Either humidistat or thermostat causes fan to run

Hey Pro’s,


So I have a new system that isn’t humidifying so well. Before I call a professional to take a look, I was hoping to understand what is technically possible with my equipment so I don’t accept any bad advice!




Furnace: G9MVE furnace (Two stage)


Humidifier: Honeywell HE100C, (bypass, installed on the return air duct). The


Thermostat: Nest V2




See attached




Based on this setup, my humidifier only runs when heat is on. The problem here is that the house retains heat very well, so the heat does not come on often enough to maintain a reasonable humidity. I’m in Ontario, Canada so the cold weather saps all the moisture from the air and I’m around 23% RH but I’m looking for ~ 50% RH. Just put down $$$ of new hardwood, so maintaining the right humidity is very important!




When the humidistat recognizes low humidity, it turns on the humidifier + turns on the fan, (even if the furnace is not running). During winter I would set the humidistat, and in summer turn it off and close the bypass damper.


I’ve been reading online and it seems it could be implemented by connecting the EAC (110vac, which runs anytime fan is on) to a transformer (24vac) and connecting the humidifier to that, then bridging the fan on the thermostat to run whenever the humidity on the thermostat is low.


Is this even possible? Could it be solved with some clever wiring/bridging? I’d like to avoid paying for new equipment if it could be solved with what I have!




Attached Images


Either humidistat or thermostat causes fan to run

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