I purchased a 24,000 BTU forced hot-water heater to be installed in my attached garage, but I'm having a tough time understanding how to wire the fan properly to a thermostat. Currently, I have a 5-zone plus priority 24 volt Argo AZ-6P (120 VAC) Zone Valve controller opperating 3 zones of my home (plus one priority zone for the hot water tank). I would like to have the garage heater opperating on Zone Valve #4. Here is what I think I need to do. Starting with the Top Row wire configuration from Zone Controller Going to the Thermostat: 24 volt Red Wire from Zone Valve Controller to R terminal on Thermostat. White wire from Zone Valve Controller to W Terminal on Thermostat. I think I'm OK there. Now, Bottom Row wire configuration going from Zone Controller to Zone Valve #4. Red wire (24 volt) going from Zone controller to Terminal 1 (top screw) on Zone Valve. White Wire going from Zone controller to Terminal 2 (middle screw) on Zone Valve. Blue Wire going from Zone controller to Terminal 3 (bottom screw) on Zone Valve. I think I'm OK there. Here's where things get tricky for me. The heater fan itself does NOT have any type of relay. It just has your typical 115 volt 3-wire hook-up (hot, neutral, and ground). I'm assuming I need some type of 24 volt relay controlling the power supply to the fan which is triggered by the thermostat. Any recommendations? Also, how do I wire the relay to the thermostat. I'm guessing the green wire goes from the G terminal on the thermostat to one side of the fan relay, but how do I complete the circuit on the relay so that when the zone valve opens the heater fan is triggered. Any help or suggestions would be greatly appreciated! Thank you. Rich A

I am having trouble making sense of all this. Why do you have a fan with a hot water system? The G terminal on a thermostat usually is to run fan only on a forced air system.

The only hot water system I have worked with has a red, green, and white cable running from each thermostat to each zone valve. The zone valve then has another 3 wire cable running back to the boiler so any one thermostat can fire the boiler. Find the transformer the red wire to the thermostat comes off. If you wire the white wire from the thermostat and the other wire from the transformer to the coil of a relay, it should close and turn on the fan when the thermostat calls for heat.

Thanks Labman! I'm sorry, I probably didn't do a very good job describing the heater/fan combo. My home heating system opperates on forced hot water with baseboard heaters. I wanted to use the same "set-up" to heat my garage, so I purchased a forced hot-water hydronic heater. The forced hot water heater I purchased for my garage is a heat exchanger (3/8" serpentine copper tubbing ) with a fan attached to the back of the unit forcing air through the exchanger which in turn heats the air in the garage.

My thermostats don't connect directly to my zone valves. The thermostats run to a zone control box which opperates each zone valve independently as the zones call for heat. My first thought was to use the same 24 volts which supplies power to the number 4 zone (garage zone) to also trigger the fan relay, but I wasn't sure I could "double tap" the wires on top of the zone valve. In other words, can I use the 24 volt wires that will be triggering the number 4 zone valve to open to also trigger the fan relay? I wasn't sure if I could tap off those wires on the zone valve without causing "power robbing" problems to the zone valve or the zone valve control panel. Not sure if I'm making any sense??

How do the zone valves operate? Do they have a motor that comes on, opens the valve, then stops? If so, likely the transformer supplying the current could easily provide the power for a fan relay. You would need a meter to sort out the 2 wires that open the valve.

Do you have an installation manual for the system? It may help sort things out.