Duct Fan and Furnace

[emersonvier]

I need to turn on/off my duct fan when the furnace turn on/off, I have Nest Thermostat to control my furnace and a zwave outlet to control duct fan, how can I make this work together?

[napalmcsr]

Do you have one of the best integrations working for you? If so it should be easy to make a rule to control the fan using thermostat operating state

[emersonvier]

Hi I think do you means "Nest Integration", no after google "close" the doors I can not connect my Nest to Hubitat.

[aaiyar]

Can I strongly recommend you control the in-duct blower in a simpler way? Here are two choices. They may sound complicated, but they work very reliably.

1. Wire the in-duct blower to a pressure switch that detects pressure upstream of the blower. When air-pressure is detected, the switch comes on and the blower runs. When there's no pressure, the switch turns off. I use this for an in-duct booster fan that is in my dryer duct.

2. I use this second method for my HVAC ducting. I have a split-coil current transducer (CT) that senses current in the main furnace blower. When CT senses current (i.e. the furnace blower is on), it turns on the in-duct blower via a relay. When there's no current, the in-duct blower turns off.

Both methods have worked super reliably for more than five years now.

Here's an example of an air pressure switch.

I don't have links handy to the CT and relay that I used, but I purchased them from Functional Devices.