In terms of energy consumption they show you exactly where the money goes and how to stop the flow. I recently had one done on a new home that I designed that is currently under construction, so lets run through that one so you know how it goes.
The builder, Mike Knutson, and I selected Pat O’Malley of Building Knowledge to perform the blower door test not only because he does a terrific job, but also because he’s so helpful and non-judgemental and I always learn about the latest products and methods. Pat just wants to save the world in his own little way.
In new construction the best time to do a blower door test is after the insulation and vapor retarders are in place but before the drywall is hung. The reason being that at this juncture when you find the problems you can fix them without tearing apart the house. The first thing you do is seal up the house by closing all the windows and doors to make it as air tight as possible, then you open one exterior door and install the blower door.
The unit basically resembles a bright red stretcher with a large fan and an expandable metal frame that can conform to most any door opening. You then use a pressure meter to measure the ambient pressure to determine the baseline and then you crank her up! The idea is to determine how much air you are drawing out of the house through all of its leaks. The 2015 energy code requires homes to have an air tightness level of less than 3.0 air changes per hour at 50 pascals of negative pressure (3 ACH50), and this house measured 1.78 ACH50. Break out the champagne!
Once you’ve determined this number then you get out the infrared gun and the real fun begins. The infrared gun illustrates temperature graphically in a spectrum of colors, red being warmest and blue coldest (since we did the test in the winter the color differentials were incredibly dramatic!). Then you meticulously walk around the entire house checking for areas of blue infiltration or areas of little insulation when there should be a lot. You focus on typical problem areas like basement slab perimeters, base plates at exterior walls where they meet the subfloor, and recessed can lights with attic space above. The gun has a laser pointer so that you can mark all the areas that need to be addressed so the contractor can come back around and fix all of the problems.
The same procedure can be done on an existing house or a remodeling, so do yourself a favor and treat you and your house to a blower door test today!