As more and more heating systems are upgraded to higher efficient systems, the water heater vent, which share a common flue/vent/chimney with the heating unit, is overlooked. Heating contractors, plumbers and local building officials seem to ignore or are not concerned whether the water heater will vent properly. This failure to address the venting has resulted in dangerous conditions. Backdrafting has become one of the most dangerous conditions followed by rust and corrosion.

All natural draft water heaters are required to have a riser of 12″ (this is a small section of vent piping directly above the draft hood), per vent pipe manufacturers (the photo shows an incorrect installation).


All water heater vent piping is required to be 4″ in diameter no matter if the heating unit is an 80% or 90% type system. When problems are seen the vent pipe is typically 3″ diameter.

One problem seen is extensive rusting/leakage due to the moisture in natural gas, which is very corrosive. If flue gases cannot vent the moisture up and out of the venting system, moisture will condense on the vent piping walls and deteriorate the piping.

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Backdrafting is when the flue gases cannot vent upward due to a cold flue or 45/90 degree bends in the vent connector and backs out the draft hood (this is very dangerous if carbon monoxide is present in the flue gases). The riser allows the flue gases more time to heat up the flue to get an upward draft going (photo shows melted plastic due to backdrafting).


Homeowners should check there water heater venting system at least twice a year for problems.

Rich Roshak is a licensed New Jersey home and building inspector and has construction experience dating back to 1974. He is the owner of AmeriSpec Inspection Services in Somerset, NJ and can be reached at 87-921-3062 or rich@njamerispec.com.


NJ Amerispec inspects homes and offers Radon Testing (continuous monitor), Warranty Inspections, New Construction Inspections, Chimney Inspections (level 1 and 2), Consulting Services and Infrared Energy Scans in New Jersey including Somerset, Bergen, Middlesex, Monmouth, Hunterdon, Passaic, Morris, Essex, Burlington, Union and Ocean Counties.