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Thread: Is there a way to use two thermostats?

  1. #1
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    Is there a way to use two thermostats?

    I have moved into a new-to-me shop. Its basically a two car garage but, it also has a room behind it (with a bar, bed, bathroom, etc, same building under roof), but totally separate, that is heated and cooled with 1.5 ton unit. My shop or the garage part is very well insulated, 2x6 construction and insulated garage doors. I want to tap into the existing hvac system next door, its doable from a ducting point of view and access. What has me scratching my head is how do I deal with the existing thermostat in the other room? The other room is out around the corner with separate door access. The hvac system is obviously going to want to react to the temp in the other room. I won't have any doors or access of any kind between the two. All flex duct will be through the attic. Anybody have any ideas on how I can control heat/cool in shop when other room is not in use (which will be 95% of the time)? Any way to coexist with two separate thermostats and one unit? Randy
    Randy Cox
    Lt Colonel, USAF (ret.)

  2. #2
    Join Date
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    Lake Gaston, Henrico, NC
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    A google search for "zoned heating system" came up with anything you want to know. This is just one example:

    https://swanheating.com/understandin...-systems-work/

  3. #3
    You will also need a return air back to the air handler of the HVAC.

  4. #4
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    It's doable with dampers in the ducting, but it has to be designed correctly. You want to maintain total air flow through the equipment within the proper design range. If you don't, you can have problems like frozen coils or short cycling the AC or furnace. You need a good HVAC person.
    --Certainty is the refuge of a small mind--

  5. #5
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    The super low tech way to do it is to balance the airflow at the vents manually to get a balance that you like, target being even heat/cool throughout. Leaving doors open helps this. It's what I do in my shop, defiantly not perfect, but I didn't want to modify the HVAC.

  6. #6
    Join Date
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    Fairfield County, CT
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    If you really just want two thermostats (without worrying about balancing airflow or anything) ecobee has remote thermostat/occupancy sensors - https://www.ecobee.com/en-us/accesso...upancy-sensor/ where I think you can tell the t-stat when to use which sensor.

  7. #7
    Join Date
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    Quote Originally Posted by Josh Molaver View Post
    If you really just want two thermostats (without worrying about balancing airflow or anything) ecobee has remote thermostat/occupancy sensors - https://www.ecobee.com/en-us/accesso...upancy-sensor/ where I think you can tell the t-stat when to use which sensor.
    Nest thermostats have remote sensors available too. Nice user interface also. I use them in several locations around the house.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  8. #8
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    Are you wanting an easy way to switch which thermostat is used?

    If so, then yes this could be done with a 6 PDT switch. There may be some other HVAC solutions out there but I'm not up on all the details of residential thermostat interfaces.

    One solution would be to connect the 2 thermostats with a 6 pole double throw switch. You would just switch to the thermostat you are wanting to use.

    6PDT Toggle Switch.jpg
    Last edited by Eric Arnsdorff; 07-28-2021 at 10:22 AM.

  9. #9
    Join Date
    Mar 2016
    Location
    Millstone, NJ
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    Is the other space a full time occupancy?
    If it is not and you are looking for occasional use or if the garage wont be used daily the cheep fix is to wire both stats to the unit and leave the one you are not using "off"then run your duct to the new space teeing into the existing ductwork. you will need 2 manual dampers one on existing and one on apartment.

    If it is the better solution would be to have 2 motorized dampers that are wired to the stats. If one calls it opens the NC damper and runs the unit. If 2 call both NC dampers open and the unit runs. This way is better and will allow you to have the shop at 60 and apartment at 70 in the winter.

  10. #10
    Join Date
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    There are at least 3 companies now making dampers / zoned systems that are just the vents, with motorized louvers, thermostats, pressure sensors, etc... They are called smart vents.

    I've been looking into them, as I could use some of the advantages of a zoned system in my present house, but the cost of replacing the dampers in my last house (10 zoned dampers, used to last 10 years, now the crap only lasts about 2 years at $1500 a pop) has turned me off of that scenario.

    One problem with the zoned grills, is that they are only made in a few sizes. And not the ones I need. But this could work for you and be an easy solution.

    Flair is one of them:
    https://flair.co/

    Also Keen:
    https://keenhome.io/

    and Ecovent:
    https://www.ecoventsystems.com/

    They each have their plusses and minuses. But should be an easy self install and cost a lot less than a zoning damper system.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
    - Outside of a dog, a book is man's best friend. Inside of a dog, it's too dark to read.

  11. #11
    Join Date
    Apr 2013
    Location
    Okotoks AB
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    2,907
    I have a Honeywell thermostat that has a portable remote sensor. The thermostat uses whichever sensor you choose. Temps can be adjusted from the thermostat, remote sensor, or mobile device app.

  12. #12
    Join Date
    Mar 2016
    Location
    Exeter, CA
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    I thank you all for the info. Looks like the two thermostats is doable. However, now that I have really looked at my situation and the ducting issues with louvers to change air direction to from the shop, it starts getting complicated and more expensive. I'm becoming more and more tempted to install a mini split and be done with it. Randy
    Last edited by Randall J Cox; 07-29-2021 at 6:00 PM. Reason: clarity
    Randy Cox
    Lt Colonel, USAF (ret.)

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