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Q Our house has two baths that
are close together, but only
one has an exhaust fan. I want to
add a fan in the second bath but
don’t want to cut a hole in the roof.
Can I tie two exhaust ducts together
in the attic and use one exit vent?
Frank Phelps, Rustburg, VA
A Interesting proposal, but it won’t work. You’d often blow air from one bathroom into the other, and local building inspectors wouldn’t approve it. But while you can’t have two fans with one vent, you can make one fan and one vent serve two bathrooms. This setup requires an in-line centrifugal fan mounted in the attic drawing air simultaneously from both bathrooms (see photo). A grille in each bathroom attaches to ducts, which then fasten to a “Y” connector at the fan. A single exhaust exits through the roof (Figure A). You mount a switch in each bathroom. This system is quiet, too. Because the fan is in the attic, you’ll hardly hear it. Look for the special fans (starting at $160) at heating-cooling equipment dealers. We used a system by Continental Fan Manufacturing (800-779-4021; www. continentalfan.com). Fantech makes a similar fan (800-747-1762; www.fantechus.com).
It’s less expensive to simply add a fan in the second bath and vent it separately (Figure B), although that will entail cutting another hole in the siding or roof. If you go this route, consider a fan with a built-in humidity sensor. It detects a rapid increase in humidity, like during a shower, and automatically turns on the fan. The sensor switches off the fan when the humidity drops. The fans with this upgrade aren’t cheap. They cost $150 to $275, but they eliminate the need for a timer switch. Two companies that make the fans are Broan (800-558-1711; www.broan.com) and Panasonic (866-292- 7292; www.panasonic.com).FIGURE A
Both bathrooms are vented by
a single in-line fan that has
one exhaust vent running
through the roof.
FIGURE B
Each bathroom has its own
exhaust fan; each fan vents
separately out the roof.