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4 Inch Dryer Duct in 2x4 Wall

Hello all,
I am a new member here.
I am in the process of overhauling my dryer venting. I have a 2x4 wall behind my dryer. I am thinking of using one of the dryer boxes for 2x4 walls but I am concerned about compressing the 4 inch duct inbetween the drywall to form a slight oval and the heat it will see since it will be in contact. Is this a firehazard? Do I need to use a special drywall?

Background: The current duct in the wall is 3x4 rectangle and has not been in use. The dryer was vented into the garage instead by the previous owner. It appears to be custom made and fits nicely in the wall (1963 home). I don't know how to connect to it with out it looking cheesey, hence switching to the 4 inch round. At the top of it, it appears the builders used a 5 inch to 4 inch reducer to adapt from the rectangular duct to the 4 inch round that completes the last few feet before going thru the roof.
Appreciate any help.

Re: 4 Inch Dryer Duct in 2x4 Wall

I'm not sure what it is that you are doing. Are you replacing the drier vent that is currently in the wall? You are not planning on reusing the old vent, which is probably plugged up with lint are you? If you are replacing the vent stack, are you removing the drywall or just pulling the new vent up the cavity?

If you compress a 4" round duct into an oval, you reduce the volume of the duct, that is probably not a good idea. The best thing would be to remove the drywall, replace the duct with a new rectangular duct with the same cross sectional area as a 4" round duct (about 12.5 sq in) and then put up new drywall or mud in the old if you cut it right.

You could try cutting the drywall right in the center of the studs so you could put the old piece right back, then tape and mud the seams. Another trick is to cut the drywall on either side of the duct at a 45 degree inward angle. Be careful if you use a drywall saw in case there are wires or pipes in the cavity. This way the cut out piece will fit right back in place, the V shape of the cut will be self supporting.

Re: 4 Inch Dryer Duct in 2x4 Wall

Yes I am considering replacing the old 3"x4" rectangular duct in the wall. It is clear and free flowing with no lint build up. I have removed the drywall on the backside of wall. The laundry room backs up to my garage, so I removed the drywall in the garage side where the vent was, exposing the entire run up the wall and out thru my roof. On the garage side the drywall goes higher up to the rafters where as in the laundry room there is a ceiling with an attic area above. Thus by removing the drywall on the garage side I can see into the attic area.
I did not know the vent was there. When I cut an inspection hole I found the duct. The previous owner had disconnected the vent duct and punched thru directly into the garage. I am sick of it venting into the garage, let alone the code violations and hazards this creates and want to change it.
So my concern again is the physical contact of a slightly ovalized duct with the drywall and the heat that it will be exposed too. I have touched the flex line and it gets very hot to the touch. I can put my hand on it but it is not comfortable and eventually end up pulling it away.

Re: 4 Inch Dryer Duct in 2x4 Wall

If the 3x4 duct is clear and free flowing, no lint buildup, I would leave it there and reuse it. The round dryer ducts have a spiral ridge in them that makes them flexible and that will catch lint and plug up. I would not recommend it. If you are think of using a rigid round duct, pressed into an oval shape, that would be less problematic, but it won't have the cross sectional area of the 3x4 square so it won't pass as much air.

As for the heat, that won't be a problem unless you get a lot of lint trapped in the duct and it catches fire. I don't know if that really happens but a scare ad is run on TV about that, but they are trying to sell a duct and dryer cleaning adapter for your vacuum cleaner. The dryer vent does get hot to the touch, but nowhere near the ignition temperature for drywall. If it got that hot, your clothes would not survive the drying cycle.

Re: 4 Inch Dryer Duct in 2x4 Wall

You have the ability to move your laundry area to the garage? Venting seems like an issue here and venting in the garage sounds like a architect mishap. I would build a new room and then vent the new room directly thru the wall to the outdoors. THanks

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