Combustion safety tests are an important part of a performance check-up or a maintenance call for homes with combustion appliances that rely on gravity draft exhaust. This includes furnaces and water heaters that burn gas, propane, or oil and have open flues with a risk of combustion gas spillage when other fans are operating in the home (e.g., kitchen and bathroom fans or clothes dryers). This test helps diagnose whether these appliances are operating safely by checking if there is adequate air for all the combustion appliances present, making sure the appliances are safely exhausting emissions up the flue or chimney, and verifying that no emissions are pulled back into the home even if all of the exhaust fans in the home were operating at the same time.