I came across this configuration at an inspection that I have not seen before. Can anyone shed light on its purpose. See all 3 pics below.
Water heater on left serves an in-floor heat system, water heater on right serves the home.
The inlet of the house water heater (green arrow) is branched, goes through a backflow preventer, and what I believe is a pressure regulator (red arrows). The backflow preventer is vented to the floor (blue arrow).
After the pressure regulator, the branch is connected to the TPR valve on the water heater serving the in-floor heat (red arrow). What is the idea behind this configuration?