I'm trying to install a new Nest-brand thermometer in my parents' house (unscrewing a thermometer from the wall and screwing on the new one.
The first instruction in the manual is to shut off power to the house. What is the risk of not shutting off the power?
Best Answer
Some systems are line-voltage in which case you could get a 120V or even 240V shock from the thermostat wiring. I believe the Nest is designed for 24V systems. It does seem a bit extreme to suggest turning off the power to your entire house. I would probably settle with turning off the power to your furnace and then verifying with a non-contact voltage tester to ensure none of the wires are live.
On many thermostats, you can verify they are not getting power from the furnace by removing the batteries - if this display stays on, it's getting external power. If the display dies, then its not.
Always assume it's live until proven otherwise!