Nest, Aprilaire, Overthinking

Old 03-27-21, 07:15 AM
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Nest, Aprilaire, Overthinking

I am an electrician by trade and we've had more and more customers asking for us to install smart thermostats when we are making house calls. We have a customer that wants us to install a Nest thermostat as part of a home update and they want to combine their humidistat and thermostat controls into the Nest. I can reroute the humidifier wiring to the Nest and furnace board but the humidifier is currently being powered by a separate transformer, which is where the overthinking comes in. Does the furnace board have the capacity to run the solenoid with being overloaded on the RH and C terminals, or is the extra transformer necessary to prevent damaging the board?

I'm working with:
Humidifier: Aprilaire Model 550, listed 24v, .5 amp.
The solenoid is 24v, 2.3 watt (less than .1 amp, and the only thing actually being powered on the Aprilaire)
Furnace: Trane XL 80

Any insight would be greatly appreciated.
Old 03-27-21, 07:39 AM
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Welcome to the forums.

Most furnace transformers can supply 40va of power. Your Trane XL80 can.
Most thermostats are designed to switch a maximum of 1A.

You won't have any problem running that humidifier off the furnace transformer.
JCMadison voted this post useful.
Old 03-31-21, 07:06 AM
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Hi, are you using the digital controller or manual?
Geo 🇺🇸

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