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When To Close The Crawl Space Vents To Your House (5 Reasons To Do It)

Foundation Crawl Space Vent Cover

It’s estimated that over 76 million homes in the US are built with crawlspaces. Chances are, your home has a crawl space. Knowing when to close crawl space vents is something we as homeowners should all be aware of.

Houses are designed with crawl space vents for very specific reasons. Having an understanding of when and why we open and close these vents will help you be a much more aware homeowner.


What Are Crawl Space Vents For?

Crawl space vents are the openings you see, usually in the foundation of your house, which allow the movement and circulation of air into the space underneath your house.

Crawl space vents are generally covered with metal grating, wire mesh or slats. These coverings are meant to allow air to move while keeping pests like rodents and other small animals out.

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When To Close The Crawl Space Vents

You should always close the crawl space vents in your home before winter sets in.  You want to keep out the cold winter air from reaching your pipes.  The other advantage to closing your crawl space vents throughout the winter is it helps keep the wet air out during rainy weather.

The prolonged presence of wet air underneath your house can prevent the crawl space from drying out completely, which can lead to mold and dry rot. A good rule of thumb is to close your crawl space vents once the outside temperature starts dipping down below 40 degrees F.


Tip: Open vents when over 70 deg F. Close vents when under 40 deg F.

When to close crawl space vents open or closed
Close crawl space vents to protect the pipes and wood under your house.


The Importance Of Closing Your Crawl Space Vents

Knowing when to close crawl space vents will help eliminate airflow to the underside of your house and creates an environment with these 5 benefits:

  • Can improve the air quality throughout your house
  • Potential to save in heating and cooling costs
  • Reduce chance of mold and wood decay
  • Reduce warping of wood flooring
  • Creates warmer floors in the winter


What The Pros Say When Asked About When To Close Crawl Space Vents?

According to Tom Silva, from, “…working vents in crawl spaces are a good idea, and so do the building codes, which generally require them. These vents allow outside air to circulate under the floor in summer to prevent the moisture buildup that encourages mildew and rot. In winter, when the air is drier, the vents are closed to reduce the chance that the pipes in the crawl space might freeze.”


How To Close Crawl Space Vents

According to Tom Silva, “The simplest way to close foundation vents for the winter is to plug them from the outside with foam blocks made specifically for this purpose. Just remember to remove the plugs when the weather turns mild in the spring.”  

Silva adds this tip, “As you do that chore, check to make sure that the vent screens are intact so that insects and other critters don’t make a home under your house.”


Different Types of Crawl Space Vents

Automatic Crawl Space Vent Covers

Witten Automatic Vent B-EBLACK(MB)"Energy-Saver" Foundation Auto Vent 8" X 16"- Black
Click to view on

If you’re the kind of person that might not remember when to close your crawl space vents, you’re in luck.  There are automatic crawl space vents available.  The Witten Automatic Vent B-EBLACK(MB) “Energy-Saver” Foundation Auto Vent is very easy to install and like the name implies, it’s completely automatic.  

Once the temperature falls below 40 deg F the vents will begin to automatically close. The vents then re-open once the temperature climbs above 40 deg F.  Another added bonus is that these automatic crawl space vents don’t even require electricity!

Do It Yourself Crawl Space Vent Covers

Construction Metals DVBP 6-1/2x7-3/4 Foam Plug
Click image to view on

But if you’re like me, and like to get out there and close the crawl space vents to your house yourself, then I recommend the foam vent inserts. The foam crawl space vent inserts can be picked up at any local hardware store and are very inexpensive. They simply slide into the vent space nice and tight, and prevent air from passing through.


Inspect For Pests While Closing Your Crawl Space Vents

While you’re walking around the perimeter of your house preparing to close the vents, take that time to inspect the vent screens, or wire mesh.  Like I mentioned earlier, these screens are meant to keep out rodents and other pests.  

If you do see that the screen is torn or holes have been made, take this time to fix it.  And if you happen to see evidence of rodent infestation, take a minute to read my article DIY Rat Repellent: Easy Tips For The Clever Homeowner for a few ideas on how to get rid of those uninvited guests.

Final Thoughts

Hopefully this helps you understand more clearly when to close crawl space vents this year. Once the temperature starts to go back down, take the time to close them up.  Take care of your home and save energy by sealing up your crawl space this next winter.

If you have any additional tips or information regarding closing your crawl space vents, leave a comment. Also, feel free to shoot me an email!  And I’ll list your tips right here.

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