Are you building your own home or adding an addition to the house? Homeowners acting as their own general contractor may be required by code to have a 3rd party duct pressure test. This requirement applies when constructing new homes or in a retrofit situation when the duct system has been installed in an unconditioned space such as an attic, crawlspace, or garage.
Why is Duct Tightness Important?
- Because indoor air travels through duct work that is prone to leak, placing ducts in areas that are outside the conditioned space can result in a loss of conditioned air to the “outdoors.” Studies show that a typical duct installation loses 20 to 30% of the air before getting to the registers. If that air happens to leak outside the building envelope, comfort complaints and high utility bills will likely result in callbacks.
- Ducts located outside the conditioned space of the home can pressurize or depressurize the building when the air handler is operating which results in increased air leakage through the building envelope.
- Duct pressures can bring pollutants into the indoor air from areas like attics or crawlspaces. These pressures can even interfere with the venting of natural draft water heaters and furnaces.
- Within the home itself, unbalanced air flow from duct leakage can pressurize or depressurize zones in the home and cause comfort complaints.
How is the Duct Pressure Test Performed?
- Using a special duct mask tape, the system is temporarily sealed off at all supplies and returns. Note: at the rough-in stage, registers and grilles do not need to be installed to perform the test.
- Using the Minneapolis Duct Blaster from the Energy Conservatory, we will hook up the fan at the air handler. If the air handler is not yet installed, we will test the supply and return sides of the system independently and add the 2 leakage totals together to determine the total leakage.
- The total amount of leakage in the system is determined by pressurizing or depressurizing the system with the Duct Blaster to 25 pascals (which is equal to 0.1 inches of water column).
Professional energy auditors use blower door tests to help determine a home’s airtightness.
These are some reasons for establishing the proper building tightness:
- Reducing energy consumption due to air leakage
- Avoiding moisture condensation problems
- Avoiding uncomfortable drafts caused by cold air leaking in from the outdoors
- Determining how much mechanical ventilation might be needed to provide acceptable indoor air quality.
How They Work
- A blower door is a powerful fan that mounts into the frame of an exterior door. The fan pulls air out of the house, lowering the air pressure inside. The higher outside air pressure then flows in through all unsealed cracks and openings. The auditors may use a smoke pencil to detect air leaks. These tests determine the air infiltration rate of a building.
- Blower doors consist of a frame and flexible panel that fit in a doorway, a variable-speed fan, a pressure gauge to measure the pressure differences inside and outside the home, and an airflow manometer and hoses for measuring airflow.
There are two types of blower doors: calibrated and uncalibrated. It is important that auditors use a calibrated door. This type of blower door has several gauges that measure the amount of air pulled out of the house by the fan. Uncalibrated blower doors can only locate leaks in homes. They provide no method for determining the overall tightness of a building. The calibrated blower door’s data allow the auditor to quantify the amount of air leakage and the effectiveness of any air-sealing job.
