Testing ducts for leakage is probably one of the most important functions we can provide. Duct leaks can account for almost half of your cooling/heating loads. In hot Florida summers this can mean big savings to you.
To test duct work we temporarily seal off every supply and return in the system. We then hook up a small fan to one return, and pressurize the ductwork to 25 Pascal’s. To maintain a steady pressure we know that all the air entering the system must be escaping through leaks. Using the manometer, we can see how much air in cubic feet per minute is being pushed into the system. We have seen ducts leak more than 75% of their designed air flow!
Now leaks are never good, but some are far worse than others. Ductwork may run above your first floor ceiling, and leak to your second floor. You may have leaky ducts in a wall where the leak enters the room through a switch plate. These leaks are considered leaks to conditioned space and cost less, but can create comfort issues in rooms that are short changed.
Measuring leakage to outside conditioned space requires a blower door in addition to the duct blaster. The blower door is set now to pressurize the home to 25 Pascal’s while the duct work is being pressurized to the same 25 Pascal’s. Now any leaks to conditioned space is canceled out by the blower door and the duct blaster will only show leaks to unconditioned space! Once the measurements have been made we can decide on an approach for repairs.
Typically we will always try to seal leaks closest to the air handler as the pressures will always be highest at these areas. Near the handler, a hole that measures 1/8 of inch wide may leak 15 times as much as the same hole near the end of a run. Ultimately, we would always want to seal up the ducts so that the leakage measures zero, but in real life it is usually unpractical.
BPI has set standards; typically we can allow no more than 10% of the verified system flow in a total loss test. This is what we try to achieve on every job.
If you have any suspicions that your duct work is leaking, stop throwing your hard earned money out the window. Duct maintenance is one of the most important heating and air conditioning repairs you can make.