Recently I replaced my aging thermostat with a new, smart, Nest thermostat, and I thought I’d quick capture a how-to for anyone who wants to do the same but probably doesn’t have the skills to do so.
- Remember your existing thermostat’s battery is dead.
- Replace the battery.
- Wonder why the new batteries refused to revive it. (Protip: You will never learn the answer.)
- Try various “reset” techniques.
- Decide you wanted a new smart thermostat anyway.
- Check that the existing wires coming out of the thermostat hole support smart thermostats.
- Realize they don’t.
- Google “Nest thermostat without the right wires”
- Learn about a “magical blue wire” that usually exists but is often hidden, tucked into the wall by lazy HVAC installers.
- Check the wall, find the blue wire. (Hooray!)
- Go to Target
- Acquire Nest Thermostat.
- Return home.
- Follow the directions that came with the Nest Thermostat.
- Wonder why it is also not working.
- Realize it’s new-in-box batteries are also dead.
- Ponder a future where batteries are no longer needed.
- Replace the batteries.
- Be thrilled it now works!
- Find a warning light in the Nest’s settings that says the “magical blue wire” isn’t connected correctly.
- Take the thermostat down.
- Re-strip the wire.
- Reconnect the wire.
- Reboot the Nest.
- Be taunted by the warning light’s continued presence.
- Swear. (Not required, but recommended.)
- Google “thermostat blue wire not working.”
- Discover those same lazy HVAC installers also sometimes don’t connect the blue wire to the furnace.
- Swear. (Again, not required. Still recommended.)
- Go down to your basement or wherever you keep your furnace.
- Search for the thermostat wires. (They are likely camouflaged with the other thousand wires in this part of your basement.)
- Hit head on joist. (Swear, required.)
- Find the blue wire, notice it is in fact dangling unconnected next to the furnace.
- Google “what should the blue wire be connected to?”
- Discover that the blue wire should be connected to the “common” port on the furnace’s control board.
- Take apart the furnace to find at the control board.
- Discover the control board already has a wire coming off the “common” port.
- Follow the wire.
- It goes to the Air Conditioner.
- Google “can I wire a Nest into the common port on my furnace if it’s already connected to an air conditioner”
- Discover a wiring diagram that says yes you can. (Hooray!)
- Start to wire everything per the diagram.
- Realize that the dangling blue wire is 4' too short to reach the furnace’s common port.
- Swear. (Louder this time, they should be able to hear you upstairs.)
- Debate with yourself for an indeterminate amount of time the merits of going to the store to acquire “official thermostat wire.”
- Decide not to, you probably have perfectly fine “wire” somewhere in the house.
- Remember an old spool of unnecessarily heavy gauge wire that’s probably “good enough” and retrieve it from a disused toolbox.
- Cut off 5' of it.
- Wire the dangling blue wire to the common port on the furnace using the new 5' wire.
- In a fit of unwarranted optimism, put the furnace back together.
- Return upstairs to the thermostat.
- Reboot it.
- Make sure the warning light is gone. (It is!)
Congrats! You now have a smart thermostat.
