Snowmelt with sand and pavers

8-ball

I've done a few snowmelt jobs with pavers over sand where the tubing is placed in the sand. All of which work fine, and incorporate a mixing device and heat exchanger for the snowmelt. It's been my experience that relatively high water temps are required in this application (150-170 deg)to get good performance. Because of the high temps I'm wondering if a mixing device is really required? Is there anything in that system that could be harmed by a potential 180 deg supply temp? I understand that tubing in concrete is a different story. What are people doing? Thanks