When Should I Open or Close My Foundation Vents?

Many homes have foundation vents, which are metal vents on the home’s exterior right over the dirt line. You can adjust them, opening or closing them as needed. When should you open foundation vents and when should you keep them closed?

Close your foundation vents in the summer to prevent humidity from getting into the house. In the winter, open the foundation vents to improve air circulation and remove humid air from the interior.

In today’s article, we’ll explain further what your foundation vents are and help you create a timeline for opening and closing them. Make sure you keep reading, as there’s lots of great information to come!

What Are Foundation Vents and Where Do I Find Them?

Let’s begin by discussing foundation vents, how they work, and where to find them.

Foundation Vents 101

Foundation vents go by another name, crawlspace vents. Many homes have foundation vents, which act as a form of air circulation for your property.

Built from metal for durability, foundation vents are traditionally rectangular. As the name implies, you’ll find these vents mounted to the exterior of your home rather than the interior.

Foundation vents may begin closed, but at any point, you can open them. This releases warm interior air outside and introduces passive airflow.

In tight areas like a crawlspace where natural airflow doesn’t otherwise exist, foundation vents keep the air fresher and cleaner.

Where to Find Foundation Vents

Go outside your home. If you have a crawlspace, search around the crawlspace. There, a few inches over the dirt line, you should see a foundation vent or several.

Even if your home doesn’t have a crawlspace, it may still have foundation vents. You’ll find them mounted outside. Keep your eyes on the dirt line, and you’ll trace yours down in a couple of minutes.

How Do Foundation Vents Work, Anyway?

You probably know the common principle that heat rises. That goes for the air in your home just as it does anything else.

As the warm air in your home rises toward the top floors, foundation vents will begin pulling exterior air. This outside air combats the moisture inside the home, preventing the interior from becoming overly humid.  

When to Open Foundation Vents

You’ve found your home’s foundation vents. If you’ve never touched them before, expect the vents to be closed. 

You feel like you should open them, or should you? When do you open foundation vents?

That depends on where you live and what kinds of temperatures you get in your region.

For example, let’s say you live in a region where winter temperatures often get well below freezing. You’ll want to open the foundation vents in the summer.

In the winter, the harsh temperatures mean leaving the vents open would fill your home with frosty air. Your heater would have to work practically nonstop to keep your home even moderately comfortable, and you’d almost always feel like there’s a chill in the air.

By the time summer comes, you gladly take the reprieve from the cold. If you experience milder summers, opening your foundation vents will allow fresh air to flow through the house without the risk of making the indoor environment too humid.

What if you live in a region where you get very hot and humid summers? Then you want to open your foundation vents in the winter instead.

This might seem like a strange time to open your vents. After all, what about the issue we just talked about where all the cold air would push into the house, making your heater less effective?

Well, if you have milder winters, keeping your foundation vents open in the winter truly is the best choice.

The damp air that accumulated during the soggy summer season can freely exit. The mild winter air that enters the home feels fresh because it’s drier. That air will refresh your home by improving the rate of air circulation.

When to Keep Foundation Vents Closed

Now let’s look at when you should close your foundation vents.

Once again, there’s no one right answer, as it’s dependent on the season and your region.

If you experience very cold winters, you shouldn’t open your vents until the summer. You will inundate your home with freezing cold air, as we discussed in the last section.

If your region gets very hot summers but not-so-bad winters, close the vents tight when summertime comes around.

Should you not do this, you’re inviting humidity into your home.

Some homeowners don’t stress too much about this, but they should! If you’ve never experienced high humidity in a home before, it does far more than cause condensation on your windows like what you see on your bathroom mirror after a shower.

High humidity can lead to all sorts of issues, so let’s go over them now.

