We bought a 350 CFM range hood with a 7in vent. Our installer ran a 4in diameter flexible aluminum foil air duct horizontally through the floor joists to outside. We are now told the 4in pipe is too small. The duct diameter should be at least 6in. Is this correct?

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    Yes, your installer was incompetent on several levels. Range hoods should not be vented with flexible duct, AND it's too small. A grease fire in a foil duct becomes a house fire in very short order. If you care to bother, you can find applicable code and drag the incompetent into (small claims, presumably) court. – Ecnerwal May 19 at 11:24
  • I agree with Ecnerwal that is like putting a 351 in a Ford pinto all that power and no place to go but it just might start a fire. I believe the installer if a contractor could be liable but legal issues are off topic. – Ed Beal May 19 at 14:58
  • Makes sense. I would have thought that air can be compressed, though? – user2233706 May 19 at 21:18

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