What is a blower door test?
Blower door tests are becoming a standard part of building codes across North America, and for good reason. In Canada, the BC Energy Step Code is a prime example, and in the US, many states are adopting similar air leakage requirements in their codes, often referencing standards like the International Energy Conservation Code (IECC).
A blower door test is an essential part of most home energy audits, including those required for programs like Canada's Greener Homes Grant program.
The requirement for an air permeability or blower door test is popping up more frequently as codes improve and homeowners demand better, more energy-efficient homes. And why not? Based on standard building practices, it's estimated that air leakage can account for up to a third of a home's total energy loss. That's like leaving a window open all year round.
Controlling this air leakage is critical for saving money on both heating and cooling. In the winter, every time warm, humid air you paid to heat leaks out, cold, dry air is pulled in, forcing your furnace to work overtime.
In the summer, the reverse happens: hot, humid outdoor air infiltrates your house, making your air conditioner work much harder not just to cool the air, but also to remove the extra moisture. Sealing those leaks means significant savings on your utility bills, month after month.
How do you do a blower door test?
This isn't a DIY job you can learn from a YouTube video; you need to hire a trained professional. The process starts by closing all windows and doors. Then, a powerful, calibrated fan is mounted in a flexible panel in an exterior doorway.
The fan sucks the air out of the house, lowering the air pressure inside. This depressurization pulls outside air in through every unsealed crack and penetration in your home's shell, no matter how small.
The operator uses gauges to measure the airflow required to maintain a specific pressure difference (usually 50 Pascals), and from there they calculate your home's air leakage rate, often expressed as ACH (Air Changes per Hour). A typical new home might land around 3 ACH. A high-performance home like one built to the Passive House standard needs to hit a very demanding 0.6 ACH or less.
Even at 3 ACH, which is far better than most older homes, you are paying to heat and cool a huge volume of air that quickly leaks outside. This doesn't just hurt your wallet; it hurts your house.
When warm, humid indoor air leaks into your walls during winter, it can condense on cold surfaces, leading to moisture, rot, and mold. Nothing good ever comes from uncontrolled air leakage. Nothing.
One of our writers had a blower door test done on their own home as part of an energy audit, and the initial result was brutal: a little over 6 air changes per hour. It was practically a wind tunnel.
The energy advisor broke out a smoke pencil to find the culprits, and we watched in horror as the smoke was just sucked clean through the frames of our front door and side door.
It turned out that when auxiliary deadbolts were installed, the hole for the bolt was drilled right through the door stile and the framing, creating a direct, 1-inch-wide highway to the great outdoors.
Worse, it was a perfect spot for interstitial condensation, and sure enough, we found a nasty little patch of mold starting in the wall when we put our fibre optic camera in to take a look. A $4 tube of caulking and ten minutes of work fixed the problem.
On the re-test, we clocked in just under 3 ACH. We cut our air leakage by more than half for less than the price of a coffee, and the improvement in comfort was immediate. This is the "pyramid of diminishing returns for home improvements" in action; that first easy fix gave us a massive improvement. Always find that low-hanging fruit first.
How to find a professional blower door testing company
Okay, so you're sold on the idea - or obligated by code - but where do you find someone qualified to do the test? You can't just look up "dude with a giant fan" in the phone book.
In Canada, your best bet is to look for a local registered energy advisor certified by Natural Resources Canada (NRCan). In the United States, you'll want to search for a certified professional from the Building Performance Institute (BPI) or a RESNET (Residential Energy Services Network) HERS Rater.
These folks are trained and certified as energy auditors to perform proper energy audits, which include blower door testing. They're the real deal.
When you're talking to potential companies, ask what's included. You don't just want a number at the end; you want them to help you find the leaks. Will they walk through the house with you while the fan is running? Do they use tools like smoke pencils or an infrared camera to pinpoint the problem spots?
A good pro will do more than just test; they'll help you make your home better. Don't be shy about asking for a sample report so you know what you're getting for your money.
Getting the right person is half the battle in turning that air leakage number from a scary metric into a useful to-do list for a tighter, more comfortable home.
Finding and fixing air leaks during a blower door test
This is a day when you will want to buy a few rolls of high-quality tape (not the cheap stuff) and invite your friends over for a ‘find the hole and tape it’ party, especially if you're building a new home and the drywall isn't on yet.
With the fan running, you can literally feel the air coming in with your hands or see it with a smoke stick. As we found in our own home, sometimes the biggest leaks can be fixed with the simplest solutions.
As an example, when we built the LEED V4 Platinum Edelweiss House, the rating when we started the blower door test was 1.1 ACH and it dropped to 0.64 ACH after four of us spent an hour sealing up leaks.
The person you hire to perform a blower door test won’t want to stick around all day without charging you handsomely for their company; that is why it’s great to have many people looking for and taping-up leaks. There's even a product that seals up airleaks on existing homes that's pretty cool, see here.
Energy retrofitting tax incentives and rebates
Conducting a blower door test will likely be required for energy-efficient home renovation tax credits and rebates, both in the US and Canada. If you live in a region where these programs are in effect, it's a wise financial decision to take advantage of them.
Many federal, state, provincial, and even municipal governments offer tax breaks and rebates for energy efficiency upgrades. You win on all fronts – you save money on your home renovations, end up with a more comfortable home, and save money on your heating and cooling bills for years to come!
Breaking News: New Canada Greener Homes Grant Scheme 2021 announced - see here for how to apply and eligibility requirements
Now that you know all about the blower door test, visit the Ecohome Green Building guide pages to learn how to install an air barrier, airtight window installation, how to choose a weather resistant barrier (WRB), caulking products and sealants for energy-efficient homes.
Subscribe to our YouTube channel to see our DIY Green Home Building video series and sign up for a free Ecohome Membership here.
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