How to Determine If a Furnace Vent Pipe Is Blocked

Check for rust on metal furnace flues. Condensation that forms on the inside of furnace flues is corrosive and can cause rust to form on metal flues.

Install carbon monoxide detectors near the outside of the furnace flue. Blocked furnace ventilation systems force carbon monoxide and other combustion byproducts back into the home. Carbon monoxide detectors detect carbon monoxide at low enough concentrations that they can serve as secondary indicators of flue blockage.

Have an HVAC specialist inspect your furnace flue for any blockage or obstruction. No matter how much you check your own furnace vent pipe, there will always be parts of the furnace ventilation system that you will be unable to access. Have an HVAC specialist inspect your furnace vent pipe and flue when you first suspect that they may be blocked.