Is it acceptable to wire a humidifier to my gas furnace using just the W & C wires in the control board?

Question

I'm looking to install a AprilAire 500M humidifier on to my furnace with the main goal that the humidifier switches on only when the heating switches on. I'm not looking to have the humidifier work when the A/C is on or when only the fan is on.

To accomplish this, my thinking here is to wire up the humidifier directly to the accessory terminals on the furnace's control board, specifically to the "W" and to the "C" wires.

Looking at the control wiring diagram, it specifies that the accessory terminals must be 10VA minimum. I just want to make sure I don't cause some sort of overload of the furnace by wiring it this way. Any concerns with this approach? Is this an acceptable way of wiring in the humidifier?

Furnace - Nortek KG7SA 108C-35C1

Answer 1

Yes the humidifier can be powered that way. Really the power demand is on the furnace transformer and on the relay in the thermostat - the furnace control board wouldn't be carrying the power for the humidifier.

You'll still need a humidistat - the humidity will get much too high if you wire it so that the humidifier always runs when the furnace runs. A basic switch type humidistat can be added to the loop: W - humidistat - water valve - C.