Total duct leakage vs. outside leakage test….
I’m in Florida. I have a question to get some real-world feedback on duct leakage from those who are RESNET and/or BPI raters and have experience with duct blaster and blower door testing.
When testing both duct tests. In this example I have questions on….. Can you have a largish difference between the two tests results? Meaning a qn of 0.04 for the outside leakage test and a qn of 0.14 for the total duct test based on square footage for both tests? Does this 10 point spread seem extreme to anyone?
Is there some sort of industry norm spread between the outside leakage and total test?
The reason I am asking here online is, I saw the results on a 1480-square-foot home with a lot of registers/grilles…but they would be the only “ductwork” in the conditioned space. The fan-coil and rest of the ductwork was in the garage and attic or the uncondtioned space.
So I am assuming even thought the registers are taped up, they still will leak between the drywall ceiling the grille edge and side of the grille edge unsealed corners? The ceiling boxes or register boots were sealed with mastic to the top of the drywall, so they couldn’t leak there.
What seems odd to me is the spread could be that far apart? Although the house did have 1-2 supply grilles in every room and 1-2 returns in every room as well. So can there be this much leakage from the registers? Has anyone seen this kind of spread between the two tests?…Is a largish difference pretty normal in some regards?
And I understand each house/ductwork system will be very different from one another…but any feedback would be appreciated. Thanks!
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In my testing, I typically do not find much difference between total leakage and leakage to outside when the ductwork and air handler are outside of conditioned space. That said - I tape over the entire register and seal to the drywall and/or floor....and cross my fingers that the duct mask doesn't pull the paint off upon removal.
Could it be that your garage it somewhat "connected" to the interior of the house and not entirely "outside" of the thermal envelope?