Hello. I am building a new house, a ranch style with radiant in the concrete basement floor and under the subfloor for main floor. I plan on using a condensing boiler with an indirect hot water tank. Now, my issue involves the different temperature requirements of the two different radiant applications. In a house I built 9 years ago, I just used a Slant Fin direct-vent cast iron boiler with two manual mixing valves to mix down the temperature for the basement concrete slab and the under-subfloor heat. No outdoor reset, just two thermostats. Did run the boiler at only 160 degrees, always had plenty of heat.

With my new system, I want to take full advantage of outdoor reset and lowest possible boiler temperatures. With manual mixing valves, the temp in the loops won't go below the setpoint of the mixing valve, unless of course the boiler temp goes below the setting of the mixing valve. To do it correctly, I find that I will need a mixing solution that will also take advantage of outdoor reset. As I see it, the best ways are to either have two seperate injection pumps or two controllable mixing valves for the two different temperatures required. Am I correct? Any other suggestions? I am finding that the controls for dual injection systems can be quite expensive, 30 to 50 percent the cost of the boiler. Taco makes a nice mixing valve that connects directly to an outdoor reset. Many condensing boilers have outdoor reset and DHW priority built-in. None have mixing valve/injection pump controls that I know of. Would the Taco mixing valves with built in outdoor reset be a better option than a Tekmar control or similar control?

Thanks for any help,
Mark