Can I Vent 2 Bathroom Fans Together

Bathroom code does address the issue of moving odor and moisture laden air from the bathroom to the outside.

Can i vent 2 bathroom fans together. Was replacing bathroom fan 1 and while it was disconnected from its duct pipe the fan in the bathroom 2 was on and. Currently the main bath upstairs has a bath fan that vents through the roof the master bath has only a window and i d like to install a fan near the shower but not in it to provide a little extra light and to exaust the warm moist air when the shower is running. The fans would be located within 5 6 feet of each other and could easily exit the roof at the same point.

When venting a bathroom exhaust fan make sure to vent the air to the outside rather than into your attic where it can cause mold and mildew to form. The 2 fans have their own ducts but just before they vent out the roof their duct pipes are attached to a common duct upside down y which means they vent out the same hole in. Connecting bath exhaust ducts together can result in problems.

A grille in each bathroom attaches to ducts which then fasten to a y connector at the fan. I have two adjacent bathrooms that i would like to add fans in. I am wondering if i can run two exaust fans from two separate bathrooms to only one roof vent with a t or a y.

I felt air coming from bathroom 2 s fan down through the metal duct pipe for venting bathroom 1. The classic example occurs in multifamily units if one tenant is a smoker the tenant next door can smell tobacco smoke that enters the bathroom through the exhaust fan. Surprisingly bathroom fans are not required by some building codes.

But while you can t have two fans with one vent you can make one fan and one vent serve two bathrooms. If i remember correctly fans all have a check valve or flapper preventing back flow and drafting back into the room. This setup requires an in line centrifugal fan mounted in the attic drawing air simultaneously from both bathrooms see photo.

I vote to keep the ducts separate.