wall mounted exhaust fan

Hi. I need to replace the fan in our powder room. It is extremely noisy. The fan is mounted in the wall and uses a 4" duct. I am trying to find a quiet wall fan but have not had any luck. The panasonic wall whisper is for a 8" duct so it wont work, correct? Is it true that I cant mount a ceiling fan in the wall? Our handyman said it doesnt matter but that is not what I read on the panasonic website.

Does anyone know of a wall mounted fan that is pretty quiet, using the existing duct work in my house? Thanks for any advice.

Wall fans are generally classified as "utility" fans, and as such are not avbailable in the ultra quiet. I suspect that your fan with the 4" discharge may actually be a ceiling fan, mounted in the wall, Does it discharge directly horizontal, or out sideways into a duct?

Fans designed for ceiling mount...the bearing design is not necessarily suitable for horizontal mounting, and thus the life will be shorter.

Two ways to move the same amount of air...small hole, fast, or bigger hole, slower. The slower you can run the fan, the quieter it can be. Quality matters, too, as there are some fan blade designs that are more expensive to make, and motors, too. I'm assuming the wall is an outside wall? If it isn't covered by a covenant (i.e., restrictions on what exterior changes can be made), you could change the hole to accomodate the Panasonic. Not sure what else is out there. The magic thing to watch is the sone value - the lower it is, the quieter it is. Compare apples to apples.

Thank you for your help. I will have to see how the duct runs. I know it vents through the side of our house. Maybe since I said the most important thing to me was the quietnest, our handyman suggested a ceiling mounted fan. Thanks again. I love this forum.