Exhaust Fan Question

I have a downstairs unit with a bathroom that has no exhaust fan. The bathroom has a false ceiling about 50cm high, can i put an exhaust fan in the ceiling so that the air is extracted into the false ceiling 'cavity' or is this not recommended? I Have no idea and would prefer that rather than having it in the window or wall but just wondering if it can cause any problems..

 

Hi taras and welcome to the forum. If you are down under, I must be up top. As for the fan, it would not be a good idea to vent the moisture from a bathroom into a false ceiling. You need to get that moisture out of the house to avoid mold and wood deterioration. Your house and climate will dictate your options, such as cold climates must be careful about condensation in the exhaust ducts.

good luck
Bud

 

I assume that this is a full bathroom, including a tub or shower. If not, and you just want a fan to "circulate air", I don't think ducting will be necessary. Correct me if I'm wrong but I don't see the harm in venting to empty space.

If moisture is a factor you will definitely want to exhaust the air through ducting and out of the home. If you have a clear shot to an exterior wall, you have an easy out.

As an alternate option to a ceiling exhaust fan. You can use a fan mounted through an exterior wall, forgo ducting altogether.




Bathroom exhaust fans typically have two ratings. The CFM rating is how much Cubic Feet of air per Minuite it can displace. And a Sones level for how loud it is.
The CFM rating should be at least 10% greater than the rooms square-footage. Or a 110 CFM fan for 100 sq.ft. bathroom. Or 80 CFM for a 75 sq.ft. bath. Using this formula, the fan should run for 15 - 30 minutes to adequately exhaust moisture. The higher the CFM the better, meaning the fan wont have to run as long or work as hard increasing the motor lifespan. Lower is ill advised, especially in humid areas.

One Sone is equal to a refrigerator motor. Most budget fans will run between 2.5 and 4 sones. The loudest are 6.5 or so. Once the novelty of new wears off and these fan start to age, they are likely to be described "It sounds like jet taking off in my bathroom!"

Some bath fans have built-in humidity sensors. They automatically turn on when moisture is present and turn off when it is removed. And Timers instead of light switches make it easy to walk away and forget it. These features are especially nice on the ultra-low noise fans.

0.9 Sones is almost inaudible.
The lowest I've seen is rated, "< 0.3 Sones"

 

I see that you are Down Under. This is primarily a North American site. It would be best to check with your local building officials.