I had a recent geothermal install, which included the installation of a buffer water tank attached to the desuperheater.

They did not install any drain pipe to the P/T valve on the top of the tank though. (If the valve opened, it would just start spraying or leaking from the middle of the top of the tank.) Is this an acceptable practice, or should I have them come back and add a drain pipe? (My water heater, which was here before the geothermal installation, has a drain pipe on it's P/T valve. It drains to the sump pit.)

Thanks.

My inspector made me install the drain pipe. His argument was if the valve is there it could actuate and spray water over the electrical components (the geothermal), didn't matter to him that the tank was inactive and not wired up. All I needed was the drop pipe as the floor is concrete and has a drain, and I wasn't going to argue hard, no point in pissing off the inspector for a couple of parts and 2 minutes of work.

A P/T valve is required when there is a closed vessel and a source of heat. If there was no isolation valve between the buffer and the finish tank then a P/T valve may not have been required. However once a P/T is present the downpipe is a must.

Further if you have "throttling valves on both sides of your DSH then the P/T valve likely should be there (between the stops), but most inspectors aren't savvy to that.

Hmm. No one ever had an inspector come as part of the job (which involved installation of the closed ground loop, a fair amount of duct work, the HP unit, the buffer tank, related plumbing, etc.) Should I have gotten an inspector? Should the contractor have? Or are we good? Thanks.

The work you describe is invasive enough that many jurisdictions would require permits and inspections. Now my ground loop didn't require any inspections, but the plumbing and electrical hookups did, as would any structural work done as a result of modifying the ducts. My county also requires that the correct modeling (Manual J, and if needed D) have been done to verify that the equipment is sized correctly. Some folks would complain that this is an example of government overreach, however that is not the intent, the intent is to protect the consumer. In my case I did all my own work, I'm allowed to do that here, not everybody is (and in that case I might be complaining of overreach), and I found the inspectors to be more than willing to work with me. Of course it helps if you know enough that they don't have to babysit you though the whole process. Unfortunately, at this point I don't know what you should do. My county has a procedure for inspecting and allowing unpermitted work, however the process would likely damage your relationship with your installer (they assume that the homeowner is not required to know better, but the installer is). However the missing drop tube begs the question is there anything else that has been shortcutted.