Can I vent 2 bathrooms via 1 roof jack? Pls read.


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Old 02-11-19, 07:18 AM
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Can I vent 2 bathrooms via 1 roof jack? Pls read.

Ok, I read in many places I shouldn't, but always due to reasons not present in my current situation.

I have 2 side by side bathroom with modern expensive automatic exhaust fan on the ceiling. After I bought the house I went into the attic and noticed the ducts were simply dropped there, with no connection to any roof or side vent. Absurd.

I know people say 2 individual vents would be better... But both exhaust have dampers to avoid backdraft in themselves, noise is not a problem (they are quiet) and the installation would be a simple upside down "Y" in my attic, quite short (5 feet from base to roof)...

I simply dont see why this would not work... Am I missing anything?

Thanks
 
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Old 02-11-19, 08:07 PM
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If you don't currently have a roof jack..... just install two of them.

My opinion......
Using a Y pipe is a comprise. Will it work...... meh. Will both fans perform properly..... maybe.
 
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Old 02-19-19, 09:11 AM
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OK... But just so I understand... What are the potential problems with the Y pipe? I just dont see why it would be a problem... Thanks
 
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Old 02-19-19, 09:21 AM
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If you and your wife share a 16 oz drink by using 2 straws, do you both get 16 oz? Or if a garden hose has a splitter, do you get more water from each hose when they are both turned on at the same time?

Similarly, each bath van is rated for a certain amount of CFM... (volume of air)... and a Y on a bath fan will "work" in that it will vent air... just not as efficiently as if each one had a dedicated duct. Only so much air can be vented out a 4" pipe at a time. When you simply put a Y on, the air speed remains the same, and the outlet size remains the same, yet you are trying to move twice the air (when both are on at the same time, that is) so each bath fan might only be working at 50% efficiency if they are both using the same exhaust duct. And even when you are only using one fan at a time, it's possible for backpressure to cause a "little" air to be exhausted back out the unused bath fan.

Inline fans are used in situations where 2 fans are used on the same duct... they are installed after the Y and speed the movement of air so that the CFM at each fan is not reduced.
 
 

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