Is the Helio T2 compatible with my HVAC system?

The Helio T2 works with the large majority of North American 24 V systems. Use this page to check yours before ordering or installing.

Supported

Gas, oil and electric forced-air furnaces (1 or 2 heat stages)
Central air conditioning (1 or 2 cool stages)
Heat pumps with auxiliary/emergency heat (O or B reversing valve)
Boilers and radiant systems with a 24 V control (single stage)
Fan-only control (G)

Not supported

Line-voltage systems (120/240 V) such as electric baseboard heaters and wall heaters. These need a line-voltage thermostat.
Millivolt gas fireplaces and wall furnaces.
Proprietary communicating systems (some Carrier Infinity, Bryant Evolution, Trane ComfortLink) unless the installer adds a standard 24 V interface.
Systems with more than 2 heat + 2 cool stages.

The C-wire

The T2 draws power through the C (common) wire. If your old thermostat has a wire on the C terminal, you are ready.

If not:

Look behind the old thermostat for an unused wire tucked into the wall. Often a blue or black wire is present but not connected; it can usually be connected at the furnace control board as C.
If there is no spare wire, use the Helio Power Bridge (included in the box). It installs at the furnace control board in about 10 minutes and creates a C connection using the existing wires.
The T2 does not support "power stealing" without a C-wire. Running it that way will cause short-cycling and reconnects.

Quick check

In the Helio app, tap Add device → Check compatibility, enter the labels on your current thermostat's wires, and the app tells you which case you are in before you take anything off the wall.

If you are unsure at any step, stop and contact support with a photo of your current wiring. We will tell you exactly which terminals to use.