  • Peels wallpaper: The wallpaper throughout your home sticks via glue. Excessive moisture can cause the adhesive to come loose, leading to your wallpaper falling off the wall!
  • Respiratory issues: It’s not just your imagination – it’s indeed a lot harder to breathe in a home with too much humidity. You’ll huff and puff and find yourself out of breath, which can make everything from exercising indoors to simply relaxing with your family an unpleasant experience.
  • Skin issues: While too much dry air will dry out your skin, high humidity will ramp up your skin’s sebum production. This might mean an uptick in whiteheads, blackheads, and acne.
  • Hair issues: Frizzy hair, who’s there? You! If your hair poofs out like a Chia pet in the humidity, you’ll be in for a lot of bad hair days.
  • Worsening allergies or asthma: If you have a preexisting respiratory condition like asthma or allergies, you could aggravate these conditions with all the humidity in your home. Closing the foundation vents and opening them again in the winter will help.
  • Window damage: The condensation that forms on your windows and the damage that humidity can wreak on wood puts your windows at risk of failing on you prematurely. You’ll need some substantial room in the budget for a window replacement.
  • Mold or mildew growth: The fungi mold and mildew love damp, warm environments such as your home. You might see mold in more than the bathroom or basement but in the living room, bedrooms, and possibly the kitchens.
  • Electronics damage: Moisture and electronics do not mix. If the humidity levels rise enough, you could risk breaking your television, smart devices, video game consoles, and other electronics.
  • Wood rot: We saved what is by far the most severe consequence of humidity in the home for last, and that’s wood rot. Overly moist wood can become swollen and soft, putting the very foundation of your home at risk.  

Can You Leave Foundation Vents Open All Year? What About Closed?

In only some regions can you consider keeping your foundation vents open all year long. For this option to be feasible, you’d have to experience very mild temperatures in both the summer and winter.

Even then, if it gets a bit chilly, know that open foundation vents look mighty enticing to a cold critter. You’ll have to add reinforcement screens or creatures such as rats and raccoons could end up in your house!

As for closing your foundation vents all year, there’s never a time when that’s feasible. You don’t want to breathe in stale, possibly humid air all year long, do you? Open your vents from time to time per the instructions from earlier.

How Much Does It Cost to Install Foundation Vents?

Your home doesn’t have foundation vents, and you’re interested in adding some. How much will you pay to do so?

The vents don’t cost much at all. The lowest you’ll pay per vent is $15. More expensive vents cost up to $150 each. 

You can purchase the vents and install them yourself or just buy them and hire a team of professionals to install them.

You’ll likely spend a few hundred dollars on the project to around $1,500 or more with professional installation. That’s quite low-cost!

Should You Get Foundation Vents If You Don’t Have Them?

Before you take the plunge and get foundation vents installed around your home, we want to address whether this addition is worthwhile today.

For a long time, the consensus was that crawlspace vents were the only efficient way to keep moisture from accumulating in your home. Over the past 10 years or so, that line of thinking has become unpopular.

The U.S. Department of Energy suggests that homeowners considering foundation vents should seal up their crawlspaces instead, as that will go a long way toward preventing moisture accumulation than opening or closing some vents.

Crawlspace sealing costs considerably more money, between $1,500 and $15,000. Most homeowners will pay $5,500 on average.

It’s not always necessarily warranted to forego foundation vents. For example, if you live in an arid region, a marine climate, or in an area near 100-year floodplains, you should use foundation vents rather than crawlspace sealing.

As for those living in every other region? Which solution you choose depends on how much moisture you deal with in your home.

If you barely have a problem with humidity, you can probably afford to leave your crawlspace unsealed and get some foundation vents installed. You’ll control humidity throughout the year by opening and closing them strategically.

However, in moister regions, we’d suggest sealing your crawlspace. Even if you can’t afford the work right now, budget for a while, save up, and then get back to the project. Don’t sink money into foundation vents, as they might not help you as much as you were hoping.

Final Thoughts

Foundation vents, also known as crawlspace vents, can filter out humid air and introduce fresher air, depending on whether you open or close them. These exterior vents are better off left open some times of the year and closed during other times, but those periods vary based on the region you live in.

Hold off if your home doesn’t have foundation vents and you’re contemplating adding them. Although it’s more expensive, for many homes, the best way to combat humidity in the house is by closing off the crawlspace.

That doesn’t apply if you live in a very wet or dry region, but it does most everywhere else. Of course, if you barely have a humidity issue, you’re free to continue using foundation vents. They should help!

Considering all the damage that excess humidity can wreak, take your time mulling over this big decision.


Geoff Southworth is the creator of RealEstateInfoGuide.com, the site that helps new homeowners, investors, and homeowners-to-be successfully navigate the complex world of property ownership. Geoff is a real estate investor of 8 years has had experience as a manager of a debt-free, private real estate equity fund, as well as a Registered Nurse in Emergency Trauma and Cardiac Cath Lab Care. As a result, he has developed a unique “people first, business second” approach to real estate.

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