I'm looking for any input on the following condition:
1. Hot water heater is heated as a zone from my multi-zone oil heating system. There are two other zones, one for each floor. 2. Approximately 30 from the hot water discharge on the hot water heater (the pipes that eventually lead to the sinks and showers, not back to the furnace) there is an approximately 1/2" pipe that routes back to the cold water inlet side of the hot water heater. There is a check valve that lets the water flow the way I described it and a globe valve to cut the flow if desired. 3. All the piping in the house is that plastic stuff (the good kind, I already checked), not that I think it matters. 4. The furnace maintenance guy couldn't figure out what this does, thought the check valve was installed backwards and shut the globe valve. 5. I am on a well with a very small storage tank in the basement. 6. None of this looks 'accidental.' It clearly took some work and planning to implement this configuration.
Pause here to form your own opinions, as I'm about to type my thoughts.
There are two possible conclusions I was able to draw. 1. (Preferred) I think that this setup allows some of the hot water from the discharge to act as a 'preheat' for the water coming into the tank to minimize the thermal stresses on the internal hot water tank components when well-temperature water hits the tank during my morning shower. Minimizing the thermal stresses extends the life of the tank and would be 'good plumbing' installation practices. 2. I think that this setup allows for some natural circulation during idle periods to allow the tank to heat up and cool off continuously so that the furnace gets a workout more often during the summer. The hot water in the pipe cools in the basement, gets heavy and displaces hot water in the tank, forcing more hot water out, etc. While possible, I can't see the water as having enough head actually do any work and I also don't see the advantage to running my furnace more often than necessary to keep me in hot water.
If you have some thoughts, or even better, some facts, please comment.