Omnistat2 Thermostat Pre-Wire

I just encountered the same situation. My Robertshaw 9851i thermostat would activate the humidifier only if the fan was active whereas my new HAI Omnistat2 RC2000 will activate the Humidifier even if the Fan is inactive. It's a Desert Spring humidifer and it needs air flow in order to evaporate the water on its discs so I need to alter the Omnistat's operation.

I'd like the Humidifer to be activated only if the RC2000's "H" (Humidifier) AND "G" (Fan) terminals are enabled. I believe I need a relay that is powered by the "G" (Fan) line. When activated by the Fan line, the relay closes its contacts and allows for the Humidifier to be activated but only if the RC2000 activates its "H" (Humidifer) line. Does this make sense? Anyone see why it would not work?

Is there not a way to program the Omnistat2 to enable the fan when it has a call for humidity? I am looking into buying an Omnistat2 as well, but I was hoping that it could be controlled a lot more carefully than that, rather than needing to add your own relays. Otherwise, by wiring a relay as you suggest, you will only get the humidifer running if you have a call for heat.

Thanks,

Eric
 
The RC-2000 has a setting to control the fan's operation during a call for heat. By default, it does not call the fan when it activates heat. The assumption is that the furnace will activate its own fan when heat is called (that's how my furnace works). However, you can have the thermostat call the fan when it calls for heat.

There is no similar setting for humidity. You cannot have it automatically call the fan whenever it makes a call for humidity.

If the RC-2000 is connected to a controller or HA software, you could have it detect the humidity call and then, via a controller rule, force the thermostat to activate the fan.

In my case, I want the RC-2000 to be capable of operating autonomously. By adding a relay, the goal is to operate the humidifier only if the humidity and fan lines are active.

I agree that it'd be best if the thermostat was able to handle this situation without the need for a relay. My Robertshaw 9851i did all of this and more (adjust the humidity setpoint based on the exterior temperature) ... but it was not a communicating thermostat.
 
In my case, I want the RC-2000 to be capable of operating autonomously. By adding a relay, the goal is to operate the humidifier only if the humidity and fan lines are active.

123 When I look at what you are doing to solve this problem. It seems like the logic should be that the Fan comes on when the Humidity is triggered. The Humidity being the trigger here.

I believe in my situation I want to set the Humidity Set Point. If the RC2000 determines that the Humidifier needs to run it will trigger. I want it to then to turn on the Humidifier and also reach out through a relay to turn on the fan.

When the humidity hits the set point, the the RC2000 will turn off the Humidifier which though a relay will turn off the fan.

In my logic above, will your diagram work for me? If so, will the relay you referenced also work?

CHRISDUTCHYN provided a diagram on a post June25th (HAI RC2000). I cannot find an MY5N Relay in any of my searches.

Thank you for your input.
 
123 When I look at what you are doing to solve this problem. It seems like the logic should be that the Fan comes on when the Humidity is triggered. The Humidity being the trigger here.

I believe in my situation I want to set the Humidity Set Point. If the RC2000 determines that the Humidifier needs to run it will trigger. I want it to then to turn on the Humidifier and also reach out through a relay to turn on the fan.

When the humidity hits the set point, the the RC2000 will turn off the Humidifier which though a relay will turn off the fan.

In my logic above, will your diagram work for me? If so, will the relay you referenced also work?

GotHAI,

No, the above diagram won't work for your case. I agree entirely with your logic, however. As far as I see it, the humidity control should be the trigger. However, hot air holds humidity better than cold air, so I can understand 123's desire to only have the humidifier running when the furnace fan is running (indicating that the furnace is producing heat).

I set my own furnace up the way you specify. My control line to the relay solenoid is the H line, and my N/O relay will short between the G and the C lines when it closes. That forces the fan to turn on whenever the humidifier is triggered.

As for what relay you need, you need a 24VAC Normally Open relay. Most electronic shops carry these. If not, your local HVAC supplier should have some.

Good luck,

Eric
 
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