What’s a blower door test?
“What, were you raised in a barn? I’m not paying to heat the outdoors!” This is what I heard from my mom, when I was a kid and I left a door or window open. Well mom, I’m here to tell you that the heat is still escaping, even after the door has been closed. The leaks aren’t as obvious as an open door or window but rather many small leaks that can actually add up to the equivalent of an open window. So how do you find those leaks? How do you determine if your house is doing a good job of keeping the heat in during the winter, or out in the summer? Your best option is having an energy auditing professional do a blower door test. A blower door uses a fan to exhaust air to the exterior of the house lowering the homes internal pressure. When you do this, air is pulled through every opening in the home which causes the internal pressure to drop. The air leaks are raising the internal pressure and fighting the fan which is working to lower it so a pressure measurement tells us just how much leakage is occurring. The interior of the home is referred to as the envelope of the building and a building with less leaks, indicated by a lower internal pressure is considered to have a “tighter” envelope.
The three main components of a blower door include a powerful fan, a manometer, and the mounting structure that expands to fill and close the doorway. A manometer is just a fancy word for a device that measures pressure. The mounting structure is made of an adjustable aluminum frame covered in an airtight cloth that can be fitted to any door by adjusting the frame.
How do you find the leaks? You might be saying, “okay I understand that the pressure measurement from the blower door tells me how tight my home is but how will it help me find the leaks? Remember, while the fan in operating air is being pulled through openings in your home. The inspector would use a tool like a smoke pencil to detect where that air is coming from. On a windy day you can do the same thing.
Where are leaks typically found? Anywhere there is an opening cut into the home? Doors and windows are obvious but other areas can be at dryer vents, chimneys with leaky dampers, where the electric, phone, Internet, cable, water and gas utilities come through the wall, at electrical outlets and depending on how the house was sealed during construction, through the walls themselves.
Can a house be too tight? Furniture and many other household items can give off potentially dangerous gases if they are concentrated and you are exposed to them over a long period of time. We often speak of indoor air quality. What do you think new care smell is, or the smell of that new couch? If a home’s envelope is tight, an air to air heat exchanger can be added to make sure that air circulation is happening without replacing indoor heated air with cold air from outside.
Before you invest in expensive heating and air conditioning products or renewable energy the most important thing you can do is to make sure that the energy you are using isn’t leaking from your house or being conducted through areas with poor insulation. A solar panel installer I know tells all of his clients that before they invest in solar energy, they need to tighten up any leaks and add insulation. Solar is expensive and beyond most do-it-yourself types, fixing leaks and adding insulation is cheap and simple to do on your own. If you want to see how well you did, get a before and after blower test done and you’ll know that sealing leaks was worth the effort.
Also see: Home Insulation and Air Leaks