Is it really is a duct? If so, there will be too much resistance since they operate at a high speed. The motor will overheat, etc. It needs to vent to an open space, as well have enough replacement air (measured in sq. inches) from somewhere else (read the box to find out how much).

Thanks Homebound...not sure if it's considered a duct. The housing is in the roof of the attic and vents directly outside through a venting area that sits below a cap to keep the rain out. Is this considered a duct? It then pulls air from the attic which spans the length of the house and has a set of louvers (sp?) or vented opening on each end though they are only about 3' X 2'.

Any thoughts given this info would be appreciated.

Thanks again!

This is not a duct. You are simply replacing the fan/motor assembly. The shroud (cap) keeps the weather out but is not a duct. After replacing the assembly make sure the screen surrounding the top of the shroud is in place to keep the critters out. The louvers you are talking about are the gable vents. These are meant to be an exit for air coming into the attic from the sofit vents. They have fallen out of favor with newer construction as ridge vents, which go all the way across the peak of the roof are more eficient. These setups normally provide all the passive ventilation needed for an attic but I suspect a previous owner installed the power vent because of insufficient ventilation. Make sure your soffit vents (located in the flat area underneath your gutters are not blocked.

Thanks busboy...think I'll return the power vent and either find a replacement that is marketed as such or just see how it goes. For all I know, the attic fan may have been inoperable for years. Also, was just talking to someone about ridge cents and will look into this when it's time to replace my roof as it seems like a very logical approach.

Thanks again!