My bathroom ventilation fan broke up and I am shopping for a new better one. I noticed the newer fans are higher CFM through-put and are quieter, I have narrowed down my choice to this one.
My question is that my condo was built in 1980 so its older, will this fan still do a good job and be quiter? I have read in some product reviews/youtube installation that high CFM fans require bigger ducts. I live in 3 floor condo building. I only have access to the bathroom and nothing outside.
Will this 150 CFM be still a good option for me or I just need to go with the lower ranking basic fan?
The bathroom size is 7 ft by 5 ft. I have no idea of about the ducts size.
Update
I end up asking my condo management and I am told the duct is 6 inches which is great. Now I am gonna go with 150 CFM and I am buying this from Amazon which is way cheaper than others but I worry if this will fit? I took my current one dimensions (from outside) and is 12 by 10.5 inches. The one at amazon shows bigger but I think all new ones will be standard sizes. Should I be worrying about physical dimensions? Thanks!
Best Answer
It's very difficult to determine what type of ducting was used and if that ducting was properly installed or has an obstructions just by the era the building was built. Since the fan is broken you can try removing it to see what size ducting is currently in place.
If your current fan was doing a good job before it broke... meaning you didn't have moisture or mold issues, fogged mirrors, etc... then sticking with the same CFM fan would be a good idea. The new fans should generally be quieter and more energy efficient.
The Home Ventilating Institute recommends a minimum 1 CFM per sq foot in bathrooms smaller than 100 sq ft. That will give you the minimum 8 air changes per hour in a bathroom with standard 8' ceilings with a 50CFM minimum.
For your bathroom you'd need a minimum of 35 CFM. Panasonic makes those WhisperCeiling Fans in various sizes. Larger CFM fans will have a 6" duct and smaller fans have a 4" duct. The WhisperGreen fans use less energy and the smaller sized ones come with the option of connecting to 4" or 6" ducts. Larger CFM fans have a 6" duct. The larger duct size is recommended if the ducting is very long. The ducts create resistance so a larger duct mitigates that. If you have 4" ducts and the ducting isn't very long you should be fine but I don't think you need the 150 CFM fan.
If you can take the old fan out you might be able to tell if the duct is a short straight run if you can see daylight through the duct.