Two Fans One Duct

There may also be bypass ductwork around the second fan if only one fan is run for a period of time.

Two fans one duct.

Of course there is some issue with the volume of air from 2 ducts going into 1 duct but i m sure some engineer has figured that part out. But while you can t have two fans with one vent you can make one fan and one vent serve two bathrooms. It would then clear both. 2 bathroooms lead to the fan then exit through one pipe out the roof.

You may wish to move up to the next size of duct. This setup requires an in line centrifugal fan mounted in the attic drawing air simultaneously from both bathrooms see photo. If you try to combine them into a common duct it will bring with it a number of problems including an unbalanced system with positive negative air pressures which play havoc with the fan motors and could cause motor failure. You d often blow air from one bathroom into the other and local building inspectors wouldn t approve it.

2 backdraft dampers one on each leg at the y to stop the backflow of noxious gases from one fan on to the other off. The problem as i understand it is that if both fans are using the same duct and are both running at the same time the fans will be less efficient and more noisy because it will be like installing a fan with a smaller duct that it was rated for. You should not put more than one fan into a common duct each fan should have its own duct run to atmosphere. Rather than two cheap axial fans into one duct outlet how about two ducts into a more powerful centrifugal fan which is a bit more expensive but has a lot more oomph.