I realize this is an ancient topic, but it is a classic problem. Ceiling exhaust fans have to be cleaned or they will spin and spin without moving air. I decided to tackle mine today. We leave it running 24/7 because the bedroom suite it is in has no other source of fresh air. The fan brings in air from the rest of the house. I found the brand name (Hampton Bay) on the grille and Googled it. I know it came from Home Depot and was bigger than I needed. I'm pretty sure it was the 140 CFM model for our 100 square foot bathroom. Found the installation instruction manual online and found that I only needed to remove 3 screws to lower the fan/motor out of the housing. I was about to remove the housing and all, so glad I found the instructions. To clean the fan I used a stiff bristled brush, wooden shishkabob skewer, a serrated PLASTIC knife, and of course a vacuum cleaner. Using metal scrapers or a wire brush would damage the plastic blades. Here's a better picture of the job half done. You can see the partially cleaned blades on the left and the gunk on the bottom. On the right side you can see what I was up against. This fan was installed a year ago. The people contributing to this topic who suggested using the brush attachment on a vacuum, moist cloth, or compressed air clearly have never cleaned a squirrel cage type exhaust fan. The moist air combined with dust forms a solid plaque on the fan edges that has to be cracked and then scraped off. The serrated parts of the plastic knife worked great for breaking the solidified muck off the blades. Unfortunately it seems like hundreds of blades to clean. I didn't count them, but you can see there are a lot. Every blade needs individual cleaning. I broke the surface muck off and then used the stiff brush to help scrape off the rest. That didn't work completely, so I had to hit it with both the pointed and blunt ends of the wooden stick. In the end I went over each blade about 3 times from the front and back sides. Here is the after picture. It is not perfectly clean, but getting the dirt off around the top is especially hard. That is the bottom of the blade when installed but the top when cleaning it. The whole project took 3 hours and was very tedious. Removing the squirrel cage from the motor and soaking it first might have made it easier to clean. Might try that next time. Another idea is to run just the squirrel cage through dishwasher on the top rack.

Fantech is just covering their bases and providing a good service at the same time. They want the ducts insulated for the condensation issues and insulated flex duct is smooth (relatively) on the inside so that takes care of the static pressure loss associated with the corrugated types. Their fans' design don't necessitate use of flex insulated duct, it's simply a good choice from a cost / performance / ease of install perspective. Rigid smooth wall pipe is more durable and has less static pressure loss than flex duct, but is sometimes more difficult to install ESPECIALLY if it is insulated properly after the fact by hand. We often use a hybrid arrangement with Fantech and other remote blowers - ins/flex duct from the grille to the motor and then rigid duct to the outside. The flex has install advantages in the confined spaces often left in shower stall ceilings. The spaces we run the ducting in are almost always conditioned so the ducting itself being insulated is not really an issue. This is not the case in attics or crawlspaces that are not insulated or conditioned - so proper design a detailing for each project is necessary.

brickeyee-a remote mounted fan appears to be what I'm looking for. Do you know of any nice ones? Our kitchen is not very big (11' x 12'), so a modest size vent fan would do, something very quiet to draw out smoke, etc. It gets cold here in the winter, so we need an exterior vent that would prevent back draft. oldhousegal-those laurelhurst fans are beautiful, but we already have an antique grill.

I don't know what your climate is but, in a cold winter climate those direct-thru-the-wall fans are unpleasant to operate in the winter because you open a large damper to blow the air out. I looked at a house with one and they also had it covered on the inside with plastic during the winter. These have become very uncommon with only a few manufacturers making replacements for them and I think there is a reason for that. It would be better than nothing but I would plan on replacing it with a conventional range hood at some point.