Stalled Draft at Furnace Flue

Home Inspector with Hergert Inspection LLC

Stalled Draft at Furnace Flue | Home Inspections Bellevue Seattle Everett

This home located in the Bellevue, Washington area was constructed in the 1950's.

Since that time, it has been extensively remodeled and updated.

mid efficeincy furnace

The newer mid-efficiency furnace has a flue diameter of approximately 5".

It qickly transitions to a connection to the original flue with a diameter of approximately 10".

furnace flue stalled draft

With the furnace activated, the gases from the furnace begin to condensate and drip onto the floor of the mechanical room within a few minutes. There is substantial corrosion at both the flue and furnace.

When changing the efficiency of a furnace or making any other changes to the furnace venting system, consideration must be given to the ability of the flue gases to escape with back drafting into the house or condensing inside the flue as the gases are not as hot as older low efficiency furnaces.

Higher efficiency furnaces extract more of the heat out of the waste gases which can lead to the condensation problem.

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Comments (2)

Randy Ostrander
Lake and Lodge Realty LLC - Big Rapids, MI
Real Estate Broker, Serving Big Rapids and West Central MI

Good morning Kevin. I have been told this can be fixed by adding a liner up the inside of the chimney. Your thoughts?

Sep 14, 2011 05:32 AM
Kevin Hergert
Hergert Inspection LLC - Bellevue, WA

I assume you mean a masonry chimney.

Yes, a liner type pipe could be installed.

You should consult with a heating contractor as there are design guidelines for diameter, elbows, length, .....

Sep 14, 2011 05:43 AM