I have three new mixing pump secondary loops to install along with the Garn, all in slab. I have a Tekmar 363 and 362 currently running the radiant in concrete in the house and staple up (second floor, though haven't installed the tubing yet). Any suggestions for low cost injection mixing controllers for these three new loops? I love the Tekmar's, but they are not inexpensive....and the Garn has broken the bank. I also need to wire up the Garn (which will be plumbed as a secondary loop through a HX feeding the primary loop). I'd like to use an aquastat in the Garn such that if the temp is below say 130 then the call for heat fires the oil boiler, otherwise if it is over 130, I'd like to turn on the Garn pumps (G1 and G2 in the drawing) to bring heat into the primary. This should give me transparaent operation. I'd also like to be able to run the Garn pumps on demand, i.e. say with a switch, so that I can also set the switch to "forced manual" position and hook the pumps up to timers for freeze protection, should i ever go away during the winter. My plan would be to fire up the Garn, but heat with oil, and use the heat in the garn to keep everything above freezing for the week. A couple of drawings are attached. All sorts of flanges, ball valves, etc. are omitted....just trying to figure out the control system at this point. In an old thread I think I read about an L6006C aquastat switch, which seems like it will send my call for heat to either the oil boiler or the Garn pumps... Do I need to hook up the Garn pumps as a mixing controller, or can I just turn on the pumps at full tilt and allow the current Tekmar 363 to shut down the call for heat when the primary loop is warm? One last question: Can multiple heat demand outputs from multiple controllers (362 and the three new mixing controllers) be wired to the 363 to send out the actual call for heat to the boilers? Or do I need some kind of switching relays? Seems like these things are all 24V AC signals and the phasing of the various demands might cause troubles. Thanks!