Whether you are a builder completing a new construction build or a homeowner with the goal of upgrading indoor comfort, you have probably heard of or have been recommended to conduct a blower door test. Most new construction builds require it to pass code inspections and it is a staple in the energy assessment arsenal to determine leakage rates. However, few people know how the test is conducted, let alone how to interpret the results after it is completed.
Put simply, a blower door is a powerful fan that is placed in the door frame of an exterior door using an adjustable metal frame and canvas covering. The fan is then placed in the opening of the canvas covering and a digital manometer (air pressure gauge) is connected to the fan to measure the pressure difference between the inside and outside of the home. After closing any mechanical openings in the building assembly such as windows, exterior doors, etc. and turning off any exhausting equipment such as bath fans and dryers as well as the HVAC equipment, the blower door fan is turned on so that it is pulling air out of the house until the pressure difference between the inside and outside is at the designated level, usually 50 pascals. Because the house is now under a negative pressure, air will pass through the building assemblies through leakage points, which can be identified by using a thermal imaging camera. This can help identify the locations and provide a roadmap for air sealing efforts.
A final reading of the blower door will also be recorded to do an ACH50 (Air Changes per Hour @ 50 Pascals) calculation. This calculation is done by taking the leakage amount of the house at 50 pascals, dividing it by the volume of the home, and multiplying it by 60. This tells us how many times the entire air volume of the home is replaced by outside air in a one-hour time span at 50 pascals. There are other calculations that can be used to determine envelope leakage rates, such as CFM50 per square foot of shell area (meaning the square footage of the walls, ceiling, and floor), but ACH50 is favored due to its simplified equation and takeoff requirements.
Once the results have been recorded recommendations for air sealing, fresh air ventilation requirements, etc. can be made. Most older homes will inherently be leakier due to outdated building practices, but modern building codes generally require homes to be 7 ACH50 or less to pass codes. Once a house is 5 ACH50 or less fresh air ventilation is no longer a recommendation but a requirement.
Schedule your diagnostic testing with E3 today to determine your home’s ACH50 and what recommendations are to be made to improve your home’s performance. Learn more about E3’s home testing and certification services here.
E3 Building Scientist Trent Performs Blower Testing on a Nashville Home
