My first-floor half bath vents into the crawlspace, which violates the code, and I would like to correct it. A feasible way is to extend the hose from the current vent in the crawlspace to the nearest wall, and to cut an opening there. However, the wall in the crawlspace is concrete with rim joist sitting on it, and both are difficult to cut, and may affect the strength of the structure. I want to use the existing vent opening in the wall, is it feasible? Is it easy to remove the vent? Is there any adapter as the opening is a rectangle?

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1 Answer 1


That looks like a vent for the crawl space that is rendered useless because of insulation behind it.

You can use it after cutting away the insulation directly behind the vent.

Then cut the vent at one end to install something like this 4" vent cap.

Install the vent cap and attach the vent conduit in the crawl space.

Cut a cover out of a piece of wood or the removed insulation to cover the remaining crawl space vent opening. (It is only needed temporarily in the event of very cold temperatures, and can be placed from the outside.)

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