Several homeowners seal off large vents all year round in order to avoid termites in the summer, heat loss in the winter, and moisture build-up that can lead to mold growth; others open up and close the vents with the seasons. Is there a single right answer here? This is a topic that the majority of homeowners frequently tackle, as most homes are constructed with crawl spaces rather than basements. Homeowners most frequently seal their vents due to excess moisture in the crawl space, which can lead to a multitude of costly problems (including bowing floor joists, mold, and insect infestation). There are a variety of important factors in this regard and the remediation of the issue, which entails further measures apart from the closure of your vents. Many experts have different views, but we consulted with Elite Moisture Solutions about what they recommend since they mostly deal with issues that can arise from too much moisture accumulating that can result in mold growth.

NOTE: Below are the historic recommendations of when to open and close your crawl space vents, but following these recommendations can lead to issues that can be quite costly, so make sure you read everything in the article before settling on the historic recommendations.

Close crawl space vents during winter

During winter months, keeping the open vents decreases the energy efficiency of your home by allowing cold air to leak in from the outside. Furthermore, if temperatures usually drop below zero, the pipes in the crawl space are more likely to freeze if the vents are open, so it’s usually recommended to close the vents during winter.

Open crawl space vents during summer

Historically it’s been recommended that during the summer keeping the vents open it will allow the moisture to evaporate, but there are downsides to this method. By keeping the vents open, warm moist air will enter your crawl space from outside contributing to condensation and accumulating water. The floor joists and vents are porous and easily wick water vapor from the air; the crawl space can rapidly absorb moisture. This also makes your crawl space an appealing breeding place for vermin, including termites and other wood-degrading insects. If you keep the interior of your home cool in the summer, this can influence the rate of water pooling in the crawl space due to condensation.

Should I keep my crawl space vents open or closed?

Properly closing off the crawl space and eliminating humidity from the ground air is part of a solution aiming to provide a moisture-free and insect-free atmosphere that contributes to a more energy-efficient and safer home.

A crawl space should be completely enclosed and separated from the ground and the humid outside air to prevent it from any moisture. An efficient way to minimize moisture and humidity is to install a crawl space encapsulation system.

The Seasonal Approach

If you don’t plan to seal off your crawl space vents permanently, the easiest way to close your winter crawlspace vents is to plug them from outside with specially made foam blocks for crawlspaces. Remember to remove the plugs as the weather turns milder in the spring, and when you do, make sure your crawlspace vent screens are intact so that insects and rodents don’t make nests underneath your house. You may also opt to go with automatic vents designed to operate without electricity, opening at about 70 degrees and closing at about 40 degrees.