Two bathroom exhaust fans


Old 01-04-08, 06:08 PM
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Two bathroom exhaust fans

I have a first floor bathroom that the vent goes into an unheated/only accessible through a removable panel porch roof. I'm guessing this isn't the best plan as there is nowhere for the vented air to go and the added moisture is probably terrible for the roof and such.

I also have a bathroom on the second floor that has no exhaust vent at all. I would like to add a vent to the second floor as well as run the first floor up that direction.

Is there some way to only have one vent for both fans exiting the house? The bathrooms are directly above and below each other. Or do I have to have two separate vents, one for each fan?

Thanks for your help.

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Old 01-04-08, 07:00 PM
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M1506.2 Recirculation of air. Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors...

If two fans are positively pressurizing exhaust ducts ahead of a common junction to an exterior discharge, then you are recirculating the air from one fan's interior location to the other (less positively pressurized) fan's location.

What you can do is put an in-line fan (like the FanTech products) down-stream of the junction, where it negativitly pressurizes both interior locations, there are both upsides and downsides to doing so.

.. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.
Old 01-04-08, 07:01 PM
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Brad: you should have separate vents for the two fans, due to the volume restrictions of a single exhaust hose. In other words, if both fans were running at the same time the single pipe couldn't handle the volume of air.
Old 01-05-08, 09:22 AM
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Bath fans

Hey Brad,

I get the feeling you really don't want 2 vents for whatever reason.

Depending on your usage patterns, I think you could use one vent for 2 fans, but you would probably have to upsize the vent and vent pipe at the point the 2 fans join. Use a Y pipe to connect the 2 fans, (those are prob 4" outlets) then run a 6" off the Y (of course the 2 legs would be inlets , and the single would be output). I would also install buttterfly dampers on each leg of the fan exhaust, to prevent backflow to the other bathroom, and cut down on drafting.

This would be costlier than 2 vents, if you buy the parts at a big box or hardware store. If you go to a HVAC wholesaler, you will be amazed at how much cheaper the parts would be. Prob less than half the box store cost.

EX: went to a box looking for an 7" adj 90 in galv steel, all they had was cheap aluminum for over $7, the HVAC supplier had just what i wanted, for $2.87!!! wow!

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