I plan to install a booster fan in the air duct of my house. I want to wire it to the blower in the air box so it will only come on when the main blower is running. How do I wire it?

Since you may have multiple speeds on your blower in the furnace I might suggest a sail switch. What this does is when there is air flow in the duct it pushes a sail and closes a switch which completes the electrical circuit and brings on the booster fan. This switch can be purchased from an air conditioning supply house and the wiring is simple, just connect the switch to a constant power source, break the circuit with the switch and then connect to the booster fan. Good luck. Mike

I had that question answered pretty well (using a sail switch). Check here https://www.askmehelpdesk.com/electr...tml?eid=281656