I have two dryers (one gas, one electric) and their exhaust pipes are merged with a "Y" to a common exterior exhaust. I'd like to keep it that way to minimize cuts through the wall (and eventually I may get rid of the old electric dryer).

The new gas dryer is 15 feet away from the wall, the old one is close to it (and to the "Y").

Question: there's a bit of back draft when the gas dryer is working. I can smell it when I'm around that old electric dryer. Can I install some sort of backdraft preventer? Is there such a thing?

3 Answers 3


@Peter: I think you answered your own question in your comment to ChrisF. What you want is an "inline draft blocker." And you'll want two, one for each dryer. Here are a few on Amazon:




  • Thanks! Then the question is: would that blocker block the air too much given that my gas dryer pipe is 15 ft long (max allowed per code, given the two right angles).
    – Peter Q
    May 8, 2011 at 1:44
  • Keep everything clean and I'm guessing you'll be fine. It's amazing how much lint can build up in a dryer vent line over the years, and that will do more to block the air than a draft blocker.
    – BMitch
    May 8, 2011 at 11:10
  • 1
    I would worry a little bit about lint building up on these devices and becoming a fire hazard. I would install them in a place where it's easy to remove them for cleaning and for cleaning the ducts. You're not going to be able to clean the ducts with those flappers in the line. Jun 28, 2015 at 19:47

Don't put anything in the path of the outlet of a dryer, the reason is lint will catch on it and build up which can lead to a fire. What you want to do is join the two lines so that the airflow is like a Y so that air from each dryer will flow outward to a single pipe. You can find the fittings in the HVAC area of stores. Air likes to take the easiest path and going with the flow of a Y fitting makes it where the air doesn't want to go through the Y then back towards the other dryer. The Y fitting needs to be as close to the exit as possible.

In a commercial laundromat where multiple gas dryers exhaust into one much larger duct there are "check-vales" in the form of metal dampers on each machine that prevent above-described backflow. They don't always work well.

Of course residential style machines don't have one.

As a reminder, clothes dryers should NEVER be exhausted into the ductwork of any other type of appliance.

Stove/cooker exhaust hood: GREASE and LINT combined is a big fire and safety hazard.

Hot water heater/furnace boiler. JUST DON'T. The dryer will force poisonous gasses back into the living space by way of these appliances which add their own poisonous byproduct gasses.

Bathroom exhaust fans: Can't run both a the same time due to excessive volume of air.

In my opinion just install another separate vent. Relatively easiest and safest thing to do.


I don't know whether you can get them to fit inside an exhaust pipe, but you can get one-way grilles/vents for the outlet.

These have a series of flaps that can swing one way only - outwards - so when the hot air is blowing out they flip up, but they get forced closed when blown from the outside.

If you could fit something like that between each dryer and the "Y" then this would solve your problem.

This is a picture of what I mean:

tumble dryer vent kit

Obviously this won't work as the grille wont fit in line, but it shows the flaps.


Not the answer you're looking for? Browse other questions tagged or ask your own question.