Blower Door Testing
Some of you may have heard of a blower door test but most have not and few have ever seen one done. My goal with today’s column is to explain what a blower door test is, why it’s important to home owners, how a test is performed and what the test results mean.
What is a blower door test?
A blower door is a large powerful variable speed fan that is installed in an adjustable fabric frame designed to be installed in a residential door opening. The fan sucks air out of the house, essentially depressurizing it. The door is equipped with a gauge (manometer) that displays the difference in air pressure between outside the home and inside the home (50 pascals of air pressure differential is typical for testing, equal to a 20 mile per hour wind blowing on all sides of the home) and the cubic feet per minute of air being exhausted from the home (CFM/50).
Why is a blower door test important?
Air flow through a building can have a powerful impact on comfort, indoor air quality and utility bills. Blower doors provide a way to quantify air flow and the resulting heat loss, along with a way to pin point specific leaks. There use in retrofit work allows both instantaneous feedback and quantitative inspections. Uncontrolled air loss from a home can have a significant impact. Typically air leakage can account for as much as 25% or more of a home’s heat loss, i.e. higher energy bills. Nearly all government and utility founded energy saving programs require a blower door test.
How is a blower door test performed?
The blower door is installed in an exterior door opening that allows the greatest air flow from the rest of the house. All other doors and windows are closed and locked. All interior doors are opened so air flows easily thought the house. If the basement and/or crawl space is within the thermal envelope (directly or indirectly heated) all openings to those spaces need to be opened. All intentional openings are to be left in their normal operating condition (bath fans, range hoods, furnace/boiler chimneys, dryer, etc. All fires must be out in fire places and wood stoves and all fireplace openings are sealed to prevent scattering of ashes throughout the home (I learned this the hard way). All combustion appliances are adjusted so they don’t turn on during the test. The blower door fan is turned on and adjusted to 50 pascals of pressure differential between indoors and outdoors and the cubic feet of air per minute (CFM/50) exhausted from the home is recorded.
What does the blower door result mean?
When the blower door test is completed we take the data from the gages together with the homes information (volume, floor area, surface area, number of bedrooms, number of occupants, wind shielding and weather conditions at the time of the test) and enter all this data into a computer program which provides us with a Building Air Tightness Test Report.
Below are listed three of the reports with a description of what they represent and what the number would be for a tight house, a moderately leaking house and a very leaky house. Keep in mind that the leakiness numbers listed should only be used as a guide and may very greatly depending on many specifics of the house being tested.
CFM/50: The flow, in cubic feet per minute with a 50 Pascals of pressure difference between inside and outside the house.
Tight houses tend to be less than 1,200 CFM/50
Moderately leaky houses 1,500-2,500 CFM/50
Quite leaky houses over 3,000 CFM/50
ACH/50: The air changes per hour at 50 Pascals of pressure difference between inside and outside the house. Air changes per hour, a description of leakage as compared to house air volume. The number of times each hour an amount of air equal to the volume of the house leaks out. Used for both blower door measurements and estimates of Air Changes Per Hour @ Natural (ACH/N).
Tight houses ten to be less than 5-6 ACH/50
Moderately leaky houses – less than 10-15 ACH/50
Quite leaky houses – over 20 ACH/50
ELA: Effective leakage area. The area in square inches of a hole which, with 4 Pascals pressure difference, leaks the same amount as the house. In other words if all the air leaks in a house were put in one place the hole would be the size of the ELA.
Tight houses tend to be less than 144 sq. in. ELA (12”X12” hole)
Moderately leaky houses have less than 324 sq. in. (18”X18” hole)
Quite leaky houses are over 576 sq. in. (24”X24” hole)
Max Strickland has been involved in the construction industry for 44 years. He is currently a principal with Strickland Ewing & Associates providing Building Performance Consulting, Green Building Green Building
No comments:
Post a Comment