Blown in air duct sealing and individual run testing
My home has return air in the attic which is relatively accessible and supply air in the crawlspace, some of which isn’t very accessible. I had a blower door and ducting tests that revealed huge leakage. we applied mastic to everything accessible and fixed a big leak. We retested and got down to about 25% leakage and at the point the contractor said it was the best they could do.
The duct work is all metal with insulation. We have return air everywhere there is supply air and the home is 3400 sq ft. We have a lot of duct work. Tearing all the old insulation off to seal the joints seems excessive when I don’t really know what is causing the leakage. It may be in inaccessible runs most likely in supply areas.
Two questions; Does the spray-in duct sealing work? Second, Why cant mechanical contractors isolate the leakage side, supply or return, or isolate the individual runs? It seems a simple matter of pressure reading but what do I know?