What is the purpose of this mixing valve?

[austin]

I guess this is a mixing valve, but I can't figure out why it's there. The water in these pipes flows toward the wall in this photo. The pipe on the left is a cold water pipe that goes to the garage only (it has a shutoff valve upstream from the photo). The pipe next to it coming out of the mixing valve is the only hot water pipe to service the whole house. The pipe on the far right is the cold water pipe that services the whole house (except the garage) and it also goes into the top of the mixing valve. The pipe that goes into the bottom of the mixing valve is the hot water pipe coming from the hot water tank. What is going on here?

[LazyPup]

It appears like it may be a form of a whole house anti-scald valve which is code required on systems which use the water heating source for both potable hot water and hydronic heating, in instances where there is an appliance (example,commercial dishwasher) which requires water at a temperature above 125 deg.F or mandatory by some local codes.

[HayZee518]

Lazy could it be a mixing valve for the toilet water to keep tank condensation down?

[LazyPup]

Hayzee,,,,I had considered that, but the post says the discharge side of this mixer is the main run of hot serving the whole house.

It is really difficult to be certain without seeing the valve closeup as it is not like most of the anti-scald valves currently in use.

Almost all of the anti-scald valves currently in use have a single control knob and an internal thermostatic action to maintain the hot water at a preset point, but prior to the introduction of the thermostic valves they made a manually adjusted "tempering" valve that constantly mixes a preset amount of cold water in the same manner as a tub or kitchen faucett mixer. The downside of the manual tempering valves is a wide variation in hot water temps from summer to winter as the cold water supply temperatures change.