I have a small closet that doubles as a laundry room, with a stacked washer and dryer. It's also where I keep my cat's litter box.

It occurred to me that I could probably reduce the odor of the litter box by ventilating the litter box out through the dryer's exhaust duct.

I envision something like this, with an inline exhaust fan forcing air out of the house:

diagram of ventilation proposal

However, I want to avoid pumping the fouled air into the dryer (now that I realize it's been drawing in this air the whole time). Is there a best place to install the tee fitting / fan to avoid this? Would I need to run two exhaust fans?

Cat tax.

  • 3
    You also have the reverse problem - venting hot, wet air from the dryer into the litter box isn't going to help the smell any. Sep 28, 2020 at 15:42
  • @NuclearWang Fair point, but if the exhaust fan is on when the dryer is running, would that prevent airflow in that direction?
    – rgov
    Sep 28, 2020 at 15:43
  • I would try to add some sort of a valve (could be as simple as a homebuilt box with three holes and a flap inside) that would shut off the cat-box airflow when the dryer was running, to prevent the issue @NuclearWang raised... If the valve was designed properly, it might also prevent cat-fumes from entering the dryer when it is off.
    – kgutwin
    Sep 28, 2020 at 15:57
  • 2
    I would not recommend any dual use of the dryer vent. But this hackaday.com/2008/09/16/hack-your-littler-box. Looks like a cool fix.
    – Kris
    Sep 28, 2020 at 18:20
  • Gas or electric dryer? You could wind up euthanizing the beautiful cat...
    – DJohnM
    Sep 29, 2020 at 16:01

1 Answer 1


Sharing ducts in that way usually isn't allowed by code for health, comfort, energy efficiency, and fire reasons, among others. It's not a good idea, as you won't balance venting force without a diverter of some sort, and that means you have to constantly be switching it back and forth for the current need. You're almost guaranteed to forget at times, which creates fairly obvious problems.

Run a second duct along the first. Install a new vent outside with an operational backflow/draft preventer flap.


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