I had my heating system, crawl space furnace and leaky poorly insulated sheet metal duct work, replaced a couple years ago with a 96% efficient system. The system was independently tested and certified. Flexible plastic wrapped duct work was installed.
Over the last year rats got into the crawl space, probably through a scupper damaged when the contractor installed the system condensate drain line. For some time my wife noticed drafts from the floor vents. I inspected the system and duct work and found a spot where a rat had chewed through one of 12 ducts. I taped the hole with aluminum duct tape and set out bait which dispatched the rats. I believe the duct work is adequately sealed because there are no musty damp crawl space odors emanating from the vents. The crawl space has always been wet due to ground water.
However, when I looked for and sealed gaps between the duct outlets and the floor there were still drafts coming from the ducts feeding each of floor registers . I plan to blow warm outside air into the crawl space to help dry it out and reduce the odor before I install scupper exhaust fans to keep it dry.
What are the possible reasons I'm still seeing the drafts from the duct openings?
If the drafts are due to other openings that I could not see, how can I find them?