Line Voltage Thermostat
Intro
Winter is coming
We need smart thermostats
I was at my friend’s house and we started talking about smart home devices. I told him about the Nest Thermostats at my house and he was really interested in getting some for his apartment. We checked the electric baseboard heaters and existing thermostats in his apartment and realized they all used 208V. The thermostats were basically connected in series to the heaters, which means a lot of current flows through them. This is unlike most of the smart thermostats that use low voltage, usually 12-24V and just flip the power on or off for the devices. This needed a little more searching for the right thermostats.
Mysa Thermostats
Our requirements for thermostats were pretty straight forward. We needed thermostats that could operate at 208V, connect to WiFi, could be controlled by an app, had some scheduling features and matched the white walls. The thermostats were not going to be manually operated, so the display, design, buttons, UI, etc, were less of a priority.
Mysa sells line voltage thermostats for several setups including electric baseboard heaters. The Mysa Smart Thermostat Lite met all the requirements and was relatively inexpensive with the Mysa discounts and Hydro rebates applied. Mysa also provides an app to manage the smart features. The thermostats are built on Tuya IOT platform, so it’s also possible to use Tuya or Smart Life apps and integrations with Alexa and Google Home work seamlessly.
Installation
[!CAUTION]
Most places do not allow you to do electric work without proper certifications. Get a certified electrician to do any wiring work
Old thermostats
We turned off the breakers in the main circuit breaker panel, opened the gang box and took some pictures of the old wiring setup for reference and incase we needed to revert to the old thermostats. The old thermostats were hooked up like
The red and blue wires are supply different power phases. Voltage difference of each one to the neutral is 120V (AC) and the voltage difference between both of them is 208V (AC). The thermostat acts just connects or disconnects the blue wire to the heaters for turning them on or off. The current still flows through the thermostat.
New thermostats
The new thermostats have electronics that need to be powered, unlike the old, mechanical thermostats without any electronics. The new thermostats are able to run on voltages between 120V-240V. We will hook them up to 208V which will be the same as the voltage going into the baseboard heaters. The wiring is not a lot different compared to the old ones, with one exception. We will also connect the red wire to the thermostat so it can get the 208V.
It’s easy to find which wire goes where in the thermostat. The wires on the thermostats are clearly labelled. Connect the first phase wire (blue) to L1, connect the second phase wire (red) to L2(N) and connect the heaters (white with black tape) to Load. The thermostat powers itself using L1 and L2.
Conclusion
The wiring took about 10 minutes. We installed two more thermostats in other rooms too and didn’t run into any issues. The thermostats were up and running as soon as the breakers were flipped back to on position. Pairing the thermostats with WiFi was also seamless using the Mysa app and they installed the latest update. The integration with Alexa worked well.
Thank you for reading. I will post more content shortly.