Two bathrooms, one vent outlet?
billingsdave
| Posted in Mechanicals on
I’m building a cabin using ICFs for the external walls and want to keep wall penetrations to a minimum. What is the most economical way to vent a half bath on the ground floor and a 3/4 bath in the basement using just one vent opening through the exterior wall?
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With ICFs your cabin will be relatively airtight, so you'll need a whole-house plan for ventilation. The best approach is to use an HRV or ERV, which should be configured to draw stale air from both bathrooms. Unfortunately, this setup has two wall penetrations (one for exhaust and one for intake) but there's no way around that. Relying on an exhaust-only strategy is potentially troublesome, but read the archived articles here on GBA and make an informed choice; maybe it's an acceptable solution for a cabin that's only seasonally occupied.
David,
The least expensive approach would probably be to purchase an inline exhaust fan, and to connect the exhaust ducts from both bathrooms to the fan with a Y fitting. The simplest way to control the fan would be with wall-mounted toggle switches; in this case, you would wire the two switches as 3-way switches.
The disadvantage is that whenever the fan is used, it is exhausting air from both bathrooms. But it sounds like you are asking about an economical approach, not a sophisticated approach.
I know it's frowned upon, but why couldn't a guy put regular bathroom fans in each bath with dampers in the lines to prevent back flow from the other bath, run them both to a Y fitting and out of the building?
David,
The problem occurs when both fans are on at the same time. They have to be able to overcome the pressure the other is exerting. To to that you need to increase the size of the common duct. At that point the question becomes: Are two small penetrations any more of a problem than one bigger one?
Gotcha. An additional question: The main floor fan is in a half bath and is basically a "fart sucker." The basement fan is where the shower (and water vapor) would be. To minimize possible condensation in the line, should I make the short downhill run from the basement vent to the outside vent and just loop the main floor vent down inside an interior wall?
David,
Your question is hard to understand. But the principle is: If possible, the exhaust duct should slope toward the exterior termination.
That isn't always possible, of course. But remember that condensation isn't usually a problem unless the duct is located in a cold attic.
Thanks, Martin. Sorry for the confusing question. What I meant to ask was if it would be preferable to place the exterior termination of the vent ducting and inline fan on a short run from the basement bath vent (with shower and more moisture) and bring the vent duct from the main floor powder room down inside an interior wall to the Y fitting in the vent ducting.
David,
Q. "Is it preferable to place the exterior termination of the vent ducting and inline fan on a short run from the basement bath vent (with shower and more moisture) and bring the vent duct from the main floor powder room down inside an interior wall to the Y fitting in the vent ducting?"
A. I guess the answer is "yes" -- although for an accurate answer, I'd need to ask, "Compared to what?"