Blower door testing is the most practical way to predict energy savings from air-sealing methods.
Compare blower-door operation to inflating a leaky beach ball. When you inflate a beach ball, it doesnâ€™t take much effort to fill it if there are no holes present. If the ball has a few pin holes, you have to apply a little more effort because eventually the air will leak out and the ball will become deflated. If there are holes that are bigger (such as raisin-sized holes), you will have to put forth an incredible amount of effort to keep the ball inflated. The total size of the all the holes and the pressure difference between the ball and the outside determines the rate at which you need to blow air to keep the ball inflated.
Like the blowing pressure of your lungs to keep a beach ball inflated, a blower door pressurizes your home by blowing air in or depressurizes the home by sucking air out. Depressurization, which creates a vacuum indoors, is the most common procedure because air comes in through air leaks, allowing you to feel and locate the air leaks in your home. The combined area of the building leaks and the pressure difference between indoors and outdoors determines how much air the blower door moves. The air flow is measured by CFM (cubic feet per minute). The standard for measuring a home’s air leakage is the air flow through the blower door at 50 pascals of house pressure (CFM50)
Blower door testing involves preparing the home for testing, setting up the blower door in a doorway, connecting the gauges, turning on the blower door, and reading the pressure reading on the gauges.
Prepare for testing by following these steps:
- Close windows and storm doors.
- Open all interior doors.
- Disable heaters and water heaters by turning their thermostats down.
- Cover ashes in wood stoves and fireplaces with damp newspaper to prevent them from being sucked into the home.
- Shut fireplace dampers, fireplace glass doors, wood stove dampers, and wood stove air intakes.
The blower door operator should slowly bring the house pressure to 50 pascals. This is usually preset with the blower door gauges before he begins. With the house pressure at 50 pascals, the operator notes the CFM50 number from the digital air flow gauge. Then he begins to look around the home with a smoke generator to help find the air leaks in your home. I promise that you will be amazed to discover where the leaks are and the amount of leakage that occurs.
There are several common factors to help to determine the amount of air leakage you may have in your home. This is a little technical, but it will help you to understand the importance of a test of this nature.
- The 50 Pascal Airflow Rate: a blower door reading expressed in cubic feet per minute (CFM50) is the actual flow measured at 50 pascals of house pressure.
- The 50-Pascal Air Change Rate (ACH50): a blower door reading expressed in air changes per hour at 50 pascals. This is calculated by multiplying the CFM50 by 60min/hour and then dividing by the house volume in cubic feet.
- Natural Air Change rate (ACH natural): natural air change is expressed in air changes per hour.
If all of this seems a bit overwhelming, the home energy auditor in your area will know just what to do with all these numbers and formulas. If you are wondering where to find an energy auditor, check with your local courthouse or utility company. Hiring a home energy auditor will be money well spent!