Fixing gaps in heating ducts

[paulam2]

I have a 35 year old house that is half-slab, half-basement. In the basement, there are several places where there are gaps between pieces of duct, and they don't join up. The ducts are right up again the (basement) ceiling, and it's difficult to impossible to get around them to put tape around them. Then, where the ducts run into the slab, there are pretty big gaps between the metal ducts and whatever material runs through the slab (looks like plastic or fiberglass?), and there's no way that HVAC tape is going to seal these gaps. Is there anything else I can do to fix these kinds of gaps?

[Ed Imeduc]

Not sure what you have there. But get some sheet metal and cut it so its wide enough to cover the open part and lap on each side . Sheet metal screw it on then cover the whole patch and edges with the duct mastic.

ED ;)

[heatpumpman]

It can be a mess to work with but if applied slowly and deliberately it can work like nobodys business.

[danski0224]

There are commercially available duct sealers that work well. The water based ones do not smell so bad, but do not fill the larger gaps so well in one application.

The solvent based ones will knock you out without ventilation.