You’ve been in the attic, the crawl spaces or basement, climbed up and down any stairs several times. The have been some questions from the home owner and perhaps from the kids in the house. If you are like me, you’ve bumped your head a few times on low hanging fruit. It has been a fun, rewarding and perhaps a little stressful.
The thing I do to relieve this stress, is to depressurize. Yes, let all that built up stress just flow out the door. It’s not Yoga, or some mystic belief in spiritual forces. It is the wind and the open door.
I set up the Blower Door and depressurize the house. The air moving past me, goes out the fan, and the stress goes with it. I just have to let it go!
Now you know one reason why I leave the Blower Door until very close to the end of the audit. Now questions may pop into your head. Why a blower door test? Why depressurize the house? What is the reading of the test? Is my test good or bad? How much better a reading is my new house, than the old house my friend lives in? What can I do? What does it mean?
Ahhhh! Those are all good questions and they are ones that I get asked regularly. What is the Blower Door and what does it test for? The Blower Door consists of a fan hung in a nylon insert that is held in a temporary frame placed in the front door. The fan moves air from the inside of the home out. It measures a pressure difference between the inside and the outside. It also measures how much air is being pulled out to create that pressure difference. As the Blower Door is pulling the air out, it blows past the Energy Auditor, and I get depressurized as well!
The blower door is used to test a home, or a commercial building, to determine how much leakage is going on. You have probably felt a cold draft in the winter somewhere in a home. Some of the drafts are fairly easy to locate, such as under a door. Other places that leak air are not as easily found. Leaks do not need to actually enter the room to cause a problem. If air leaks into the wall it can soak the heat right out of the room.
The Blower Door simulates a 20 mph wind on all 4 sides of the house and the roof at the same time. If the wind is blowing on the outside, the way to simulate that effect is to place the fan to pull the wind out of the house. By controlling the amount of pressure difference between inside and outside, the Blower Door can tell you about how your home keeps the air fresh. It will show you where the fresh air is coming in.
The air is coming into your home with all the doors and windows closed, can be correlated with the size of the home and an amount of leakage determined. It is also important to record the inside and outside temperatures during the test. Some temperature differences can change the test results. In the winter, the cold air outside has more density then the warmer air inside. The leakage will behave differently if you have a hot summer day with the temperature outside at 95 or higher.
Many people say your house needs to breathe. I don’t think so. I think the life in your house needs fresh air. How you provide that fresh air is your choice. Your home should change the air about every 3 hours to provide fresh air, for those live things in your home. Live things would include plants, pets, and people. Cooking, especially with a gas range, showers, the typical gas hot water heater, and a typical gas furnace also require fresh air. Providing fresh air is one step, providing quality fresh air is a second step. Both should be taken at the same time.
What is the reading of my test? Is my test good or bad?
Energy Auditors and Building Science types, refer to the results of a blower door test as “XXXX CFM at 50”. The test is standardized to depressurize the home to a difference of 50 pascals with relation to the outside. CFM is for Cubic Feet per Minute. The measure shows how many cubic feet per minute when depressurized to a difference of 50 pascals.
What is a pascal and how much is it? A pascal is a metric unit of pressure. It is not much pressure Here is the US we like PSI (pounds per square inch) or water column inches. Some of us are familiar with a bar, or an atmosphere, or a Torr. (You can read Wikipedia to learn about those! I did! ) 1 water column inch is 250 pascals, or about 0.03 PSI.
This image of my manometer is reading 45.2 pascals with a flow of 2552 CFM.
So is my test good or bad? It is not good or bad. It is just a score. It gives a measure for your Energy Audit to determine how much the uncontrolled air exchange in your home costs in Energy Bills, and how much we can reduce it for what price?
The air leakage can be evaluated by the volume within a home. It can also be evaluated by the size of the walls and the ceiling. Until those numbers are calculated to go with the reading, it doesn’t mean much.
How do I compare to a house down the street? That is not comparing apples to apples. The house down the street is different because a different family lives there. They have over a few or over many years, modified the house. How well have the inside walls been maintained, how many coats of paint. One of the homes I tested with the least opportunity to save on Energy Bills was built in 1912.
What can I do to reduce the uncontrolled leakage in my home.
You can become a caulker! Not a clunker! Caulk or something hard that you can not blow through stops air leakage. Insulation, most types, you can blow through does not stop air leakage. Where to caulk is a different story and deserves its own post on the blog.
Thanks for reading! Thanks to @splintergirl for the idea!