This Blows: Measuring air tightness with a blower door test

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After learning about so many neat engineering practices during my undergrad career, I’m finally getting some hands on experience by helping with the construction of a new home. Lately, I’ve been getting my hands dirty, like this past week, when I helped perform a blower door test.

A blower door test is used to measure how tight a building’s envelope is. The standard protocol is to seal a house and connect a giant fan to a fitted opening. The fan depressurizes the house by sucking out the air, thereby creating a pressure difference between the indoor and outdoor environments (usually this is about 50Pa). This pressure difference then causes outside air (which is at a higher pressure) to seep into the house through any openings. The leakage is measured in terms of ACH (air changes per hour), which is the number of times the house’s volume of air can be replaced in sixty minutes (think of a submarine with a leak in it). The more leaks, gaps, and holes in the house’s envelope, the higher the ACH will be.

So why does envelope tightness matter so much? This factor is actually a big component in determining a building’s energy efficiency. Conditioning outside air (e.g. heating cold air up in the wintertime) requires a huge amount of energy. Sealing your building’s envelope is an excellent way to keep outside air from coming in, which will consequently slash your energy bill. With this in mind, my construction team decided to perform a blower door test at our site.

Since the home we’re working on is still in development, the windows and doors had not yet been installed. Our team first had to seal all openings with polyethylene and plywood (lucky for us, it was only 43°C that day). Once finished, we connected the fan and slowly began to draw out the air. First try: we blew the seals on the windows as we ambitiously increased the pressure difference to 50Pa. We fixed the seals that had burst, and were ready for our next attempt. Second try: we tipped 3 ACH at a difference of only 30Pa (our goal was to be around 1.5 ACH at 50Pa). We realized that our envelope must be compromised and began checking for leaks. As a junior engineer, I was thrilled when I found a leak in a perimeter wall. The spray foam had separated from the wall stud, and outside air was seeping through the crack. Sadly, this minor leak was just the beginning of our problems. We later found massive gaps in the basement insulation in some hard to see – and reach – areas. The solution to our problem? Repair the anomalies with another application of insulation and cover other areas of potential leaks with caulking before the dry wall is put up.

Fortunately this house is still in the construction phase, so the issues can be fixed before the walls are complete. Constructing buildings properly from the beginning should ensure tight envelopes and better efficiencies of new developments. This however doesn’t mean that existing buildings are at a total loss. Current owners should look to properly seal their homes by caulking around windows and joints, applying new weather-stripping, properly maintaining fireplaces, dampers, and chimneys, and possibly applying a seal or coating over windows.

These simple measures can help seal openings and prevent outside air from seeping into your home. This approach requires a bit of effort, but will save you energy and money in the years to come. Think of it as a facelift for your home; just a few little tweaks and somehow everything’s tighter than ever!

  • Sandra Dedesko

    Sandra Dedesko is a recent graduate of Civil Engineering at the University of Toronto. She has a high interest in energy efficient buildings and sustainable urban development. She's currently working towards a Masters degree and industry career in this area.

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