Healthy Indoors Magazine - USA Edition

34 | HOUSE WHISPERER — January 2018 The industry standard test pressure is 50 Pascals, which is the equivalent of a 15-20 mile-per-hour wind against all sides of your house at the same time. With something like that going on, you can find a lot of leaks in a house in a short amount of time. The number on the right (2257) is the leakage reading or what I call the "blower door number." It's measured in cfm50, or cubic feet per minute at 50 Pascals. The unit doesn't matter that much, as long as you always compare the raw blower door reading in cfm50, which is our practice. Every 10 points is roughly equal to a square inch hole. There are 144 square inches in a square foot, so every 1400-1500 on the blower door is equal to a square foot hole in your house that's open 24/7/365. A basketball sized hole is about 0.5 square feet, for reference. The home from this reading is about 1700 square feet. Before any work was done, the blower door number started out at almost 8000. That's over 5 square feet of leakage, ten basketball-sized holes, or one window being open all year. After air sealing work, it was down to 2257. We eventually got it under 1900. That's a little over a one square foot hole or two basketball-sized holes. Let's think of a 2000 square foot home to make the math simple. If that house had a 1:1 leakage:square foot- age ratio, it would have a 2000-blower door number. That's decent; a B or a B- grade. Often a one to one ratio like this is good enough to gain adequate control of the air/heat/ moisture going into and out of the home. For a 1:1 home to work well, however, the top and bottom of those houses needs to be air sealed well. Homes built in the last 20-30 years are usually in this 1:1 range, but often need to be further tightened, because the tops and bottoms are still leaky. (See the 1970s Two Story Colonial or 1996 Center Hall Colonial case studies as examples.) If that same home was built between 1950 and 1970, it might be in the 2:1 range, so it would have a 4000-blow- er door number to 2000 square feet. Delivering comfort in a home this leaky is often attempted with oversized brute force HVAC (Heating, Ventilation and Air Conditioning), and possibly a zoning system. Often the results of brute force HVAC still include 5 to10-degree temperature differences between different parts of the house. Most homeowners re- main unsatisfied, despite having Herculean HVAC systems on the job. Finesse is needed to get comfort, not raw pow- er. (See the HVAC 101 and HVAC 102 chapters chapters for more on this.) If that 2000square foot house was built in 1910, it likely would be in the range of 3:1, or a 6000-blower door num- ber. These vintage homes are drafty and typically very diffi- cult to control. They often experience massive temperature swings, where the basement may be 20 degrees different than the second or third floor. That was the case in the 1915 Case Study Home . Once you know the blower door number, you can begin to make plans. What are the biggest problems to solve? What areas are most likely to affect those problems if they are air sealed? What can be sealed easily? What should be sealed but is more difficult? What is most likely to make the biggest difference to the blower door number? These are the sorts of questions that help you and your Home Performance Specialist begin to design solutions that help address the problems you want to solve. Be sure to set realistic targets for reductions and com- municate them to the crews you work with. Setting multiple targets depending on what upgrades are planned is also important. Nate Adams is the founder of Energy Smart Home Perfor- mance in Cleveland Ohio and of NateTheHouseWhisperer. com. Rather than focus on energy efficiency, Nate focuses on solving the root causes of client problems like uncom- fortable rooms, mold, wet basements, and icicles. As a fan of radical transparency, he has published the most detailed case studies in the industry on these projects. Nate is the author of The Home Comfort Book, a guide showing people how their homes really work and how to truly solve problems, instead of putting band-aids on bullet wounds. It is meant to create consumer demand for this work rather than the traditional supply focus that has been taken for forty years. His writing has been published in numerous outlets in- cluding GreenTech Media, CleanTechnica, the Journal of Light Construction, Green Building Advisor, and more. Learn more at: http://energysmartohio.com/ i

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