Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/892198
HOUSE CALLS — October 2017 30 Is it ever OK to install a transfer grille? Sure. In the house where I took the photo above, there's no access to the crawl space from outside, and the owner doesn't store hazardous chemicals down there (unless you consider wine hazardous). The bottom line The best way to deal with the air in a crawl space is to encapsulate it and install a dehumidifier. Adding supply air from the HVAC system is tricky and may let the crawl space humidity go too high in spring and fall. Now, go out there and turn those netherworlds into better worlds! House Calls is a new feature column in Healthy In- doors Magazine, which focuses on building science, energy efficiency, and building performance issues. Allison Bailes, III, Ph.D., Energy Vanguard, LLC, Decatur, GA. Dr. Bailes has a PhD in physics from the University of Florida. After starting off on the traditional ac- ademic path of teaching, he found a way to use his interest in energy and the environment, as well as his love for build- ings, especially homes. After finishing the construction of his own green home in 2003, he became a home energy rater, and later founded Energy Vanguard in 2008. Energy Vanguard is more about teaching and less about fixing, although they do offer HVAC design services. It's fo- cused more on the big picture—creating markets, spread- ing the word (such as for Energy Efficient Mortgages), expanding networks—and less on individual components. The company is on the forefront of change—the van- guard—in the way we see and use energy in our homes. For more information, visit https://energyvanguard.com. you can buy for $200 to $300 may be sufficient. For me- dium to large crawl spaces, however, it's best to go with a more robust model, like the ones made by Therma-Stor. Their Santa Fe line is made for basements and crawl spac- es. The photo above shows an older Santa Fe model made just for encapsulated crawl spaces. Conclusion: Although more expensive, installing a dehu- midifier is the best method for treating the air in an encap- sulated crawl space. Should you connect the crawl space to the house with a transfer grille? Both of the quotes from the building code that I mentioned above include the following language: ...including a return air pathway to the common area (such as a duct or transfer grille) What they're saying is that if you pressurize the crawl space with supply air or depressurize it with an exhaust fan, they want the crawl space to be able to communicate with the house above to relieve the pressure. The easiest way to accomplish this is with a transfer grille right in the floor, as you see below. Advanced Energy isn't a fan of this method, instead rec- ommending that the entire floor be air sealed to isolate the crawl space from the house. There are some good rea- sons for this. If, for example, the intent of the opening is for house air to move downward (as in the case of the exhaust fan), the stack effect may win out if the crawl space isn't perfectly sealed to the outside. Another potential problem is pollutants in the crawl space air migrating into the house. These could be soil gases such as radon or fumes from paints, pesticides, or fuel stored in the crawl space. Also, if the crawl space ac- cess door is left open, it may not be discovered for some time. Meanwhile, the house is directly connected to the outside through that transfer grille. i