I'm a Home Inspector, neither a Tech nor a Homeowner, hopefully this is the right forum. I'm trying to confirm what an HVAC Tech told me to make sure it's correct and I currently don't have an HVAC source that I know and trust. I recently inspected a House where the ducting is below the slab. The air temperatures that I measured at the various vents dropped off significantly as I got further from the Unit, in some cases as much as 30 degrees cooler when heating and 12 degrees when cooling (it's a big house with 5 zones). These measurements were taken after running the system for 20-45 minutes. I figured that the ducting was original to the house (40 years or so old) and may be rusted out. The tech said that the ducting is buried in the ground 3-4 feet and it takes 3-4 hours for the temperatures to equal out. In ground ducting is fairly rare around here so I don't see enough of them to have a good feel for this. Is the tech right or is this cause for concern?
If there's any question about the integrity of the system what if any tests can be done to determine the health of the ducting?
Is there any fix for in ground ducting if it is leaking or rusted out?
Thanks very much for any help that you experts can offer with this, I don't want to report something like this as a problem if it is not.