Replacing a rat urine damaged heating duct that runs betweeen floors.

We had rats for a while. Didn't realize it until smell of rat urine coming out of heating vent in our kitchen became obvious. Now my problem is getting rid of smell.
Smell may be coming from soft duct that runs for about 17 feet from furnace. Fourteen of these feet run between floors. I don't know how houses are generally built. Access to this duct seems to me would have to come from above (thru kitchen floor) or below, thru lower level ceiling. In my case, going thru ceiling would be far easier. Is this the best path to a duct that runs between floors? Through a ceiling from below? I imagine I could possibly pull duct out from furnace area, but believe that I would have to access area to replace it.
My other problem, is that smell may be coming from damaged wood etc. and not duct. What are the layers below my kitchen floor? It looks like 6 inch tiles, but grout area is too smooth to have been put down as individual tiles. Looks like a prefabricated "tile" floor. Maybe 1/4 inch or more thick. Then comes a subfloor? Then 2x6s? Ducts would run between these? Then a ceiling below? So if I remove sheet rock type ceiling, I could access duct, and possibly 2x6s?
Let me know. Thanks

 

Hi Douglas,Yes thats the best way to access the ducts.Its alot easier to replace the drywall you remove,then to replace the flooring and any sub-flooring you might remove.Under your sub-flooring you probably have 2x10's for your floor joist,not 2x6's.Your duct work runs between your joist.Your going to have to cut enough drywall out to where the duct is connected to the floor vent.

Good Luck