When Should Crawl Space Vents Be Open And Closed?

As a homeowner, you have to make many decisions to keep your home in a good working condition and avoid any damage to your property. Keeping your home’s crawl space vents or foundation vents open or closed is one such issue. Many homeowners wonder why these vents are installed in the first place and whether leaving them open or keeping them closed will affect the home’s ventilation efficiency.

While ventilation is an important issue for any home, crawl space ventilation needs extra attention. Your crawl space vents play an important role in keeping your home’s foundations moisture-free, so it’s critical to know when to open or close your vent.

Use foundation or crawl space vents to ensure proper airflow and temperature regulation in your crawl space. Crawl space vents are typically opened during the warmer months when you want to keep outside air circulating under the floor and help prevent mold growth. On the other hand, they should be closed during the colder months to keep warmth in and cold air out to prevent the pipes in the crawl space from freezing.

What are crawl space vents?

Often found in older homes, crawl space vents are small openings that allow air to escape from your basement and help prevent moisture from developing. Usually, these vents are often covered with wire nettings, metal grids, or slats. These coverings allow air movement while also stopping rodents and other small pests from getting in.

Are crawl space vents necessary?

The main purpose of foundation vents is to maintain a certain amount of airflow. In certain parts of North America, building code stresses that these vents must be present, but you’ll find that most are required in areas prone to humid summer weather.

Recent research by building scientists suggests that closed and unvented crawl spaces remain significantly drier and mold-free than open and vented ones, irrespective of the weather. 

When should you open and close the crawl space vents?

Crawl space vents can serve as an important function to help cool your home in the summer, but they can also lead to energy loss during the winter when cold air is constantly moving in through these vents.

Building experts suggest that the crawl space vents be opened and closed according to the weather. Crawl space vents can remain open during summer (if your building code strictly demands) but should be closed during winter to limit the moisture buildup. The cold air entering the house foundations through these vents can freeze the pipes in the crawl space. It is especially important for areas where the temperature drops below the freezing point.

If your building laws aren’t strict about keeping the crawl vents open, it’s better to close these vents permanently. New research has shown that crawl space vents are responsible for many moisture-related problems in these houses, and sealing off these vents can prevent these problems in areas where the humidity level is high.

Benefits of closing crawl space vents

You’ve probably heard that it’s important to keep your crawl space vents open to promote airflow and allow moisture to escape, but there are several reasons why you might want to leave them closed. 

  • Closing down these vents will lower your heating and cooling bills by preventing cold air from seeping in and warm air from escaping. 
  • Humidity encourages mold growth. Keeping your vents closed will discourage condensation and moisture buildup that results in mold, mildew, and corrosion. 
  • With your crawl space vents closed, pests won’t be able to enter to chew their way through wiring or any other parts, saving you time and money.
  • Too much moisture in a crawl space leads to structural problems like rotting floors, beams, walls, and cabinets. So, you can reduce the chances of structural problems by closing crawl space vents.
  • The stack effect can transport mold spores and harmful dust into your home. Keeping crawl space vents closed improves your home’s air quality by preventing moisture buildup that leads to mold.

How to close crawl space vents in the winter

If you decide to close the foundation vents, special foam blocks or crawl space vent covers are available to seal the vent from outside when the weather changes to cold. Another good option is to install automatic vents that operate without electricity. These vents close automatically when the temperature drops to 40 degrees and open up when it is 70 degrees.

When the cold and freezing season ends, remove these covers. When taking the plugs off, pay attention to the vent screens. Make sure that the screens are not damaged. Make repairs as necessary to prevent pest infestation. 

Additional tips to keep the water out of crawl spaces

As an extra precaution to keep water and moisture away from your crawl space, take the following measures outside your crawl space:

  • Form a proper drainage mechanism around the home
  • Install efficient gutters and water spouts
  • Building eave overhangs with plenty of clearance

However, in addition to the precautions that you take outside the house, ensure to take some measures inside the crawl space. It includes crawl space encapsulation that involves adding a duct system from the home’s HVAC system to dry off the moisture in the completely closed crawl space. However, you can also opt for a stand-alone dehumidifier after properly sealing the crawl space.

Final thought

In the past, builders and contractors used to think that the crawl space vent allowed cool air to enter your crawl space and help keep it dry as a result, leaving the vent open seems like a good idea at first. However, with more research into this matter, the building scientists now recommend sealing off the foundation vents is a better choice. Especially in an area where temperatures often fluctuate, closing your vents can help prevent moisture and condensation issues with your foundation. 

While closing crawl vents in winter and opening it again in summer works for humid places with harsh winter, encapsulation is your best option for dry weather.

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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