Venting multiple exhaust appliances

Q: Can I safely connect my two bathroom exhaust fans and kitchen range hood to a single rooftop vent? Currently all three of these appliances are vented into the attic.

A: As troublesome as it sounds, separate vents offer big advantages. Three fans dumping in to the same outlet will run into a bottleneck that restricts flow and performance. This is especially true with the high volumes of air moved by your range hood. It may be possible to connect the two bathroom exhaust fans into one large roof vent (especially if they're rarely used together), but keep your eye on things. Also, it’s important that the two pipes connect together as closely as possible before the outdoor vent itself. Try this arragnement for a while, then create separate bathroom vents later, if ventilation performance is poor.