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Another dryer vent question

Ira Broussard | Posted in General Questions on

New construction, zone 2, 10 miles from Gulf Coast. Trying to decide how to vent the gas dryer. The house has a three feet tall (to bottom of floor joists) unvented crawl space on top of a concrete slab, with CMU block walls for the perimeter stem walls enclosing the entire unvented crawl space. As the picture shows, the front porch also has  crawl space, but it is vented. There is a block wall between the unvented and vented crawl space, with an access “door” to get from the unvented space to the vented porch crawl space.

One easy way to vent the dryer would be to drop down thru the floor into the crawl space, then go parallel with the floor joists and thru the block wall between the house crawl space and porch crawl space, then terminate it the porch crawl space. I know one downside of doing this is that to clean the duct well, someone has to go into the porch crawl space. Any other reasons not to terminate the duct in the porch crawl space? Will it cause a detrimental moisture build up in the vented porch crawl space? All of the framing lumber for the porch is treated. Porch floor will be a composite.

I could also have the duct make a left turn before it gets to the porch crawl space wall, then terminate it outside the crawl space, but that would “expose” the vent cap, etc. This would also require the duct to go thru the CMU block wall and the exterior brick veneer.


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  1. qofmiwok | | #1

    This isn't a direct answer, but in PassiveHouses when someone wants a vented dryer it is often recommended that they use a powered damper for airtightness. The danger of that approach is that lint can build up on the damper. So if you do that you are told to make the damper box accessible, either right in the laundry room, or in the crawl if you are willing to be diligent about going down there to clean it regularly. Then you run the exhaust from there to the outside.
    So how this applies to your situation is, maybe you could have a solution which captures a fair amount of the lint inside, and not have to access the difficult location very often.

  2. Expert Member
    Malcolm Taylor | | #2


    Worth checking you code before making a decision. Here anyway it wouldn't fly to terminate in the porch crawlspace, vented or not.

  3. Expert Member
    Zephyr7 | | #3

    I would not terminate a dryer vent in a crawlspace even if it was allowed by code (which it's almost certainly not). Dryer vents "vent" more than just moist air -- they blow out bits of lint too. That's why rooftop dryer vents usually have a linty patch under them on the shingles of the roof. Dryer vents on the side of a house usually have some fuzzies stuck to them too. If you vent into your crawlspace, you'll fill the crawlspace with lint over time and make a mess, and that's in addition to all of the problems the EXTRA MOISTURE can cause.

    I would run the vent through the block to the outdoors. It's not that big a deal to core through block and brick. You can use a small rotary hammer to drill some pilot holes, then use a power chisel attachment for the same equipment in "hammer only" mode to expand the hole. You can also use a big coring bit, or even contract out the hole drilling to a specialized "coring" company. If you are careful and take your time, you can make a pretty clean hole with the drill and chisel combination. I have done this myself many times.


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