At one time or another, most homeowners have probably experienced a hot bonus room, a moisture problem, or air leaking in (or out) near doors and windows. These are some of the issues I’m looking for when I go into a home to figure out the best ways to improve its comfort and energy efficiency. There are a lot of things I take into account and some useful gadgets at my disposal. The one tool in my bag of tricks that is both indispensable and raises the most eyebrows from homeowners is the blower door test. Simply put, a blower door measures the total amount of air leaking into or out of any house (or commercial building), and it is often the most important piece of equipment that we use.
Since we get so many questions about it every time we take it out of the bag, we thought we’d offer a quick overview and video demonstration here on our blog for anyone interested.
At first glance, I’ll admit that it is a strange looking set up. I start by opening all interior doors, and making sure all exterior doors and windows are shut. Then I’ll set up shop, usually at the front door: I insert an adjustable frame with a red nylon curtain in the door frame, and then hang a big fan in the middle. That fan is attached to special equipment with a pair of hoses that gauge two very important things: the air pressure outside the house compared to the pressure inside, and the air pressure across the fan.
When I’m ready to start the blower door test, I switch on the fan and it starts blowing air out of the house, which changes the indoor air pressure (This is the point where any neighbors passing by walking the dogs might stop to wonder what the heck is going on!). Next, I adjust the fan speed to get to a specific pressure reading; how hard the fan is working to keep it at that level tells me how leaky the home is. Once we get that reading, the test is over, but the results usually surprise people — a typical home has enough small air leaks that add up to keeping a window open wide all year round. On the other end of the spectrum, in some higher performing homes, a house can be too tight, which can pose a danger because it makes it difficult for fresh air and moisture to get in or out of the home.
SEM's Michael Peaden performing a blower door test.
The blower door is also versatile. When I use it in conjunction with infrared cameras or duct blasters (small versions of blower doors that hook up to duct systems), it gives me even more data and helps me pinpoint problems in a home or building. It really is the one piece of equipment that goes with me to every single home or building performance analysis. The blower door is also a tool that’s used across the entire Building Science community — it is a required part of the testing required for a new home to achieve an Energy Star certification, and it is also used to test the air leakage in large commercial and military buildings.
What it all boils down to is this: while the blower door is certainly an interesting apparatus that people like to watch and talk about when it’s set up in their home, the most important thing about the blower door is the information we get from it. I can visually inspect a house and offer advice based on decades of experience, but without the blower door and understanding the data it provides, there’s no way of quantifying exactly how useful those recommended changes might be.
Bill Klotz is the Home Performance Coordinator at Southern Energy Management. Read more about him here.
Tags: air leakage, blower door, home performance
Its easy and so active
Bill,
I and many other building scientists and high performing home contractors will respectfully disagree with you comment about being too tight. What I’m sure you meant to say was; that in high performing homes,a properly designed ventilation strategy is employed to account for the extremely tight envelope. You perpetuate the myth of “A house has to breath” by suggesting a home can be too tight. This misinformation allows many builders to continue building the same old leaky houses and then slap on some eco-bling and convince themselves that they are building green.
Your credentials are far beyond that underlying message of this post.
Respectfully,
Al Cobb
304-876-8494
Al,
Thanks for taking the time to leave a comment, and your point is well-made. I probably could have said it clearer: a key component of a high performance home is to have a fresh air ventilation strategy. In the context of this post, “too tight” – in building science lingo – would indicate too few air changes in an existing home. In that case, one of our first recommendations would be to address that lack of ventilation. Hopefully that explains it a little better. Thanks again for sharing your perspective.
Bill