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Red Squirrel 09-12-2010 04:36 PM

oversize duct to reduce static pressure?
Say I want to suck/push air in a duct run, will I get less static pressure if I increase the size of said duct run, and just use a reducer at the fan (so it fits properly)? Or will that make it worse, or make no difference?

nap 09-12-2010 05:39 PM

are you speaking inlet or outlet duct and are you altering the grill size as well?

beenthere 09-12-2010 05:47 PM

IS this a return or a supply.

Red Squirrel 09-12-2010 08:13 PM

This is for an inline bathroom fan, I need to go far with it. The fan would be near the end of the run, so most of it would be sucking action, and not pushing. It requires 4" duct but wondering if going 5" would reduce the static pressure. The inlet would probably be 5" too, one of those round adjustable ones. The fan connections would reduce to 4" then increase back to 5" to push the air out the house through a wall.

beenthere 09-12-2010 09:35 PM

5" will reduce static pressure, and help you get closer tot eh fans rating.

Red Squirrel 09-12-2010 10:12 PM

Good to know, that's what I figured. I also like the idea of using 5" to future proof the system. Maybe later on I'll want a bigger fan, or it breaks down and I can only find 5" ones, so I'll be set. I like the idea of having it in the basement more then the attic anyway, will be easier to service if required.

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