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Mark Henley
Mark Henley, Journeyman Technician
Category: HVAC
Satisfied Customers: 3217
Experience:  UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
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I want to wire my furnace humidifier to my furnace so that

This answer was rated:

I want to wire my furnace humidifier to my furnace so that when the humidifier goes on, the blower on the gas furnace will start to. My furnace has a terminal marked "HUM" for humidifier. Is that what I should use?

The furnace control pannel has the following 24 VAC terminals.

G (fan); B (24 V com); W (heat); Y (AC); R (24 VAC); There is also a separte 24 VAC "HUM" terminal.

I'm thinking I could connect my humidifier to the B and HUM terminals, but how could it also turn the blower on?

Hi,

 

You would have to have an isolation relay installed that will energize the G terminal on the furnace when the humidistat calls for humidification. The G terminal had to be powered by the R terminal power on the furnace, you can't just run 24 volts to it from a separate transformer that's why you will need a relay. Let me know if you need help with that.

 

Thanks

 

Mark

Customer: replied 7 years ago.
Would it work if I ran the power for the humidifier from the R terminal to the humidistat and then had two wires from the humidistat, one to the humidifier and one to the G terminal?

(Or maybe I should take the power from the HUM terminal instead of the R terminal).

Hi,

 

You don't want to run the humidifier solenoid off of the furnace R terminal, the HUM terminals don't do what you need them to.

 

Thanks

 

Mark

Customer: replied 7 years ago.
I understand that the power for the G terminal needs to come from the same transformer that is on the furnace. But if I pura jumper wire between the R terminal and the G terminal nothing happens, the fan does not start. That confuses me.

Hi,

 

It should, is the door switch pressed in ?

 

Thanks

 

Mark

Customer: replied 7 years ago.
No, I had the cover off.

The HUM terminal says that it is a 24 VAC terminal for a humidifier with a limit of 500 mA. Shouldn't this work for the power supply to my humidifier?

Hi,

 

It will only come on when the heat is on, you wanted to signal the unit to come on when the humidifier called, it won;t work that way.

 

Thanks

 

Mark

Mark Henley and other HVAC Specialists are ready to help you
Customer: replied 7 years ago.
Oh thank you Mark. Now I understand what the HUM terminal does! Now I understand the need for the relay. You have answered my question. Thanks. (Sorry it took so many follow ups).

Hi Garth,

 

No problem,

 

Thanks

 

Mark