Warning- All work with high voltage equipment is very dangerous and can be fatal. This work should be done by a professional electrician. Improper installation may lead to device failure or possibly an electrical fire. Damage to the thermostat due to improper installation is not covered under warranty.
Before you install Mysa, you should Check Compatibility. This will help you determine if Mysa is compatible with your heating system. If you are certain that your gang box only has two wires, Mysa is not compatible with that system. However, just because this one gang box has two wires, it doesn't mean that all the other gang boxes in your house have two wires. Be sure to check all the other gang wires in your home.
Take a look at the picture below, there are only two wires connected to the thermostat. However, there is also another pair of wires, the 2 white ones, which would make for a total of 4 wires coming from this gang box. This scenario is compatible with Mysa.