Here are some common areas you can access for sealing. NOTE: These are all much easier to access BEFORE drywall… And many are completely unnecessary if you do not use returns for cavities (which is no longer legal per MN State Energy Code).
This is the front of the cabinet, the box where the A/C coil lives. It is a nice gasketed box made for easy access for techs, but if you need to pass the test, sadly you will need to tape this up. Notice also the seams above. Tape all seams!
This one of two larger returns, looking from the bottom up into the cavity. Above the duct itself, you just see a block we made to seal the cavity. Now the duct pulls air just from the living space and not from the wall.
Up inside the return cavity, the electrician’s run. You can reach up to foam in the hole. But please notice the unsealed gaps along the front and back of the cavity – sadly this duct will never pass the tightness testing.
Imagine the duct system like a plumbing system. Every crack that water could leak through, air can leak through. Now, just like your plumbing system, the air system is tested for leaks, so please seal up those cracks.