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Doing a dryer duct, the right way...

3213 Views 7 Replies 3 Participants Last post by  Gary in WA
I am upgrading the duct on my dryer from a 3" diameter plastic duct to a 4" rigid galvanized steel duct.

Current configuration:
Dryer is located in an unheated basement on an exterior wall.
The plastic 3" duct makes a 90 degree turn "vertical" at the dryer. Runs about 8 ft then another 90 degree turn "horizontal" and attaches to a metal duct/hood with flapper. The duct/hood assembly runs through the rim joist and brick fascia.

Steps I have taken:
I enlarged the hole in the brick fascia and rim joist to 4-1/4". I used a carbide hole saw so it is a very smooth cut.
I bought Heartland 21000 dryer vent closure and painted it to match the exterior brick color.
I bought a few sections of 4" rigid galvanized steel duct, the kind that comes in un-rolled 4ft sections. Also bought two non-adjustable 90 degree galvanized duct pieces. There is not a lot of horizontal duct work, but I will keep the seams facing upward.

Where I need some guidance:

Assembling the duct sections..... Is UL approved metal tape the best product I can use? What about mastic reinforced with fiberglass mesh? I hear clamps can pinch things and screws collect lint. Any product links would be quite helpful.

Attaching the duct sections to cinder block wall.... I guess some type of pipe strap, again a link would be helpful.

The gap between the duct work and the brick fascia + rim joist..... Do I cement the duct into the brick fascia and fill the void in the rim joist with some sort of heat safe insulation?

Designing the duct in a way that it is easily cleanable.... Got nothing on this one.

Designing the duct it so it can be attached and removed from dryer easily.... Should I put a small piece of aluminum flex duct between the dryer and the rigid duct?
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I could use that flexable duct, however, the ridges in this kind of duct create static pressure and would reduce the CFM of the dryer. Ultimately it will cost me more on my electric bill as I will have to dry my clothes longer which is why I would like to use the rigid ductwork. A quick google search on duct roughness factors backs up this argument. 0.0004 rigid galvanized vs 0.007 for flexible metal fully extended.

So 1 vote for sprayfoam on the rim joist/brick fascia. I suppose that makes more sense than cementing it. It would certainly be easier to remove should there be a need to.

and a vote for hose clamps on the connections
The flex duct will be making two 90 degree bends just like the rigid. There is no other way, our rather no better way to run the duct out of my house. There will be two 90 degree bend no matter what duct I install.

So in this scenario the flex duct would inhibit airflow. Not to mention all those ridges inside the ductwill build up lint much faster than the smooth interior of the rigid duct.

hypothetically, if I had the option to make two gradual turns then flex would be better suited. Even then, I still think a rigid duct with an adjustable elbow would be superior.

And your correct, I am being excessive, but I would rather be excessive than lazy.
I bought the heartland 21000 a long time ago and static pressure was the last thing on my mind. Now that you brought it up i can see the air turns 270 degrees before exiting the hood! :( If I go by the static pressure readings on this site those don't bode well for it either.

Opinion on this hood? Looks pretty good? Here is an action video Hopefully it seals tightly.

@joecaption, i stand corrected. The semi rigid aluminum is not as bad as I had thought it to be. I think i will use it for the bottom section as it will make attaching the dryer easy. I will still use rigid duct for the straight sections and probably for the top 90 degree elbow as the space is very restricted there.
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