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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

Customer Question

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?

Submitted: 4 years ago.
Category: HVAC
Expert:  Mark Henley replied 4 years ago.

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 4 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).
Expert:  Mark Henley replied 4 years ago.

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 4 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.
Expert:  Mark Henley replied 4 years ago.

Hi,

 

It should, is the door switch pressed in ?

 

Thanks

 

Mark

Customer: replied 4 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?
Expert:  Mark Henley replied 4 years ago.

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, Journeyman Technician
Category: HVAC
Satisfied Customers: 3217
Experience: UA Journeyman Pipefitter , HVAC, Refrigeration, DDC controls. 26 years.Commercial & residential
Mark Henley and 2 other HVAC Specialists are ready to help you
Customer: replied 4 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).
Expert:  Mark Henley replied 4 years ago.

Hi Garth,

 

No problem,

 

Thanks

 

Mark

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