It may sound preposterous, but some people are afraid smart thermostats are bad for heating and air conditioning systems. Here’s the good news: You don’t have much to worry about, but there are some important things to keep in mind.
A relatively recent post on Reddit recounted an HVAC technician’s warning about smart thermostats:
“He said he never recommends them and that their company is REGULARLY replacing systems that have failed or prematurely broken down due to the Nest overworking the computing systems/motherboards built in to most HVAC units—even brand new models.”
The technician isn’t completely full of it. If your smart thermostat isn’t wired up correctly, then it can cause problems for your HVAC system. However, his explanation is mostly filled with a lot of FUD (Fear, Uncertainty, and Doubt.)
It’s All About the C Wire, Baby
Every thermostat has a handful of wires connected to it (either four or five) that lead back to the electrical control board of your HVAC system. Each wire is usually responsible for something specific, like one wire is for cooling, and another wire is for heating. Many systems have a “C wire” (or “common wire”), which is dedicated to providing electricity to the thermostat to power the screen and other electronic functions.
Older systems usually don’t have a C wire, though, because back then thermostats didn’t require electricity thanks to the fully mechanical operation of mercury-switched thermostats. But today, most modern thermostats have more bells and whistles, which require electricity to run. Thus, the purpose of the C wire.
A C wire isn’t necessarily required for smart thermostats, but it’s highly recommended. And if your thermostat’s wiring includes a C wire, you should connect it to your smart thermostat—most problems that arise due to the smart thermostat happen because there’s no C wire connected to it.