Ventilating a bathroom with no exterior walls and no attic access?

VortecJeep

VortecJeep

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Vent in Bathroom on the first floor of our house died. I went to replace it, it was simply venting all that moist air into the space between the the first and second floors. No duct work to get it outside or to the attic. That can’t be good can it?. Is there a good way to ventilate a bathroom with no exterior walls and no immediate access to the attic?
 
VortecJeep said:
Vent in Bathroom on the first floor of our house died. I went to replace it, it was simply venting all that moist air into the space between the the first and second floors. No duct work to get it outside or to the attic. That can’t be good can it?. Is there a good way to ventilate a bathroom with no exterior walls and no immediate access to the attic?
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No, terrible idea, especially if there's a shower or tub involved. Duct it to the exterior.
 
Does it need to be done? Yes.
Is it gonna suck to do it? Absolutely.

Do you have no attic access from anywhere?
 
it is the bathtub/shower our daughters and any guests use.
Only way to get to the attic would be to duct it thru the second story, this bathroom is on the first story. Not going to happen.
Ducting it to outside will require ducting thru a wall, thru the laundry room, and then outside, which is probably the best route. Still not fun, but doable.

It’s a small bathroom. How do you properly size the ductwork? I’m wanting to expel moisture when someone takes a shower. I think I could make it a straight shot with no bends all the way outside by going thru the laundry room.
 
Size the fan CFM for the room volume, and then size the duct based on the duct length and the tables/charts from the fan datasheet (and the available duct fittings on the fan). If it's a small bathroom, it will likely be a small fan with a 3 or 4 inch duct, and given the length you'd likely want to go with 4 inch duct. 4 inch is also the most common size for duct outlets (wall caps, etc) and other accessories too.
Depending on length, PVC or sheet metal is probably the way to go, and make a small slope down toward the wall cap to drain condensation.

Usually would want to plan this according to your joist direction, etc.
 
VortecJeep said:
it is the bathtub/shower our daughters and any guests use.
Only way to get to the attic would be to duct it thru the second story, this bathroom is on the first story. Not going to happen.
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Believe it or not going through the attic is in fact possible. But it depends what is above the bathroom, and a whole lot of luck.
You can run the duct inside a stud space with the right materials. If you are really lucky there is a 2nd floor wall over the bathroom crossing that joist space, AND you can get to the top of that wall from the attic. AND there aren't any electrical lines or horizontal cross braces inside between the studs you pick. Basically a lot of stars have to align for it to work out.

If you run it laterally out a wall, keep in mind you need a good rise to the run and no sags where water will collect.

And never ask yourself... all these years, where has all that moisture been going?
 
Just a thought. Could you use a wall fan and go down into the crawl with your duct leading to a crawl vent? Have to get creative in situations like this.

Also any horizontal runs can build up condensation, try to slope toward exterior if possible.
 
ponykilr said:
Just a thought. Could you use a wall fan and go down into the crawl with your duct leading to a crawl vent? Have to get creative in situations like this.

Also any horizontal runs can build up condensation, try to slope toward exterior if possible.
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I could go down to the crawl space. That would be easier than going thru the wall and laundry room.
 
VortecJeep said:
I could go down to the crawl space. That would be easier than going thru the wall and laundry room.
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Just make sure it doesn’t dump into the crawl. Take it to a vent.
 
I was talking to a friend in England that had a similar problem in his place.
He had some kind of moisture collection system, basically a dehumidifier, that collected it into a drain line.
 
RatLabGuy said:
I was talking to a friend in England that had a similar problem in his place.
He had some kind of moisture collection system, basically a dehumidifier, that collected it into a drain line.
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It isnt a vent, but the right sized dehumidifier would work to rid the room of moisture. Could plumb the drain into the sink/shower drain line?
 
paradisePWoffrd said:
It isnt a vent, but the right sized dehumidifier would work to rid the room of moisture. Could plumb the drain into the sink/shower drain line?
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thats pretty much what his did. You could see the pipe line coming from the ceiling down into a drain line.
What I can't figure is where the exhaust gas goes, the unit will still produce heat and have to move as much air as it pulls in. But since it is "dry" then where you put it is less of an issue.
 
RatLabGuy said:
thats pretty much what his did. You could see the pipe line coming from the ceiling down into a drain line.
What I can't figure is where the exhaust gas goes, the unit will still produce heat and have to move as much air as it pulls in. But since it is "dry" then where you put it is less of an issue.
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If it's a dehu, you could either recirc the dry air into the room or dump out into another room or the hallway.. It doesn't meet code for bathroom venting anyway (it's not a exhaust fan or a window), so do whatever works.
 
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