I have two adjacent bathrooms that I would like to add fans in.

The fans would be located within 5-6 feet of each other and could easily exit the roof at the same point.

If I remember correctly, fans all have a "check valve" or flapper preventing back flow and drafting back into the room.

With that in mind, if they were both plumbed into one vent, it should be no problem right? Turn one fan on, the flap on the other one closes. Turn both on and they both vent.

Good idea or bad? Saves me a little bit of money and one hole in the roof.