Control an external fan

[WayneC]

I think this might be possible but looking for ideas/feedback. I need to control an external fan (external to the furnace). I believe there is a way to do this all from the Nest thermostat but not 100%. Was thinking perhaps wire (with a relay) to the aux heat connection (W2). But I’m not sure what triggers the W2 connection. Can it be set to just automatically trigger when calling for heat from the furnace? 

[Patrick_Caezza]

Do you want independent control of the fan from the systems fan?

[Jenelyn_O]

Hi there,

Thanks for posting in the Google Nest Community forum. Could you please share with us the photo of the wires connected to your control board? Also, as Patrick_Caezza asked, do you want to control your fan from its system independently? 

I appreciate your help, @Patrick_Caezza.

Best,

Jenelyn

[WayneC]

What I’m trying to do is as follows. I have a building that I want to provide heat. I want to use a duct heater, something like this https://www.gordonelectricsupply.com/p/Stel-Pro-Sdhr10080002-8000W-240V-Htr/6265996?srsltid=Ad5pg_H7...

these I know I can control with a nest thermostat. What I need to be able to do is run a little duct work, connect it up with the duct heater. But duct heaters don’t have fans. So I can get an appropriate duct fan, but it needs to run for a period of time after the heat turns off, like a furnace would.  So when the thermostat calls for heat the fan needs to kick on, when up to temp I need the fan to stay on about 30 seconds after the duct heater shuts off. I haven’t bought anything to date. Just trying to come up with an idea on how to make this work. I want to use Nest because I have other Nest thermostats in traditional deployments. This would allow me to use 1 application and control everything remotely. Basically I’m trying to create. Poor man’s furnace for a small out building.

[Patrick_Caezza]

@WayneC 

You should be able to use a relay with a built-in delay to hold it closed for a set period of time.

You would want a 24Vac relay and would wire it to the G terminal.

Something like this.

This circuit is for demonstration purposes only and I offer no guarantee it will work as needed.

[WayneC]

Thank you @Patrick_Caezza . Understand the relay with a delay. So when the Nest thermostat calls for heat, the G wire connection is activated as well, is that correct? If so, what you propose should work just like I’m looking for.

[Patrick_Caezza]

@WayneC 

Based on my understanding of how it works, I would say yes.

[Jenelyn_O]

Hi there,

Thanks for reaching out. I hope you get the answer you're looking for. Please let us know if you still have any questions or concerns, as I'll be willing to assist you from here. 

I appreciate your help, @Patrick_Caezza.

Best,

Jenelyn

[Jenelyn_O]

Hi folks,

I wanted to follow up if you still need help. Please let me know if you’re still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,

Jenelyn

[Markjosephp]

Hello WayneC,

I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours.

Thanks,

Mark