Thermostat wiring guides

• Thermostat Wire Colors Chart (And Why You Shouldn’t Trust It)Typical thermostat wire colors for R, W, Y, G, C and O/B, plus why installers go by terminal letters instead of colors.
• No C Wire? Your Options for Every Smart Thermostat BrandHow to install a Nest, ecobee, Honeywell or Amazon smart thermostat without a C wire: the right adapter for each brand, and when you need new wire.
• Heat Pump Thermostat Wiring: O/B, AUX and E Made SimpleA plain-English guide to heat pump thermostat wiring: reversing valve O vs B, auxiliary heat, emergency heat, and dual fuel, with brand-specific notes.
• Line Voltage vs Low Voltage Thermostats: Check Before You BuyHow to tell a 120/240 V line-voltage thermostat (baseboard heaters) from a 24 V low-voltage one, and which smart thermostats work with each.
• How to Replace a Thermostat Safely (Step by Step)The safe order of operations for swapping an old thermostat for a smart one: power off, photos, labels, wiring, and testing heat, cool and fan.