Sealing heating duct openings through floor to reduce radon?

[Rob]

Anyone have any good ideas on what to use to seal the openings that was created for the heating registers installed on the first floor. There is about a 3/4'' gap around the register looking up at them from the basement.Can I just foan it up with latex expanding foam. I wasn't sure how the thermal expansion of the heat duct would effect this or if it is against code. I suppose I could just tape the gap with hvac foil tape, but I prefer a more permanent solution. I'm trying to control radon migration thru the basement ceailing by sealing all holes thru the OSB subfloor that were made by the various contrators.

[B]

If the house is new, the contractors were required to seal the holes with fireproof caulk. Great Stuff

is a pretty permanent solution. Apply it slowly because it expands a lot and you want to see how much is really needed.

[CBhvac]

Firestop is required, and foam isnt that. You will need a tube or two of the firestop seal.

Now...if you have a radon problem, you need to concentrate more on the removal of the radon from the basement, since you wont stop it from making its way into the home.