Short, insulated duct runs that vent directly outside allow bath fans to remove the huge load of moisture that showers and baths generate.
Bath fans that work fight mold, and mold is bad.
But wait, there's more: Bath fans that are quiet actually get used; bath fans that are quiet and hard wired to the light are used much more than noisy bath fans that are optional (switched separately).
To sum up, quiet bath fans that are wired directly to the overhead light and vent directly to the outside are pretty much king of the bath fan kingdom.
Back to the example in this episode of Mystery Inspector: Not only is the duct run short, it is nicely insulated with a zip-tie securing the ends of the insulation tube as seen in this close up photo:
Why does insulation on an exhaust duct matter? Because the air that this duct carries is moist air. If that moist warm air becomes cold moist air (like, oh, say, while it travels through ductwork in the attic during the winter), then the air will create puddles in the ductwork because warm air can hold much more moisture than cold air.
Puddles are bad because puddles are made from water, and water's sinister ultimate goal is to turn houses to mush. And that is bad for business. (It also is bad for houses and the people who live in them.)
Attaboy, HVAC guy—give yourself a raise!
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