Hooking Up A Thermostat How Do I Hook Up A Thermostat To Just Turn On The Blower On My Furnace.?

How do i hook up a thermostat to just turn on the blower on my furnace.? - hooking up a thermostat

Low-voltage system. I have a supplementary hot water through a coil in the furnace. I want to kick the fan in touch when you get heat, and let the main thermostat is connected as a backup for emergencies. Thanks