How to install a smart thermostat can vary widely depending on your HVAC system. You can hire a professional electrician to handle the installation or to answer any questions before you attempt the installation yourself. That said, all of the smart thermostats I've tested follow a pretty consistent step-by-step process. If you're comfortable with basic electrical work and know whether your system is compatible with the specific model you want to buy, it's a simple DIY process. Check out my article about how to install the Nest Thermostat for a basic overview of the steps, but remember it could vary based on the system you have at home.