You’ve just decided to make your home heating smarter. Maybe you want a thermostat you can control from your phone, or you’re tired of guessing when to turn the heater off. Then you open the wall plate— and find two thick wires staring back at you. No “C” wire. No “neutral.” Just black and red, or maybe black and white. If that sounds familiar, you’ve met one of the most confusing parts of home heating upgrades: line voltage wiring and relay power supplies . Let’s break it down in plain English. What “Line Voltage” Really Means Most homes in North America use two kinds of thermostat systems , depending on what type of heater they control: Type Voltage Typical Systems Wire Size Example Low Voltage (24 V) 24 volts Central HVAC, heat pumps Thin, multi-colored wires Ecobee, Nest, Honeywell Line Voltage (120–240 V) Household power Electric baseboard, radiant floor Thick wires, usually black/white or black/red Mechanical or smart line-voltage thermostats If your therm...
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