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If you go this route, it may work well in the summer if the air conditioner is sized properly.
#Clean space vent covers code
The International Residential Code (IRC) recommends 1 cfm per 50 square feet:Ĭonditioned air supply sized to deliver at a rate equal to 1 cubic foot per minute (0.47 L/s) for each 50 square feet (4.7 m 2) of under-floor area, including a return air pathway to the common area (such as a duct or transfer grille), and perimeter walls insulated How much supply air do you need to add to the crawl space? Advanced Energy recommends 1 cubic foot per minute (cfm) for each 30 square feet of crawl space floor area. In Advanced Energy field tests, the small crawl space airflow causes a negligible pressure effect that is far exceeded by the effects of duct leakage, stack pressure or wind-induced pressures in the building. Is that a problem? Not according to Advanced Energy‘s Closed Crawl Spaces guide: The air from the system helps to dry out the crawl space air.īut it also puts the crawl space under a slight positive pressure and the house under a slight negative pressure. If there’s already a duct system down there, it’s easy and inexpensive to do. If you encapsulate the crawl space, adding a little bit of air from the HVAC system is probably the most common method used. It’s probably also worst for most climates if the HVAC systems and ductwork are located in the crawl space. Let’s just say this is your worst option unless you’re in a dry climate and quickly move on to the better choices.Ĭonclusion: This is your worst option in humid climates. The result was mold growing on the HVAC system. Although the home builder had installed closed cell spray foam insulation in all the above-grade walls and the attic, he left the crawl space vented to the outside. The photo above is from a house that was only a year or two old. Although the psychrometric chart shows mathematically why it doesn’t work, a look into just about any vented crawl space in the Southeastern US proves that venting to the outside is often a disaster. The outside air that you bring into the crawl actually has more moisture in it than the crawl space air you’re venting to the outside much of the time. Vent the crawl space to the outsideĭo this in a humid climate, and you’re asking for trouble. Let’s take a look at each of these methods.
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The tried and false method of venting the crawl space to the outdoors.So, as always, do what’s most suitable for your climate.īasically, your options are to do one of the following: In a dry climate, it may or not be worth the cost to encapsulate. But what do you do about the air down there?īefore we address that question, however, let me point out that encapsulated crawl spaces are great for humid climates, like the Southeastern US. It’s often seen as the best way to eliminate the moisture problems that often result from vented crawl spaces. Most crawl spaces are vented to the outdoors, but over the past decade, encapsulating the crawl space (as shown below) has gained favor among builders of green and energy efficient homes. The actual dimension of the covers interior frame will be slightly smaller than your rough opening size-this is to ensure that the frame and/or damper fits comfortably INSIDE of the duct opening.If you have a home with a crawl space-or are building or buying one-you have several options on what to do with that particular foundation type. The overall (outside) size of your cover will be larger than the opening size-this accompanies the outside border portion of the cover where the screw holes are placed. Note: This is your opening (inside) measurement. The length and height of your duct opening should match the width and length of specific register/grille you wish to purchase. Step 3: Match the duct opening size to the corresponding vent cover size listed on the product listing. Many of our vent grilles include directional patterns so it is crucial to provide both dimensions in their respective order. Note: The Length (L) is always expressed first, followed by the height (H) dimension. STEP 2: MEASURE THE DUCT OPENING IN YOUR FLOOR, WALL OR CEILING. (LENGTH IN INCHES -BY- HEIGHT IN INCHES) THIS IS YOUR DUCT OPENING SIZE. Step 1: Remove your existing vent cover Note: Do not measure your existing cover.