furnace transformer capacity and conrolling humidifier from furnace - Canadian TV, Computing and Home Theatre Forums

38racing · 2011-03-21, 02:32 PM

Just as I started to post I think I concluded that I know part of the answer. My question was going to be whether the furnace transformer would have enough power to close a relay for controlling a humidifier. I conclude the answer is yes because it has the power to close the relay in the A/C unit and A/C and humidifier run in different seasons, never together. Update: Duh brain fade. That's no answer as A/C and heat don't run together either. Plan is to have the relay activated when the thermostat calls for heat. In a single stage thermostat that's done by just using the W- terminal to activate the relay. In a 2-stage with w1 and w2 , is the second stage activated by power to w2 only or both w1 and w2. My daughter has a fully modulating Rheem with a Rheem thermostat ( which we assumed was the one that went with the fully modulation feature) so I'm wondering if we will have problems getting power to a relay so that relay is activated when furnace is running on any stage and/or all stages.
It's a Wait 6000 that has a jumper available to use with a switch to bypass the auto heat rise sensor. (which isn't working right for us). This is for the water solenoid , not the humidistat part.

txv · 2011-03-21, 05:00 PM

The circuit board should have humidifier terminals. If they're 24 volts, you can connect the humidistat directly up to the board; if they're 120 volts, use a stepdown transformer.

If there are no terminals, you can wire the humidifier to W1 and C.

Two stage thermostats keep W1 energized when there's a call for second stage heat on W2.

Rheem's modulating thermostat doesn't use W2 as far as I know - W1 is used to turn the furnace on and another wire is used to control output.

In cooling mode the transformer is used to power a heavy contactor and blower relay, so I don't think you'll have a problem.

38racing · 2011-03-26, 11:55 PM

You were right. Turns out there is a built in humidifier relay that closes contacts when furnace is heat on and blower on, so we used that to control the heat sensor on/off part of the humidifier. Since the thermostat has humidifier function (closes R to HM on call for both heat and humidity) we connected the HM to a relay (had a spare wire running from furnace to stat) and used a relay to open and close the built-in humidistat circuit of the humiidfier (setting built-in to max humidity). Noted that it had a V terminal on stat and furnace. Looks like they had to add the wire for that and they ran a pair and that's where we got the spare wire for the HM.

2011-03-21, 02:32 PM	#1
38racing Join Date: Jun 2010 Posts: 213	furnace transformer capacity and conrolling humidifier from furnace Just as I started to post I think I concluded that I know part of the answer. My question was going to be whether the furnace transformer would have enough power to close a relay for controlling a humidifier. I conclude the answer is yes because it has the power to close the relay in the A/C unit and A/C and humidifier run in different seasons, never together. Update: Duh brain fade. That's no answer as A/C and heat don't run together either. Plan is to have the relay activated when the thermostat calls for heat. In a single stage thermostat that's done by just using the W- terminal to activate the relay. In a 2-stage with w1 and w2 , is the second stage activated by power to w2 only or both w1 and w2. My daughter has a fully modulating Rheem with a Rheem thermostat ( which we assumed was the one that went with the fully modulation feature) so I'm wondering if we will have problems getting power to a relay so that relay is activated when furnace is running on any stage and/or all stages. It's a Wait 6000 that has a jumper available to use with a switch to bypass the auto heat rise sensor. (which isn't working right for us). This is for the water solenoid , not the humidistat part.

2011-03-21, 05:00 PM	#2
txv Veteran Join Date: Oct 2008 Location: Canada Posts: 1,740	The circuit board should have humidifier terminals. If they're 24 volts, you can connect the humidistat directly up to the board; if they're 120 volts, use a stepdown transformer. If there are no terminals, you can wire the humidifier to W1 and C. Two stage thermostats keep W1 energized when there's a call for second stage heat on W2. Rheem's modulating thermostat doesn't use W2 as far as I know - W1 is used to turn the furnace on and another wire is used to control output. In cooling mode the transformer is used to power a heavy contactor and blower relay, so I don't think you'll have a problem. __________________ WARNING: The HVAC information I provide is not based on field experience and DOES NOT constitute professional advice.

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2011-03-26, 11:55 PM	#3
38racing Join Date: Jun 2010 Posts: 213	You were right. Turns out there is a built in humidifier relay that closes contacts when furnace is heat on and blower on, so we used that to control the heat sensor on/off part of the humidifier. Since the thermostat has humidifier function (closes R to HM on call for both heat and humidity) we connected the HM to a relay (had a spare wire running from furnace to stat) and used a relay to open and close the built-in humidistat circuit of the humiidfier (setting built-in to max humidity). Noted that it had a V terminal on stat and furnace. Looks like they had to add the wire for that and they ran a pair and that's where we got the spare wire for the HM.