Yes, in some cases a furnace can still contribute to carbon monoxide (CO) danger even when it’s turned off. Venting problems, blocked flues, or issues with major gas appliances like furnaces, boilers, or gas water heaters can allow carbon monoxide to build up or backdraft into the home.
Because carbon monoxide is odorless and invisible, the most reliable protection is proper carbon monoxide furnace safety, including regular inspections and carbon monoxide detector installation. If a CO alarm sounds or you notice signs of a carbon monoxide leak – such as headaches, dizziness, nausea, or unexplained fatigue – get fresh air immediately and call a professional to inspect your gas appliances.
