i understand that the maximum size hole I can put through a 9" floor joist is 3". But if I add a 5" booster fan would it be possible to retain proper air flow and route this duct through the joist using a 5" to 3" reducer?

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    I'd look at splitting the duct into two 3" pipes as it passes through the joist. The added complexity and expense of a booster is to be avoided. – isherwood Jan 23 at 14:40
  • I'm confused about what I'm seeing up there. Why is one joist lower than the other? What are the boards at the left end? – isherwood Jan 23 at 14:44
  • Both joists are the same height, there are just boards scabbed onto the bottom of one. – Christopher Jan 23 at 15:39
  • Wouldn't you need more than two 3" pipes to keep the volume consistent? – Kevin McKenzie Jan 23 at 16:44

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