Abandoned In Slab HVAC Ducts

[Wade Germann]

Good Evening everyone!

So I have a question for the greater BP population.

My home is a 1950s bungalow in Oak Lawn, which is about 30 mins SW of Chicago. I recently had my furnace moved into the attic due to some water leakage into our in slab HVAC ducts that we thought was coming from the old furnace.

So my question is this: now that the duct work is abandoned, what is the best way to seal the duct work off? 

I haven't come across a whole lot of information about this online, and opinions vary from pumping the whole duct system full of concrete, to putting spray foam in the ducts about a foot from each return and then filling the return with concrete in that small area so its capped off.

Just curious if anyone has any experience with this, or has ever heard of a contractor talking about this, etc etc etc.

Thanks!