Tools & materials
- New thermostat
- Screwdriver
- Phone for photos
- Wire labels (usually in the box)
- Drill (for new mounting holes)
Step by step
- Step 1
Turn off power to the furnace/air handler at its switch or breaker.
- Step 2
Remove the old thermostat cover and photograph the wiring and terminal letters (R, W, Y, G, C).
- Step 3
Label each wire with the matching sticker before disconnecting.
- Step 4
Remove the old base, feed the wires through the new base and mount it level.
- Step 5
Connect each wire to the matching terminal on the new base, then attach the thermostat.
- Step 6
Restore power, set up the system type and test heat, cool and fan.
When to stop and call ProFix
If you see any of these, stop and call us:
- The old thermostat has thick wires or says 120V/240V (line voltage, common on baseboard heat)
- You have a heat pump or multi-stage system and aren't sure of the setup
- There's no C-wire and your smart thermostat needs one
Not in the mood to DIY? A ProFix pro can handle it for you in Chicago Metro and Dallas–Fort Worth, with a written price before work starts.
Related guides
These guides are general information for simple repairs. You're responsible for your own safety and for following local codes and your lease or HOA rules. When in doubt, stop and call a licensed professional. All DIY guides