How To Replace Foundation Vents

Working foundation vents help prevent damage to your house sill plate due to rot or termites.
Working foundation vents help prevent damage to your house sill plate due to rot or termites.

The foundation vents on your home help to prevent moisture under the house by providing air flow.. Excessive moisture leads to rotting wood and termites. Keeping the vents open during the summer allows air to flow under the home, keeping it cooler and drawing out moisture. They also help to ventilate when there are propane or gas lines running under the home. Closing the vents during the winter or even during strong summer storms, helps prevent snow and rain from going directly under the home. Closed foundation vents during the winter also helps to keep the pipes under the home from freezing due to cold winds.

Loose, missing or damaged foundation vents require replacement. The most common foundation vents are installed with mortar. The vents are made of steel and have a screen. There is a handle that allows you to quickly open or close the foundation vents depending upon the weather and the season. Replacing foundation vents requires making sure the foundation vent hole is free from any loose mortar from the previous vent.

Tools and Materials to Replace Foundation Vents

Cold chisel


Stiff wire brush

Quick-drying mortar



Remove The Existing Foundation Vents

Pull loose foundation vents out of the hole, if the vents are so loose that they have no mortar holding them in place.

Chip the mortar away from the perimeter of damaged vents with a cold chisel and hammer. Avoid digging into the foundation wall when chipping through the mortar. The mortar is relatively thin and should chip away with little difficulty.

Pull the center of the foundation vent once you chip away the mortar. If the vent doesn't budge, go into the crawl space and look for mortar adhering the vent from behind. Chip away the mortar and remove the foundation vent from the hole.

Continue chipping away the old mortar from the hole with the chisel and hammer. Brush the inside perimeter of the hole with a stiff wire brush to remove all traces of the old mortar. Pay special attention to the corners of the hole.

Install New Foundation Vents

Mix quick-drying mortar and water into a bucket according to the directions on the mortar bag. The mortar consistency should be like a thin oatmeal.

Apply a thin layer of mortar along the inside perimeter of the foundation vent hole with a trowel. The layer should be less than 1/4-inch thick.

Position the new metal foundation vent into the hole. Apply another layer of mortar along the perimeter of the foundation vent with the trowel. The mortar should overlap the edges of the vent and the inside of the foundation vent hole an inch on each side. The mortar should also be less than a 1/2-inch thick.

Foundation Vent Options

There are also plastic replacement foundation vents available that require no mortar. These secure to the foundation vent holes with a series of screws. The vent hole still requires cleaning just as you would when installing a metal vent. Follow the directions that come with the replacement foundation vent.

Another option is to install automatic foundation vents. These types of vents take the guesswork out of when to open and close the vents. They open and close automatically depending upon the weather and temperature. Again refer to the manufacturers instructions for vent installation and to determine if an electrician is needed for wiring the vents.

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Comments 2 comments

Lee 2 years ago

Where can I find the foundation vents that don't need motar? I do not want the automatic ones. All that I can find are the mortar types.

kenwrites profile image

kenwrites 2 years ago from Yreka, California Author

Lowes or Home depot

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