I am installing a Honeywell HE360B Powered Humidifier on a Bryant Plus 90 furnace, Model 350AAV. The furnace has a HUM terminal supplying 24VAC. I want the humidifier to run on the heat cycle, but I am not sure about using that 24VAC terminal, I am thinking the humidifier is already supplying 24VAC for the humidistat circuit. I was trying to avoid using a current relay sensor or a sail switch.

Current relays work well and a sail switch takes a little more work to install works well also. Try not to reinvent the wheel since it has already been done. The humid terminal can only supply so much power so unless you use it to activate a separate relay you might be asking for trouble to start with.