My current setup is as follows. I've got a 2-story home with a full basement totaling 3,600sq ft. I have a 100k BTU air handler in the basement that supplies forced air heat to the basement and first floor. I have another 100k BTU air handler in the attic of the house that will supply the second floor of the house with forced air heat. It is currently not hooked up. I've had a Central Boiler 6048 installed for a year now. It holds 400 gallons of water. I currently have a Taco 009 pump supplying a series circuit containing a domestic hot water HX followed by the basement air handler. I bypass the basement air handler in the summer months to heat my hot water but that's not important. I'm looking at installing the attic air handler but do not want to plumb it in series with everything else. I have a 5* temperature drop between the OWB and the 155* thermostat housing. That figure is taken from the digital readout on my OWB minus a readout from a digital thermometer I have installed at the inlet of the thermostat housing. I have 75' of ThermoPex buried 18" down to supply the house. Those are the only temperatures I have measured at this time. At this time I have hot water flowing through my house 24/7 and I feel that I am wasting wood. I realize that any heat lost in the house is actually heating the house but I want to heat my house with forced air heat, not radiant heat. That's a different discussion entirely though. I want to limit water flow to the house by installing an electronic 3-way valve at the OWB outlet that will direct water back into the OWB when I am not calling for heat. This will bypass the 75' run of ThermoPex and I believe will reduce the amount of wood I will burn. I will be installing a temp controller on my hot water tank that will signal when it needs heated up again and each of the air handlers will have separate thermostats. Each signal will be interlocked so that only one zone can call for water at a time. I'll be using electronic ball valves for the zone valves. The Taco 009 pump is a high head pump and coupled with the interlocks and check valves I'm wanting to use I believe I will only need that one pump for this system. I have attached a few crude layouts of my current system and the system I'm looking at doing. I'd appreciate any criticism of my idea as to why it will or will not work, thank you!