Wifi Control of a Millivolt Thermostat

Gbridgem
Gbridgem Registered Users Posts: 13
We have an off grid cabin in Alberta that is heated in the winter with a propane stove - controlled by a 2 wire a millivolt thermostat. Our solar set up provides lots of power in the summer but not enough to be bullet-proof reliable in the winter The stove is not impacted by a loss of power when we are not there. We recently added internet for when we do have power. It would be nice if we could control the thermostat via wifi when we do have power. However, all models seem to be powered via a 24v power supply- unlike the current 750 millivolt thermostat (that has batteries for the display). I am concerned that if I go to the 24v wifi thermostat, the heat would not come on if we lost power as a result of low voltage. I would appreciate any advice you might have. Perhaps I could connect the 24v "c wire" directly to my 24VDC battery bank and in that way still have enough power in the event that my inverter trips off. Guy

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Here is a long thread from Hearth:

    http://www.hearth.com/talk/threads/installing-24-volt-wifi-thermostat-on-millivolt-stoves.114018/

    I have not read through it--But it looks to discuss the issue from many sides.

    More or less, you can put a 24 volt relay that simply closes the relay to turn on the heater, or open the relay to turn off the heater (simply connect the two millivolt leads to the relay contacts).

    If you are concerned with "computer what ifs"... Get two mechanical thermostats (or one of them, at least, battery powered wall room thermostat).

    First in parallel with the relay. Set the regular millivolt thermostat to 55F (or whatever you want as low temp)--This will help reduce the threat of freezing pipes.ran

    You can set up a second mechanical thermostat that "opens" when the temperature rises... Put this in series with the relay leads (turns off when temperature is >60-70 degrees) which stops thea wifi controller crash from leaving the furnance on--Or put in series with the line direct to the finance (stops any stuck contact command to the furnace).

    I am a little surprised that NEST does not control millivolt gas furnace... You would still need some sort of power to the controller (24 volts, batteries, etc.) to power the brains.

    [h=2]Heating and cooling systems that are incompatible with the Nest Learning Thermostat[/h] The Nest Learning Thermostat is not compatible with line voltage, millivolt systems or low voltage systems with incompatible wires. The Nest Thermostat is not compatible with some systems without a common wire installed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    A simple trick that wastes a small amount of power is to place a resistor in close proximity with the thermostat bi-metal. If you apply power to the resistor it will heat up the thermostat, causing it to turn off the stove or furnace.
    If power to the control is lost it will fail in the direction of letting the thermostat operate normally.
    It may not be able to conclusively shut the heater off if it gets really cold inside, but it would allow you to change the set point of the thermostat by a predictable amount.
    SMA SB 3000, old BP panels.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    Do you have a landline/wired telephone? There is an excellent product that I have been using with a few of my clients above 10,000 feet.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net