Engineering/Air Flow question

A

Atrus

Forum Member
Looking for verification that this should work...

I am in the process of having a new home built. The builder pre-plumbed in (2) 4" vents into the roof soffit for a bathroom fan (one over shower, one over toilet).

I found a fan system I am interested in - a centrifugal fan system in which the system is designed to have (2) 4" inlets that merge to 6" via a Y. The fan itself is 6" inlet, and then a 6" outlet.

Being that I have provisions for (2) 4" outlets already cut into my soffit, I was planning on picking up an additional "Y" and splitting the exhaust side of the fan back into (2) 4" runs instead of (1) 6" run.

That shouldn't be an issue that would hinder the fan's performance or anything, should it?
 
Would need dampers installed on the two 4" intake runs to balance the load. If you did no do that most/possibly all your flow will be on the shortest leg. On the exhaust side it would not matter.
 
ah, good point - I'll try to balance the two intakes. I didn't even think of that.

Intake side will actually be per the mfg's specs, so that should be all good. i was more concerned that I was splitting the single 6" exhaust back into dual 4" exhausts, which isn't to the mfg spec. I didn't think it would matter, but wanted to make sure I wasn't missing anything.
 
You also want a check valve is some point at the outlet of each van if you join them up. You don’t want the moist shower air coming back in the house.

If you are necking down in diameter expect a noisier fan too.
 
04GoaT said:
You also want a check valve is some point at the outlet of each van if you join them up. You don’t want the moist shower air coming back in the house.

If you are necking down in diameter expect a noisier fan too.
Click to expand...

Shouldn't be much of a noise difference as 2 4" conductors have more area which would mean lower velocity then one 6" conductor. Also using insulated flex duct instead of rigid conductors greatly reduces sound levels.

Check valves on both exhausts is a must to keep outside air from entering the house and increasing utility costs.
 
would it help if possible to run "6 outlets up to where the soffits are, then install the exhaust side reducer wye as close to the outside dump area right before the soffit with the 4" out tube?
 
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