On Aug 25, 9:48 am, "RBM" rbm2(remove wrote:
Unless you have local codes preventing it, that is how most bath vents are
done in my area. Do use something other than plastic dryer vent for the
duct. The smoother the better, with the least amount of bends. If you locate
the fan directly over the tub, it'll need GFCI protection

"Nate Nagel" wrote in message

...



one of my projects this fall is to update the wiring upstairs in my house.
I plan on replacing all the ceiling boxes with fan-rated ones, dropping
14/3 switch legs to all the wall boxes for fans, and replacing all wiring
with 14/3 Romex. Also pulling one new 14/2 homerun to provide for two
separate general circuits (original homerun is 14/2 BX so it is grounded
and doesn't need to be redone) and a 12/2 homerun for the bathroom. While
I'm at it I would like to add a ventilation fan in the bathroom to pull
out the condensation while showering (currently using a window mounted
fan) but I am not sure how to vent it.

I don't want to use a conventional stack through the roof as the roof is
aluminum "shingles" and it appears a) hard to work with and b) hard to
walk on without damage. So I was thinking of using a dryer vent type
thing through the side wall of the attic. My question is, is this
acceptable by code, and even if so, are there any drawbacks to doing this?

thanks,

nate

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Some tips about bathroom fans (condensation issues, bends, etc.) he

http://www.askthebuilder.com/546_Bat...tilation.shtml

And stolen without permission from http://tamtech.com/faq.htm#b5

***** Begin Included Text *****

Questions about bathroom fans

What is a reasonable amount of air flow from a bathroom fan?

An installed airflow of about 100 cfm run intermittently should
suffice. Installed performance will be below the label on the box. To
achieve 100 cfm installed, the rating on the box should be 125 to 150
cfm. Too much ventilation is bad when it dries out the house and
wastes too much energy, but for occupant health, too much is better
than too little.



How can I tell if my bathroom fan is working properly?

There is a simple test you can do yourself to determine if your
bathroom fan is working properly. From six inches away, squeeze a
cloud of baby powder from its container toward the intake grille of
the operating exhaust fan. If the fan is working properly, the powder
will be drawn up into the grille. If it goes to the center of the
grille and is blown back into the room, then the fan is blocked; if
the powder simply hangs in the air, the fan is not working at all. Its
just making noise!



Where should I exhaust the air from a ducted bathroom fan?

Always exhaust the air all the way to the outside. Do not dump it into
the attic. Be sure to use insulated duct in unconditioned spaces such
as attics.



My bathroom fan is sometimes very noisy. Why?

Fan noise goes up with increases in pressure. Fan performance will
decrease as the fan ages.



Any other tips for bathroom fan installation and performance?

Sure!

If the bath fan is mounted on the attic floor and has a plastic duct
attachment nozzle, the plastic may soften in the hot attic. So don't
clamp the ducting to tightly or it can deform the nozzle and cause the
backdraft damper not to work.

Often the first turn of the ducting system is the worst turn. Moving
that turn away from the fan and easing it will greatly improve the
performance.

Flex ducting is twice as restrictive to airflow as smooth ducting.
Increasing the diameter of the duct by one inch will reduce the
resistance by about 40%.

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