I have oil fired baseboard heating and a separate AC system. Currently I have two older thermostats installed. I'd like to replace with a single unit, however I can't locate any thermostat that allows me to disable the fan which I need to do if I'm heating the house.

All the thermostats I can find only allow for either the fan being in AUTO or ON.

Any suggestions?

  • Set it to auto, it can not turn on a fan that is not on the heating system and will turn on the AC fan when it calls for AC.
    – Alaska Man
    Apr 4 at 19:20
  • the AC system has a fan....all the thermostats seem to only have one fan connection so if I connect the ac fan, the thermostat also turns on the fan when the heating system is active.
    – bob wolff
    Apr 4 at 19:24
  • Are you saying that when the thermostat calls for heat it is turning on the AC fan? In auto mode, When wired properly, If it calls for the heat it should not be turning any AC on. Perhaps this will help - diy.stackexchange.com/questions/37276/…
    – Alaska Man
    Apr 4 at 20:15
  • ok...the thermostat turns the fan on when calling for heat or calling for ac.....how does it know my heating system doesn't have a fan? It works the same if you have a single air handler for both the heat and ac.....There is only ONE fan relay in the thermostat....if I could find a thermostat that had two fan relays (one for heat an done for cool) that would work...there doesn't seem to be any thermostats like that. And I can't find any thermostat that allows me to setup a heating system that doesn't have a fan but a cooling system that does. Is that a bit clearer?
    – bob wolff
    Apr 4 at 22:15
  • @bobwolff See answers below. There is a simple solution that 3phaseEd and I offered. No "one off" solution needed, just have to get into the installer setup and configure it for your situation. Apr 4 at 22:57

Simply set your thermostat to "fossil" or "gas/oil" mode

Most thermostats out there support what you describe, as it turns out, as gas furnaces control their blower automatically by default, and only use the G terminal as an override to turn the blower on when the system is otherwise not running. So, simply set your thermostat of choice to "fossil" or "gas/oil", and you'll be set.

(If you're having trouble finding the option, check the installer's manual for your thermostat. Older electronic 'stats had a small switch inside that set this, while newer ones have a software option instead.)

  • Dang dude, I said the same thing about an hour before you did! and you got the UV! LOL. I'll give you an UV as well, since we agree on the answer, even if I think my answer is more specific and detailed. Give me an UV as well....moma needs a new pair of shoes. Happy Easter. Apr 4 at 22:54

I wish I could post this as a comment rather than an answer, but pictures aren't supported in comments, but here goes. This isn't a product recommendation, just an example of what might work for you. Most sophisticated thermostats have a LOT of settings for various types of heating/cooling configurations. I have in-floor hydronic heating and A/C on the same t-stat and it works fine, the only time the t-stat turns on the air handler is when the in-floor system can't achieve setpoint within a certain amount of time. The air handler has a hydronic fan coil to supplement the in-floor radiant.

Lots of the settings are not obvious when you're just looking at consumer brochures...you have to get into the installer setup manuals to truly see what's possible. It looks like setting 180 on the Honeywell VisionPro8000 would work for you. Set it to 0 and the equipment controls the fan.

Don't take this to the bank, I'm just a decent DIYer and try to help. Maybe Ed Beal (HVAC expert) will weigh in and comment. But it looks like a potential option. Here is a link to the installation manual for your further edification: https://www.dhontario.com/catalog/accessories/controls/honeywell-visionpro-8000-universal-programmable-thermostat/

part of installer setup instructions for Tstat

  • yes, it looks like that one (or one with similar settings) would do the trick...many thanks.....surprising I couldn't locate one at any of the local stores or online....again thanks to everyone for the help. Stay Safe!!! Enjoy the nice weather!!!
    – bob wolff
    Apr 6 at 2:46

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