Venting A Bathroom Exhaust Fan

Status
Not open for further replies.
B

barlowc

Joined
Mar 16, 2009
Messages
2,159
Location
Southeast Michigan
I am remodeling our master bathroom. Stripping it down to the studs, new drywall, the works.

It previously did not have an exhaust fan. I have no idea why it was built that way, but always had moisture problems because of it. So I'm going to buy a good, quiet fan that moves air well.

Where should I exhaust it? Is running a conduit up to the roof ridge vent acceptable? That's the way the other bathroom fans are done, one of which is a full bath with bath/shower. Or should I vent it up and directly to the side a couple of feet and out the side of the house?

The latter is as clean looking, but since I'm having the house resided, now is a good time to do it if that's "best".
 
I have one of each type installed in my house. They both work effectively in a single story house. However, for some reason the one venting through the roof became disconnected at the vent and the ducting fell back onto the rafters, thus venting all the moist air into the attic until detected much later. What a mess of soaked insulation, etc. It took an entire summer for the attic to dry out.
 
I think venting it out the side or to the roof are both fine. They probably go to the roof for second floor bathrooms and to the side for first floor bathrooms.

A vent is only required if there is no window. Thats required, does not say a good idea.

In my house they connected the bathroom vent hose to the 4" stack pipe just before it went out the roof. I cannot figure out who thought that was code or a good idea. (Yes, this is the 4" stack pipe connected to all the drains in the house and to the septic).
 
Originally Posted By: Donald
A vent is only required if there is no window. Thats required, does not say a good idea.

So the bathroom has a window, which is probably why they got away with it. But like you said, not a good idea.

This is a second floor bather on a corner of the house. So both the roof's ridge vent and out the side are options. The ridge vent will leave the side of the house looking cleaner and is overall easier to do.
 
Venting to the ridge vent is not a good idea. Either vent it through the roof or out the gable ends (preferred method).

Just sticking the vent pipe near the ridge won't discharge the hot moist air out of the attic. The sheathing will get moist and contribute to mold/rot.

Translation: your other vent is also not correct.

A good home inspector, if you ever sell, should catch it.
 
Last edited:
Originally Posted By: AandPDan
Just sticking the vent pipe near the ridge won't discharge the hot moist air out of the attic. The sheathing will get moist and contribute to mold/rot.

That's kind of what I was wondering about?

The other one originally vented through a can-type roof vent. But when I had the roof replaced, they did ridge venting instead and stuck the exhaust conduit right into the ridge.
 
Since you're having siding done I would get it out the side. You could go through the roof but by the time you figure on having someone out to do it, I'd imagine your siding guy is going to be much cheaper. I would also avoid that roofer as he is too lazy to do things right. You need to change your existing one before you rot the roof sheathing. They just didnt want to cut around the vent and/or didnt want to run for some new parts to trim it out properly.

Also make sure you dont put too much duct on the fan. Most are only rated to push 20' or so.
 
Last edited:
dang... from what y'all are saying, all 4 of the exhaust fans (3.5 baths) in my folks house are plumbed wrong...
the house is a mid 70's manufactured sectional (came in 2 halves), all 4 are hooked to plastic clothes dryer like ducting, that just dump into the open attic....

I've been wondering about a retrofit for a while, as my brothers house has none. (dallas area, mid 70's HUD built house) there are windows in both baths, and for some reason overhead heaters(where you would expect a fan to be. i keep flipping the switch for the fan and then "oh carp" when i start smelling dust/etc. burning off the elements...
 
In my last bathroom re-do, I installed a Panasonic fan/light/heater/night-light combo unit. Super quiet, VERY powerful exhaust fan. I plumbed it with 4" PCV drain pipe to the soffit, used a 90deg elbow to route it down and out and used one of these for the under side of the soffit outside:
PC12031-d.jpg


I used the expensive flexible aluminum tubing for the initial fancy wahoo of a bend I had to do, and used quality aluminum tape for all the joints.
 
Last edited:
Originally Posted By: AandPDan
Venting to the ridge vent is not a good idea. Either vent it through the roof or out the gable ends (preferred method).

Just sticking the vent pipe near the ridge won't discharge the hot moist air out of the attic. The sheathing will get moist and contribute to mold/rot.

Translation: your other vent is also not correct.

A good home inspector, if you ever sell, should catch it.


+1. This is correct

Recently had a remodel, code required it.
 
Last edited:
so question...differences in local building codes in mind, if i was to re-plumb the the fans in my folks place, since 2 of the baths are stacked one atop the other, when i get 'em up the attic, can I run 2 together into one vent, manifold style? or does each fan need it's own external vent?
 
Originally Posted By: earlyre
so question...differences in local building codes in mind, if i was to re-plumb the the fans in my folks place, since 2 of the baths are stacked one atop the other, when i get 'em up the attic, can I run 2 together into one vent, manifold style? or does each fan need it's own external vent?


I have back to back bathrooms on a single story vented together in the attic so only one vent on the roof. Should be OK for you, check code to be sure.
 
I vented ours out a side wall and we haven't had a problem with it in over 10 years. I did make sure the ducting to the outside vent had a slight downward pitch to make sure rainwater could not come into the house through the ducting.
 
I would suggest running it out of the roof (not the roof ridge vent) and installing a flapper roof vent. Ideally, you want the run from the fan to the vent to be dead straight and use non-corregated piping so that the exhaust has the most direct path out of the structure. With the corregated flex pipe, turbulence will cause the humid air to potentially remain in the pipe and condensation may drain back into the fan.

Since the air being exhausted will most likely be warmer than surrounding air and want to rise, I'd strongly advise against routing it to the bottom roof soffet because you will likely have to route it so that at some point it will need to flow down. You've just created a P trap, and you will accumulate all kinds of moisture in there.

The side wall would be the next best option, but again you're asking the air to go in a direction that it normally wouldn't want to go so make sure your fan is strong enough to force it all the way out at an acceptable volume.
 
Last edited:
Vent out the side or into the sofit. My home has 5 done that way. Venting into the attic in my town is a code violation.
 
Last edited:
Originally Posted By: Doog
Vent out the side or into the sofit. My home has 5 done that way. Venting into the attic in my town is a code violation.


Venting into the attic is a bad idea. Moisture and humidity are never good especially in a space that contains insulation and wood.
Cut a hole in the roof and vent it there or vent it to the soffit.
I agree its a code violation and a seriously bad idea.
 
Status
Not open for further replies.

Similar threads

The Critic
Water Temp Issue - Bathroom Shower
Replies
13
Views
822
The Critic
V
Bathroom exhaust fan broken
2 3
Replies
42
Views
3K
Wolf359
spasm3
Ridge vents and gable vents
2
Replies
21
Views
1K
RhondaHonda
69GTX
Fixing a water pipe drip in the wall behind the bathroom sink
Replies
12
Views
1K
tnt_motorsports
C
New bathroom sink advice
Replies
7
Views
608
PimTac
Back
Top