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Old 09-07-2007, 09:37 AM   #1
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Venting bathroom through dryer?

I have a main floor bathroom without a vent that I would like to just run down the wall and Y connect to the dryer vent outside (the dryer vent is almost directly below the place I would stick the bathroom vent. This seems like a better way than to put it up through the roof or out through the wall (and thus have to deal with a host of other issues which I'm not really keen on tackling right now). Any problems with just running it down and connecting it to the dryer out? TIA...


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Old 09-07-2007, 01:21 PM   #2
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Yes. If you make a y-connected vent system, your dryer will vent half-outside, and half into the bathroom when the bath fan isn't running.

Your bath fan will vent half into the dryer, and half outside when the dryer isn't running.

Furthermore, you'll blow lint into your bathroom, and possibly carbon monoxide if you have a gas dryer.

It's not a good idea. Use separate vent outlets.


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Old 09-07-2007, 01:50 PM   #3
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Can I not just put those little flap things on the incoming ends of the Y that are shut when no air is blowing, but open when air is blowing?

I had used some previously, for a related issues (where I was venting non-moist air out of a dryer duct along with moist air from the dryer) without much of a problem.

I'm mostly worried that running the vent down a floor would have some unforseen issue....

Thanks for the comments...
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Old 09-08-2007, 11:53 AM   #4
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I was able to do something simular. But my second bathroom is on the same level as the dryer. I did some testing first, to see how it would work out.
I only hooked up one backdraft damper on the dryer side to a Y fitting. Its important to install any backdraft fitting parallel to the flow. I let the dryer run with heat. After 10 minutes, I felt the metal exhaust duct about 6 feet away from the Y fitting, that is connected to the bathroom exhaust and it was warm. This tells me that heat, moisture and possibly some lint will work its way back to the bathroom. Then I added another backdraft damper to the bathroom ductwork in parallel to the flow. This created enough resistance to make all of the dryer flow go out its intended exhaust. When I felt the bathroom duct again, it was cool to the touch.

When you install this, do not use any type of foil or vinyl duct to either the dryer or the bathroom fan. Use smooth metal duct only because foil and vinyl are not as fire resistant as metal duct. Exception: If you were installing an exhaust from a bathroom directly to the outside, then it is permissable. But they also cause more resistance to the flow then smooth metal duct.
They are also not approved for use on dryers.

One last thing: Look for the dampers that have a single flapper valve rather then the 3 or 4 flappers that I see now in the home centers. The single flapper type has less resistance to the flow. You might find these in plumbing shops. Using your finger, check to see if the valve will open completly parallel to the flow. There may be a small bit of plastic actiing as a stopper. Use a file to file it smooth, if you have to. You will probally have to remove the valve from the assembly, but it is easy enough to do.

When your ready to install, make sure you have the damper flow facing towards the exhaust. Mistakes can happen. I put arrow marks on my dampers before I installed them. Install the dampers in a way that will make it easy to remove them in case you need to do future maintainace around them. Then test your installation.
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