How a Duct Leakage Test Works:
First, you need to determine if a duct leakage test is required. The only time duct testing is required is when parts of the HVAC system are outside of the conditioned envelope. This includes areas like unconditioned attics, garages, and crawlspaces. If any supply or return duct chases, flexible lines or air handler units are in these areas, by IECC 2015 code, a duct leakage test is required. If a crawlspace is conditioned, then no test is required.
A duct leakage test (duct testing) can be performed at rough-in before drywalling, or post-construction. In both cases, the requirements are the same. The system will need to achieve a leakage rate of less than 4 CFM (cubic feet per minute) per 100 square feet of the home. Here is an example:
40 CFM moving through the ducts when put under pressure.
1000 sqft house.
38CFM / 1000sqft = 0.38 x 100 sqft = 3.8 CFM
This is commonly referred to as a 4% leakage rate.
Duct Testing Process:
Testing the ducts requires sealing all the openings of a duct system. This includes all supply and return registers. We do this by using large HVAC tape to cover and seal the openings. This process can take some time as we try to create the best seal possible. Our fan is then sealed to the air handler or a large return opening.
The fan is run to depressurize the duct system to -25 pascals. The amount of air moving through our fan is then measured. The number generated under 25 pascals of pressure is known as [email protected] This CFM number is the number used in the calculation.