Why fan signal for Heat/Cool? (One-Dev)

Currently running the dev build (US) and have just some general thoughts and questions. (Thing is rocking btw and you guys are great)

I know all HVACs are different, I was just curious why the fan signal is always turned on with heat/cool. I know most would never notice and it doesn’t really “hurt” to have it on, but if I send voltage down heat(white) or cool(yellow) the fan will automatically turn on with my unit. I imagine this is common with newer HVAC units.

Normally this would be just semantics, but since I have “Gas” heat the following happened with the old thermostat:

  • Gas will kick on
  • HVAC waits for a few seconds.
  • lights gas
  • waits about 10 seconds and then fan(blower) kicks on

Since the fan signal is sent with the heat signal via Hestia… the following happens:

  • Fan and Gas kick on at same time
  • Hvac waits for a few seconds and then automatically shuts fan off over-riding thermostat
  • lights gas
  • waits about 10 seconds and then fan kicks on again

I have already customized the fan control to fit my needs specifically, was just curious if anyone else has ran into this.

I thought there was already a delay added from HestiaPi too to turn fan on. Maybe I am wrong.
From your description I believe there is no need for the fan wire to be connected to HestiaPi as it is handled “automatically” from your system unless you want fan-only use in which case you will need to keep the wire as is on HestiaPi.

IIRC I was asked to put in controls to ensure that the heat could never be on while the fan is not on. I assumed this is for HVAC systems that can’t control their own fan. Not having that wide of an exposure to different HVAC systems I can’t say how common that is, if at all. Anyway, in order to make sure that case could never happen, the fan gets turned on first and then there is a very short delay and then the heater kicks on. Going the other way the heater will turn off first and then the fan.

If this isn’t correct behavior I can definitely change it in the baseline. I just need to know what the correct behavior is.

I was hoping more would chime in and kind of just wanted to open a discussion about it. I would be a particular case (which I am fine with and can customize to fit my needs). I was just seeing if anyone else ran into this in the HVAC mode.

Not knowing how many of these are new systems, here is a map of breakdown of current HVAC in the US. My setup falling into the natural gas category.

I am fairly certain the group that falls into the “Electric” category would never notice if the fan was switched on or not as both get turned on at the same time.

Well, I too am in the HVAC with natural gas category and I do not see the same behavior as you. I think it has more to do with the specific HVAC system than the fact that it’s natural gas.

Ok cool, that is what I was after. Just curious if others had seen the same behavior with the same setup. Thanks

I’m using a gas boiler in the US and the Fan control is useless for me and feel like i should be able to turn it off but cant from the web ui. I found it odd to see the fan on while the boiler wasnt in heat mode, and when this was the case I couldnt see the current set temp in the UI on the touch screen which was kinda odd. Also using the dev build currently.

By turn it off do you mean not show it? You can do so be editing the default.sitemap file and just remove the lines that show the fan. I’d need far more information to diagnose the fan being on while the boiler isn’t heating. I don’t really know anything about the LCD ui.

Blase116 would like some discussion: I’m pretty sure the Green(fan) wire should only be on when the fan is set ON by the user. Fan control during a heating cycle is managed by the furnace and only the white wire need be on. This is the “auto” behavior of most commercial thermostats. Most North American furnaces can be operated with only a 2 wire thermostat (red/white), the green wire is meant to alternatively activate the fan and in some province/state codes, this is required for extra ventilation on demand. I’m testing out the HestiaPi because I want to schedule extra fan time, my Honeywell programmable thermostat doesn’t do this (though more expensive models do).