"HUM" terminal for humidifier control?

[b***@gmail.com]

Hi! Question for those who know. Is there a benefit of using an external 24VAC source to power the humidifier like - EAC/HUM output on the furnace board vs taking it from the T-STAT. My ecobee3 can be wired and configured to do both.

1st scenario(2-wire ACC+/ACC-) ecobee3 will short two terminals internally to complete the loop for the secondary(24VAC) to activate the humidifier.

2nd scenario(1-wire ACC+) ecobee3 will send its own 24VAC to activate humidifier.

Any thoughts?

Thank you.

[s***@gmail.com]

Post by b***@gmail.com
Hi! Question for those who know. Is there a benefit of using an external 24VAC source to power the humidifier like - EAC/HUM output on the furnace board vs taking it from the T-STAT. My ecobee3 can be wired and configured to do both.
1st scenario(2-wire ACC+/ACC-) ecobee3 will short two terminals internally to complete the loop for the secondary(24VAC) to activate the humidifier.
2nd scenario(1-wire ACC+) ecobee3 will send its own 24VAC to activate humidifier.
Any thoughts?
Thank you.

EAC is usually 120vac turned on with blower.
HUM is usually 120vac turned on with heat. Sometimes there is a separate 24vac hum. Needs humidistat.

1st scenario - needed for humidifier needing dry contacts that have own transformer. Steam types.
2nd scenario - good for bypass humidifiers that just open valve so don't have to install transformer.

Rare case that furnace transformer is overloaded and doesn't have enough power to trigger valve. Then use scenario 1 with external transformer.

[z***@comcast.net]

Post by b***@gmail.com
Hi! Question for those who know. Is there a benefit of using an external 24VAC source to power the humidifier like - EAC/HUM output on the furnace board vs taking it from the T-STAT. My ecobee3 can be wired and configured to do both.
1st scenario(2-wire ACC+/ACC-) ecobee3 will short two terminals internally to complete the loop for the secondary(24VAC) to activate the humidifier.
2nd scenario(1-wire ACC+) ecobee3 will send its own 24VAC to activate humidifier.
Any thoughts?
Thank you.

My new Carrier OBL furnace HUM terminal is 115VAC. Some seem to be 24VAC. I have been searching for the current rating, I suspect .5AMPS for my 115V HUM is correct but have not been able to confirm. Yours may vary based on your model unit.