>>> For instance, I have one rigged up across a zone valve on my mom's "dumb" furnace and it's now smart furnace that heats the house up before she wakes up and

>>> For instance, I have one rigged up across a zone valve on my mom's "dumb" furnace and it's now smart furnace that heats the house up before she wakes up and controls the temperature to whatever tolerance she wants. One thing to keep in mind. Your fire insurance might not cover that.