Advice on Bathroom vent

18 years ago

I have a small 1/2 bath with no windows, its "land locked" on the 1st floor. I realize I need a fan by code, and its just a good idea. The fan will be mounted in the wall and need to be ducted up through the 2nd floor (about 10 feet) into the attic. It will need to go through a 2 or 3 90deg turns as it goes. I was planning to use a 3" or 4" flexible duct. I figure there will be considerable resistance.

I bought a 50cfm fan but I think there will be so much resistance, that it will make more noise than move air.

My wife hates loud bath fans, and the fan I bought is rated at 4 sones without ducting!

I am now considering using an in-line fan mounted in the attic and controlled by a switch in the bathroom. This should satisfy my noise problems. The smallest fan I can find is rated at 110cfm.

My question, will this be way overkill and create a "draft" in the small bathroom, or do you suppose the resistance will counter that problem, and this is exactly what I need?

TIA

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Comments (7)

lbpod
18 years ago
I can't comment on your fan velocity, but I can tell
you, from experience, that whatever winds up in your
attic is well insulated. The moisture laden air
from your bath will freeze up there and when it warms
up, will leak down your tubing and into whatever you
use as a pick-up, (mine leaked into my ceiling mounted
fan and eventually wrecked the sheet rock.
Jon1270
18 years ago
Agreed; venting into the attic is a very bad idea. You need to get that air all the way to the great outdoors.

Take a look at Panasonic's bathroom fans. I have one, and it's a fine little machine -- not even in the same universe as the big-box store cheapies.

If you want to cut down on resistance, use smooth, solid piping rather than the flexible stuff, and go with the larger diameter.

Here is a link that might be useful: Panasonic fans
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Jon1270
18 years ago
On second thought, if it's just a half bath with no shower or tub, maybe venting into the attic could work? This is not my area of expertise, but the air in this case is more likely to be odor-laden than moisture-laden.
davidandkasie
18 years ago
being that it is only a 1/2 bath venting in the attic would be fine. all 3 1/2 baths at work are doen this way. all you are doing is moving stale/stinky air out of one place and putting it another. there is no high humidity to move.
rjoh878646
18 years ago
I will tell you how they vented the 1/2 bath in my house. They ran the ducting between the floor joists and out the side of the house. Used a dryer flapper to terminate it. If your area between the floor joists is wide open and you don't have that far to go you could easily fish the duct through with an electricians fish tape. They ran mine about 14 ft
jamesbodell
Original Author
18 years ago
How about this. Does placement of the fan in the room matter? I am rethinking this and I may be able to run the vent out the side of the house on the 1st floor, just 12 feet away. I will have to open some ceiling, but it might be a lot easier overall. The 50cfm fan I have should be adequate in this install.

However, to do this, the fan (still wall mount) will be behind the door. The door opens along the wall, and the fan would be located behind the door and blocked when open (like when the room is not being used). Is this a problem?

I was originally going to put it in the wall over the toilet.
rjoh878646
18 years ago
I don't see a problem. It's a stink fan isn't it? It shouldn't matter where its mounted. The door going to be shut when you need it.