Three Reasons Why There Is No "Inside Duct Leakage" Test
In the HVAC world, ductwork is installed, sealed, and tested. A couple of these tests performed fall under the category of duct leakage tests. The contractor or technician is looking for leaking air and loss of pressure, both of which are important to the efficiency of your heating and cooling systems. There is the outside leakage test, which looks for air leaks outside the "house envelope," or just outside of the house and its foundation. There is also the total leakage test, which looks for the total loss of air pressure and air leaks. However, there is no inside leakage test, and here is why.
Leaks Inside Stay Inside, and That Is Okay
If cool or warm air leaks out of the ductwork inside your home or building, that is an acceptable loss because it is inside. It is not being wasted, really, since the cold or hot air is cooling or heating a little bit of space where the small leaks are located. Because the cooled or heated air is not escaping to the outside, there is no real need to test it or count it as a loss.
It Is Difficult to Measure Leaks Inside When the Inside Air Is the Same Temperature
If you have a small duct leak inside, the air leaking out is the same, or close to, the temperature in the building or home. It would be really difficult to test for indoor leaks when there is no major temperature differentiation between the indoor air and the leak of air coming from the ductwork. A measurement of the leaked air would produce skewed results because of the surrounding air, and there is not much that could be done about it.
The Total Leakage Test Already Reveals the Leaks and What Is Lost
A total duct leakage test gives you a bigger number relating to pressure, heat, or cooled air lost. When the technician finds the outside leak test number/results, the outside leak number is subtracted from the total leak to give you an idea of any losses inside. Hence, having a completely separate test for indoor leakage is redundant and not necessary.
Making Sure Your Ducts Do Not Leak
You do not want the ducts to leak to the outside. Minimizing this maximizes your furnace's and your A/C's energy because they do not have to constantly turn on to make for the losses going out the window, figuratively speaking. The technician does all he/she can to seal and cover ductwork so that the highest possible percentage of air and pressure remains in the ducts and travels up into the building/house where it belongs.
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