We had professionally installed kitchen exhaust vent, venting outside. We had 300cfm and we were having smell issue in the house even after venting outside. We replaced the fan with 900 cfm and still having issue with smell in the house. Our new fan will run for few minutes and then shuts off. We called the guy back who installed our 900 cfm fan and he said there is leaking from the pipe that was installed for venting out.

What kind of pipe should we use? Why we are still having smell in the house when we cook even with 900 cfm fan?

  • 1
    stink moves at the speed of sound, no fan moves air that fast.
    – Jasen
    Commented Feb 25, 2021 at 7:55
  • If there's a leak in the exhaust piping and it's leaking back into the house, guess where your smells are going. Seems like your only option is to fix the leaking pipe.
    – FreeMan
    Commented Feb 25, 2021 at 12:42

1 Answer 1


If the fan works against the natural wind flow, a part of the kitchen exhaust air may re- enter the building.

Natural flow is from West to East on the northern Hemisphere most of the time, but could be changed by mountains, buildings, weather or geographic anomalies.

In other words, the exhaust end should be on the Lee side of the building.

Very important with kitchen exhaust fans is the interaction with furnaces, gas ovens, fire places or other combustion units in the building. The kitchen fan could produce a relatively strong pressure decrease, which pulls the poisonous exhaust gas into the building, if the chimney effect is too weak.

That is why an interlock mechanism is mandatory in some jurisdictions.

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