Energy Savings By Sealing Your Crawl Space

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Tuesday, June 11th, 2013
stack effect

There are many hot topics today regarding energy savings for consumers. Most of these topics relate to improving the energy efficiency of homes. Did you know that the natural flow of air in homes is like a chimney; it is called the Stack Effect. So if air rises up through a house and exits out of vents in the roof system, how is the air in the house replaced? The answer is that replacement air is “sucked” in through any size opening in the house below the roof.

Here in the southeast US the climate gets warm and humid during the summer months. Homeowners naturally resort to air conditioning to cool their homes. A common perception of air conditioning is that it dries the air as it cools it. This is true, but the process is not as energy efficient as it could be. Since air conditioning must remove a certain amount of moisture from the air before it can cool that air, we might conclude that the process isn’t as efficient as it would be if the air were drier to begin with.

Now, consider a home with a dirt floor crawlspace and open foundation vents. Next consider that up to 50% of the air in that crawlspace can be “sucked” up into the living space above. Since the earth emits a constant stream of moisture regardless of whether there is any water intrusion, and open foundation vents actually function as air intake openings, what do you suppose the humidity levels might be during the summer in dirt floor, vented crawlspaces?

Some folks will tell us that the dirt in their crawlspace is dry, but if they stuck their finger into the dirt a couple of inches, they will likely feel damp earth. Not convinced? The military teaches their survival trainees how to use a plastic tarp, at night, in the desert, to produce condensation for drinking water because the moisture emanating from the desert floor condenses when it hits the cool plastic during the cooler nights.

Back to the energy discussion. Many homeowners are led to believe that those “automatic” vents in foundation vent openings are the “slickest things since sliced bread.” They are controlled by a coil spring which activates at a particular temperature to close in the winter and open in the summer. Sounds good, yes? But do they close enough to insulate and prevent cold air from being “sucked” in during the winter? For you true believers, go into your crawlspace and either put your hand up next to one of these vents, and/or, light a match, blow it out and watch which way the smoke travels. And do we want them to open during those hot, humid summer months when that air will be “sucked” into the crawlspace? Are you getting the picture yet?

If the dirt floor, vented crawlspace could be transformed into an air sealed, dry, insulated part of the total building envelope, would not the air which now is “sucked” up into the living space be drier to cool and heat, and would not the temperature of the air in the crawlspace be warmer during the winter, given that the earth’s temperature averages the annual average local air temperature (55 degrees to 65 degrees in this part of the country)? The answer is a resounding yes.

Now you have an idea how homes with dirt floor, vented crawlspaces are penalized in energy loss. The Department of Energy says that by air sealing such crawlspaces, energy savings up to 30% can be realized. It is also estimated that close to $7 billion of energy is wasted each year from dirt floor, vented crawlspaces.

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