Code compliant blower door testing of a small home can be very frustrating for both the person performing the test and the homeowner or contractor who are required to have the test. A few months ago, I tested a 952 square foot, newly constructed home with a volume of 7616 cubic feet, one of the smallest I’ve tested. The house had a leakage rate of 416 cfm which resulted in a 3.28 ACH50 number. A failed blower door test (my climate requires 3 ACH50 or less). If we take that same CFM rate but increase the ceiling height to 9 feet, which changes the volume to 8568 cubic feet, 2.91 ACH50, a passing test. Either way, 416 CFM of air moving through the blower door isn’t much, some kitchen exhaust hoods can move more air than that. Seems unfair to punish smaller homes when blower door testing, especially when the blower door test is testing the surface of a structure, not it’s volume.
I bought my first blower door in 2009, back when new construction was in a downturn and energy auditing and weatherization projects were on the rise. I took a 40-hour energy auditing training course at a local college which included hands-on training on how to use a blower door. It took many tests before I became comfortable in its operation and understood the information it was providing. Though one of the more expensive tools I own, I’ve been able to keep it busy and add this specialized testing to my business’s income stream.
When conducting a blower door test, one of the ways we express the findings is with air changes per hour at 50 Pascals (ACH50). As an example, a new home is blower door tested and found to be 2.75 ACH50, this means the entire volume of air inside the home is exchanging with the outside air 2.75 time per hour at the test pressure of 50 Pascals. When discussing blower door testing with builders and homeowners, it can be hard for them to relate to the ACH50 number other than they know the home needs to be less than a certain level of air tightness to meet current code requirements. Expressing the tightness as natural air leakage can sometimes be helpful. How can we calculate the natural air change rate? Well, there’s a formula:
The main purpose of a blower door test is to confirm the integrity and continuity of the air control layer or air barrier. I have a few different options on how to perform a test. Which option I choose is dependent on the reason I am performing the test.
2012 was the first year the International Energy Conservation Code required residential construction to pass an air leakage rate test, better known as a blower door test. My area of the country requires the test to be at or below 3 air changes per hour at the test pressure of 50 pascals (ACH50). (Other areas, typically warmer climates require 5 ACH50.) Most new construction in my market has no problem passing the test, but I have had a handful of houses fail, usually the failed tests are by a builder having their first blower door test or the project is a very small home.
Whether you are performing blower door testing or hiring someone to perform the test for you, it’s a good idea to understand how a home should be setup for the test. Should a door be open or closed? What can be sealed off? How to address rooms attached to the house but are outside the air control layer? That’s today’s topic, attached garages and three season porches. How should those spaces be setup for a blower door test?
Air leaking into a home (infiltration) or out of a home (exfiltration) happens naturally in every home, new or old. No matter how much air sealing is performed, we just can’t make them completely air tight. I’ve tested some new homes that were very tight, .33 ACH50, (anything under 1 ACH50 is very good) and I’ve also tested many older ones that aren’t so tight, we can use my 1952 Cape as an example, 9.71 ACH50. In this post, I’m going to discuss how to manually calculate the cost of the air leakage and examine what we can do with that number. Continue reading “Energy Audit-Calculating the Cost of a Home’s Air Leaks”
An energy audit is an inspection and analysis of how a building uses energy. To get an accurate analysis, tools are needed to perform testing. You would think that a blower door and thermal imaging camera would be my most commonly used tools during an audit, I do use them often, but there are a couple I used more. This posting is all about my energy auditing toolbox. Continue reading “Energy Audit-Tools of the Trade”
I think most of us know of this man, one of the founders of The Energy Conservatory and designers of the Minneapolis Blower Door. I recently had the opportunity to chat with Gary. My intent with the interview is a little different from other interviews that have featured Mr. Nelson. I wanted to ask questions from a practitioner working in the field point of view. Continue reading “Building Science-An Interview with Gary Nelson”