I'm upgrading from a failing ecobee smart thermostat to an ecobee3. The ecobee3 requires all wires for the components it controls to be run all the way to the thermostat (including humidifiers, dehumidifiers, etc).

I currently have 5 wires running to the unit, but I need the following for my setup:

  1. R
  2. G (fan control)
  3. Y1 (single stage cool)
  4. W1 (single stage heat)
  5. W2 (second stage heat)
  6. C (constant power for thermostat)
  7. ACC+ (humidifier)
  8. ACC- (humidifier)

Since I will be pulling new wire, I want to ensure I future-proof as much as possible for any future components I may add (such as a dehumidifier).


What thermostat wiring should I buy to get the maximum number of wires from the control board to the thermostat? What gauge/specs/etc?

I found 18/10 "sprinkler" wire on home depot's website. I also see that they have 18/8 thermostat wiring. Wondering what my options are and if it ever makes sense to run 2 sets of wires (such as an 18/8 and another 18/8).

1 Answer 1


Since your question relates to "future proofing," it all depends on where you think thermostat technology is headed. These days, I would not ever install less than 18/7 thermostat wire if I had a choice. This also happens to be the number of wires that you need for your setup if you tie your humidifier common to the system common and use the ecobee3 "1-wire configuration" for the accessory setup instead of using the 2-wire configuration that assigns the accessory terminals as independent dry contacts.

The future is probably digital. If you want to cover all likely residential possibilities then pull two cables, an 18/8 thermostat wire and a CAT5 (or better) network wire.

  • Great answer. Thanks so much for help. This is exactly what I was looking for.
    – Joe DePung
    Commented Oct 4, 2015 at 19:16
  • 3
    18/something and Cat5e/6 is a great answer. You could also install a conduit (eg 1/2" ENT) to pull a future cable, if ever needed (and if you do so, run the other wires outside the conduit, and leave the conduit either empty or with just a pull-string. Adding wire to conduit with existing wire is nearly impossible, and if you aren't using the existing wire anymore, it's probably obsolete and useless to retrieve anyway).
    – gregmac
    Commented Oct 5, 2015 at 17:45

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