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How to Vent a Home Crawl Space

Kenneth Crawford

To help control moisture and prevent mold under your home, it is a good idea to install crawl space vents. Many older have vents, however, most newer homes do not. Crawl space vents help your house to breathe and remove the moisture that becomes trapped under the house. You can install new vents or replace older vents yourself and save money. Take a look at your foundation to see what you type of material make up your foundation walls.

Concrete or Block Installation

Step 1

Purchase the correct number of crawl space vents for your home. A good rule of thumb is to install one square foot of vent for every 150 square feet of floor space. Most big box hardware stores carry the metal crawl space vents with the adjustable vents.

Step 2

Set the crawl space vent over the outside wall of the crawl space. Lay a four-foot level across the top of the vent and level the vent against the wall. Trace the outline of the vent onto the wall with a pencil.

Step 3

Drill holes around the inside edge of the tracing with a ¼-inch drill bit if you are mounting the vent to concrete or block.Tap a cold chisel with a hammer around the drill hole perforations to break the block away from the foundation.

Step 4

Set the aluminum crawl space vent into the opening. Smooth out the opening with the cold chisel as necessary for a snug fit.

Step 5

Insert the barbed end of the supplied tabs into the back of the vent. The tabs will slide into the vent. There is a hole on each end of the vent for a set screw. Place the supplied nut on the outside of the hole and thread the set screw to the nut from the inside of the vent.

Step 6

Position the vent inside the cut-out hole in the crawl space. Tighten the two side set screws with a flathead screwdriver to hold the vent in place.

Step 7

Read the instructions on the premix concrete bag. Add the appropriate amount of mix and water in the five-gallon bucket and mix well. Apply the concrete to the outside perimeter of the crawl space vent and the concrete wall with a trowel. Do not place concrete on the fins of the vent.


Step 1

Place the inside of the flanged crawl space vent over the crawl space wall. Place a four-level across the top of the vent to level the vent against the wall. Trace the inside rim of the vent onto the wall with a pencil.

Step 2

Drill a ½-inch hole on the inside of your tracing at all four corners with the drill and a ½-inch hole saw. Cut the hole out for the crawl space vent with a reciprocating saw.

Step 3

Set the crawl space vent into the hole with the back side going in first. Press the flanged front flush against the foundation wall. Secure the vent to the wall with the retaining wood screw supplied with the vent.

Step 4

Apply a bead of silicone caulk around the perimeter of the vent with a caulking gun.