Out of curiosity gentlemen, when you pipe a 3 way into the boiler loop to serve a floor, what happens to flow in that loop when the zone valve for the floor opens? 8 loops for example, 2400 sq ft, average insulation, we're looking at 4-6 GPM necessary to properly heat said floor with tempered water. The typical 1" PEX underground can only carry 7 GPM total, so you have 1-3 GPM or 10-30k BTU left in your main loop. Mama's doing laundry and needs some hot water or all 4 kids run through the shower; there goes whatever was left. Then your forced air calls or the unit heater in the garage calls; oh dang, there's nothing left, why not? It'd be different if a radiant floor only ran for 5 minutes like forced air does, but with proper water temps a floor will run for several hours straight, robbing 2/3 of your available BTU. Being separated with a plate, that floor only uses its own water to heat and passes it through the exchanger to heat it instead of physically using the boiler's water to circulate through the floor. This maintains a constant 7 GPM through the boiler loop regardless of load, and allows it to replenish several times faster while still keeping everything satisfied. I specialize in radiant floors and have yet to see an atmospheric system perform anything like a closed when there are other things in the loop. It's not that I'm closed minded, I really would like to see an atmospheric system prosper to simplify the installation process but the fact is that it doesn't. Even if the floor is the only thing in that loop, a guy still needs a 4 way mixer or at least a 3 way zone valve plus a 3 way mixer to get flow without deadheading the boiler pump right? Perhaps I'm missing something but of the dozens I've swapped to closed, exactly zero of them performed worth a crap the other way and I can't see how they could