Rusty heat ducts

[Tom Rees]

2002 house I inspected today. The basement heat ducts are run in the slab. This is a picture of rusty ducts. I thought there were specially designed metal ducts for this application. Any thoughts???

[Jim Luttrall]

2002 house I inspected today. The basement heat ducts are run in the slab. This is a picture of rusty ducts. I thought there were specially designed metal ducts for this application. Any thoughts???
Thoughts? Yeah, it is a stupid idea to put ducts in a slab. It is not common here thankfully but I have never seen ducts in a slab that did not have a moisture problem.

[David Bell]

Yeah,,Let's put steel ducts into a moisture rich environment and then ask why it rusts. Slab construction can be one of the most economical designs when done correctly, this one? not so much.

[David Bell]

One of the best slab systems I have seen was a UNICO high static system located in a closet with a sheet metal plenum and about 10, 2" pvc vents piped under slab to the outside walls, under windows. Return air was thru the closet wall which abutted the living room and had an Air Bear filter behind the grill. The condensate pump ran often and was a good barometer of how well the system was sized. These systems can be very noisey when not installed correctly, but this one was very quiet.

[Rod Butler]

Underslab ducts are not that uncommen but they should have been installed with a PVC coating. Having said that, back in the day we used to use them quite a bit before PVC coating but called for them to be encased in concrete. If the duct rusted out you still have a conduit for air.

AND, there is a significant difference between a catostrophic failure due to rust and just a few rust spots.