Duct Tightness Testing (Duct Leakage Testing)
(Duct Blaster Testing)
Sealing ductwork requires finding the leaky joints and sealing them with Mastic, a compound similar to spackle, except it is higher heat rated and better at sealing gaps in ductwork. Another option is to use HVAC rated aluminum foil tape. Note that not all aluminum foil tapes have the same quality and some will fall off your ducts within a few weeks if it is not HVAC rated. Not every town accepts HVAC foil tape for ductwork sealing, so check with your local code enforcement official. Note the picture on the left, they missed several joints. For using mastic on the right, the mastic must be about as thick as a nickel to be effective, so avoid any installer who just does a quick brushing-on.
There are more than a million miles of ductwork in U.S. homes, and industry experts estimate that more than two-thirds of them are leaky enough to justify sealing or repair. Leaky ducts can significantly increase air conditioning and heating bills, dramatically reduce equipment capacity and performance, as well as result in potentially dangerous indoor air quality problems. In fact, duct leakage is responsible for many of the comfort issues experienced by homeowners today.
Why Is Duct Leakage Important?
Leaks in forced air duct systems are now recognized as a major source of energy waste in both new and existing houses. Studies indicate that duct leakage can account for as much as 25% of total house energy loss, and in many cases has a greater impact on energy use than air leaks from the attic. Just as important, duct leakage can prevent heating and cooling systems from doing their job properly, resulting in hot or cold rooms, and humidity problems. Worse yet, duct leaks can create air quality problems by pulling pollutants and irritants directly into the house.
Measuring Duct Leakage
A duct leakage performance test involves pressurizing the duct system with a calibrated fan and simultaneously measuring the air flow through the fan and its effect on the pressure within the duct system. The tighter the duct system, the less air you need from the fan to create a change in duct system pressure. Testing procedures can be set up to measure only duct leaks which are connected to the outside, or to measure total duct leakage (i.e. leaks connected to the outside and inside of the house). Duct leakage measurements are used to diagnose and demonstrate leakage problems, estimate efficiency losses from duct leakage, and certify the quality of duct system installation.