I had every connection painted with a mastic paste that hardens up. Seems to be better than nothing. Also noticed that I can smell the pine lumber roof trusses after 15 yrs of use. Must have some small leaks. Possibly on the intake side. In fla this might be a worthwhile fix.
I made a phone call to my nearest dealer for the product and they will be at my house November 24 to give me a free estimate. I have two A/C systems in my home. They have a way to show you exactly how much your duct work leaks.
The duct system isn't really the problem . Home hvac systems run about a half pound of static pressure . Air takes the path of least resistance . Half pound of static isn really enough to push air out the seams or slip and drive connections . The duct sealers are going to pump about 10 pounds in the system and yea it's going to leak down . The main air loss / gain is the plenum / unit connection , unit / coil connection and return / unit connection . Does the seal company spray crap in the return also ? I would not recommend that as if it bypasses the filter and gets on a water or AC coil ....how do you seal the doors on the unit ? Glue them shut ?
I used duct tape to seal all the joints in my pipe connections or where there were holes in the pipes. Back in Michigan out in my barn I wrapped insulated wrap around the exposed pipes then wrapped them in fiberglass insulation to help keep the heat in the pipes so I got a good war flow out of the registers. Bet all that is still cheaper than that aerosol.
I used to work in HVAC before I startedmy construction business. I always used a heavy duty foil tape like ployken 339. It is code in Michigan now to seal every connection in the duct system. I also find it funny that duct tape is against code to use on new duct ststems