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House Vents Open or Closed?

Is it better to close or open the crawl space vents in your house? The answer might not be that simple. This article covers the need for opening or closing vents, and how to do it.

Close up of wooden house with vent, blue sky

For new homeowners, there are many aspects of a house that are uncharted territory. Venting, for instance, is often something people don’t know much about despite how important it is. To be honest, an uneducated choice has the potential to make or break your house.

As a general rule, crawl-space vents should be open in the summer to prevent moisture from building up but closed in the winter to keep pipes from freezing.

Paint peeling off wall, frozen silver pipes

Sounds simple, right? Well, it can actually be problematic. Because of the effects of your vents being either open or closed, there is more to this question than just a quick yes or no. How, why, and when are also important aspects of venting that you should know the answers to so that you know as much as you can about whether to close or open crawl space vents.

Should Your Crawl Space Vents Be Open Or Closed In Summer?

Open! Open, open, open!

It is very important that your house vents are open during the summer but it can be for different reasons.

Summer flower field, sunset, blue sky

When your vents are closed in the summer, moisture builds up inside and can damage the foundation of your house. This is especially prevalent in areas with high humidity and summer storms. Moisture within your crawlspace can lead to mold and mildew, so it is important to allow airflow through your home.

Gasses and fumes can get trapped inside your house if you aren’t careful, but opening your vents allows them to escape hopefully without causing any harm. Because you can’t smell every fume like you can smell a gas leak, you should still be sure you have detectors in almost every room.

Carbon monoxide detector installation

Other negative effects might be moisture collecting on wires or cables that run through your crawl space, damaging them and causing much more trouble than you deserve. It can be a big expense to replace that wiring, not to mention the potential power loss you’ll have to suffer through until it gets fixed.

Should Your Crawl Space Vents Be Open Or Closed In Winter?

As seasons change, so too does the weather.

Blanket of snow over hills, snow-covered trees, dark stormy sky

Much like the need to cover broken windows with insulating plastic to keep the warm air inside, crawl space venting should be closed to keep the cold air out. This is largely to prevent pipes from freezing during the winter.

This isn’t vital or necessary, not technically, but it might save you a lot of trouble in the future, particularly if you live in an area with temperatures known to drop to or below freezing.

How Do You Close Crawl Space Vents?

Closing house vents is, unfortunately, a bit more complicated than opening them. To spare all of us from long paragraphs of tedious instruction, I’ve broken things down step by step.

Here are the seven steps of closing crawl space vents:

  1. As Always, Safety First!

You will want to make sure that none of your furnaces or heaters in the crawl space are just filling the sealed area with fumes or gasses. Be sure to check your crawl space thoroughly with detectors until you are satisfied that nothing is leaking.

The previously mentioned furnaces and heaters? Yeah, they need to have their own direct venting to the outside if you’re planning on closing those vents for the winter. Otherwise, even if you don’t find anything beforehand, chances are that small space will fill up with a dangerous amount of output from either source.

Images of carbon monoxide sources
  1. Seal & Fill

Now, it’s time to seal or fill any cracks and holes you find in flooring, roofing, or foundation.

I know this can be a hassle, but doesn’t it kind of defeat the purpose of closing vents if cold air can still seep in through little cracks and holes?

The best way to fill cracks in concrete, such as a foundation, is with urethane calk or PolyRenewal from Foundation Recovery Systems.

The best way to fill cracks in wood is with wood putty or wood filler sticks. These can typically be bought at any home repair store.

Close up of white brick wall crack with yellow crack filler
  1. Humidity

It may be winter when you’re closing your vents, but humidity can still be a problem! Any kind of moisture in your crawl space will increase the chances of pipes or wires freezing. The best way to avoid this is to place some sort of dehumidifier in your crawl space that will work to keep the air dry, and your pipes and wires safe!

Concrete basement with water damage, big yellow heater drying it out
  1. Flooding

Unfortunately, depending on your location flooding is a genuine possibility. This doesn’t matter whether the vents are open or shut, but you should definitely take measures to prevent it from happening to you.

According to Foundation Recovery Systems, flooding can be caused by any one of three reasons: through open vents or doors, leaking through cracks or holes in your foundation, or heavy downpour that saturates the soil around your home.

To prevent this, you can seal vents and cracks, or install a moisture barrier to guide any water out of your crawl space.

Basement with water on the concrete floor
  1. Inspection Gap

Termite or other insects can get into your crawl space and either eat away at your home or cause other problems. This is why it’s necessary to leave an inspection gap, or an easy access to the crawl space for pest control to do their job!

Damaged wood with termites

If you’re more of a visual learner, here is a quick informational video from Crawl Space Ninja.

  1. Close It Off

At last, the time has come to complete the job! There are different ways you can seal your crawl space but the best way, hands down, is to go with the foam board or block. These will fit in your crawl space vents and provide a snug seal from the outside.

White styrofoam blocks

Foam vent blocks can be found on websites such as, where you can search for the one to best fit your vent size.

  1. Hire Someone Instead?

Now that I have laid out the steps, it’s time to decide whether you would prefer to save yourself the trouble by hiring a contractor instead. If not, I suspect you’ll be getting to work very soon!

If so, let me give you a piece of advice. Get multiple estimates from different contractors before deciding who to go with. It’s important to know your options before jumping in, and this is the best way to do it.

Good luck!

Exposed basement cinderblock walls, exposed pipes and wires, rocks on ground

How Do You Open Crawl Space Vents?

Fortunately, opening vents for the summer is a lot easier than closing them for the winter. The main thing is to reverse step 6, taking your foam vent blocks or other sealants out. Your dehumidifier can stay in your crawl space all year round if you prefer, to protect your foundation and flooring from mold and mildew, and so can any preventative measures for flooding.

Flooding is a bigger possibility in warmer seasons thanks to melting snow and storms, and open venting.

You can also revisit step 7, and simply hire someone to take care of the work for you! I know this would save me from a lot of stress – what about you?

Crawl space opening, ladder

I’m sure none of us had any idea what to do about house vents before this article! For more information about crawl spaces, other than just venting, be sure to check out!