Four Way Thermostatic Mixing Valves

[bauer0667]

Anyone have any experience with a setup like this? The goal is to get the return temp of the boiler above 120 Degrees.

 

[koditten]

Look up close spaced "tee's". Very common for using a boiler to heat floors. It how my system is set up.

 

[TurnipTruck]

More than everything you will need to know is available for free online in the Caleffi series of illustrated technical magazines.

Caleffi.com
Idronics

I went with a hydraulic separator, but the closely -spaced tees primary/secondary loops would be cheaper.
A thermostatic three-way boiler protector loop may be all you need if your emitters are high temp like a baseboard.