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I watched Tom Silva's installation of a bathroom exhaust fan but have questions. Can more than one fan be attached to the ducting & vented out thru side of house? If not, what is the recommended maximum feet for each exhaust fan ducting?
Well , yes it's possible in a single family residence.
However , instead of 2 individual fans a recommendation would be to use an inline fan located in the attic or basement. Then run the ducting (rigid metal is preferred ) " T " ed to the 2 bathrooms. The advantage to this over 2 seperate fans --- the inline is generally more powerful and quieter since the blower is remote mounted.
You would need to wire the switches for the 2 different locations in a 3way switch configuration to be able to control the fan from the different locations.
If you go with individual fans --- again use rigid metal ducting better for air flow and stay away from the cheap white plastic flex ------- you probably can get reasonable performance with a 25 - 30 ft maximum --- the longer the less performance without using larger ducting.
The other issue with the flex ducting are saggs ---- it's not good to have low and high spots for moisture to collect also this adds restriction to the air flow.
Keep the run as straight as possible and keep the hard 90 degree bends to a minimum. The hard 90 's add to resistance of air flow equivelent to roughly 10 feet of ducting.
Also, have the duct gently slope down toward the exit so any moisture will run out instead of siiting inside the duct or running back toward the fan.
Hopefully this helps.:)