The Stack Effect
Condensation typically comes from open crawl spaces, and possibly the biggest frustration open crawl spaces cause is the stack effect. This describes the effect that occurs when there’s an entrance for air in the crawl space and in the attic; air enters in the crawl space, warms up, then rises through the home until it exits through the crawl space.
Although this might not be a concern on its own, it’s definitely a concern when it occurs with open-air vents. When crawl space vents are open, you’re much more likely to have mold, mildew, pests, and other dirty air in the crawl space. Through the stack effect, that dirty air starts to proliferate throughout your home, which can lead to significant increases in respiratory concerns and allergies.
Pests and Insects
No matter how small the holes in your crawl space vents are, there are at least some pests and insects that will be able to make it through. Many crawl space vents have surprisingly large holes, making it very easy for all sorts of pests to come through and make a home in your crawl space, which they often do.
Pests and insects are difficult to get rid of because they can reproduce so fast. If any sort of pest or insect gets into your home and lays eggs or has a litter, you’ll end up with these pests for years and sometimes even longer. When you have open crawl space vents, you’re also going to have pests in your crawl space. The only way to avoid pests and insects in your crawl space is to close off your crawl space entirely.
High Energy Bills
One of the biggest problems you might encounter if you don’t have a closed crawl space is high energy bills. It’s extremely common for people to have very high energy bills with any open crawl space for two reasons: the introduction of moisture into the crawl space and the fact that crawl space vents leak warm or cool air out into the world, rather than keeping the warm or cool air in the home where it belongs.
The first point comes from the fact that high-moisture air is much more difficult to condition than low-moisture air. That means you often have to turn your air conditioning up, which increases your energy bills. The second point comes from the fact that crawl space vents don’t discriminate between air that’s coming in and air that’s going out, so your home’s air can go out as easily as outside air can come in.