We had a water heater installed a few years ago, that along with a heat exchanger heats the house, so it comes with a thermostat. Salesman tells me in glowing terms about the WiFi-enabled thermostat they're "giving" me, to which I reply "ABSOLUTELY NOT"... turns out they have an old-style one that's $300 cheaper, and... has worked fine for the entire time, without poking a severe security hole in my WiFi network.