I was on a service call today and looked at their heating set up. Sorry for the bad picture. All I had was my phone and it was dark. One supply and return manifold. No mixing valves. I should have looked to see what the boiler was set at. They had HWB and radiant under joist and in concrete. I didnt see any boiler protection on the return side done either. The lay out was organized. Seven zones and a pump for each one. They all had flow checks on the supply side. There were shut off valves on both supply and return side withe boiler drains about to drain from both ends. This wasn't a P and S system. Only the manifolds that you see. So when one of the zones opened it would kick on the circ and push water through everything back to the boiler.