I'm in the process of replacing my Apollo Hydroswirl water heater. It uses hot water run through a heat exhanger to heat our house as well. Finding this exact heater has been a big challenge already.
Anyway, in looking at the piping to get familiar with how it was installed and determone if I would attempt to plumb it myself (leaning towards not due to the extra functions of water going to the heat exchanger), I noticed this little regulator/valve thing mounted just out bound of the heater and actually connects the cold water inlet and the outgoing hot water line. I'm guessing an expert will be able to quickly identify it's purpose and proper name, I'm just curious because it looks like it's actually adjustable as well.
Can someone explain what this is all about. See PICS below.
Thanks,
John :)

The leftmost picture is a mixture valve which is indeed adjustable and should have marks on the knob such as 1, 2, 3, 4 or whatever to indicate output temperature.

It adds cold water to your hot water for the faucets so you don't get scalded.

It does not alter your baseboard heating temperature (follow the pipes to confirm).

If desired, adjust it by turning knob and attach a note to it stating something like mine:

1 = warm
<---- hot enough
2 = hot
3 = hotter
4 = hot hot hot

I am no expert but I found out about it and had one installed after being hot hot hotted once or twice.

Sounds reasonable but I don't know why you would cool your just heated water coming from the water heater.
Can you give me a little more detail as to how/why this is a desirable?:confused:

The Temp of the water coming out of the heater is not safe for bathing or use in the kitchen so the cold water is added so that the temp will be lower at the shower and sinks.