In the HVAC world, thermostat wire is one of the most commonly used types of low-voltage cable – but not all thermostat wire is the same. Choosing the right conductor count (from 18/2 up to 18/10) ensures smooth installs, future-proofing, and fewer callbacks.
Here’s a breakdown of thermostat wire sizes from 18/2 to 18/10, and how each is used in residential, commercial, and multi-zone HVAC applications.
🔴 18/2 Thermostat Wire
Use Case:
- Simple heating-only systems
- Older furnaces or baseboard heaters
Wires Used: R (power), W (heat)
✅ Ideal for basic on/off heat applications.
🔵 18/3 Thermostat Wire
Use Case:
- Basic heat + fan or heat + cooling setups
- Older analog thermostats
Wires Used: R, W, G or R, W, Y
✅ Gives you a third wire for an extra function, like fan control.
🟡 18/4 Thermostat Wire
Use Case:
- Single-stage heat and cool systems
- Standard residential HVAC setups
Wires Used: R, W, Y, G
✅ Most common in homes. Supports heating, cooling, and fan functions.
🟢 18/5 Thermostat Wire
Use Case:
- Smart thermostats (Nest, Ecobee, Honeywell, etc.)
- Any system requiring a C wire (common for 24V power)
Wires Used: R, W, Y, G, C
✅ Future-proofs your install and avoids battery issues in smart thermostats.
⚪ 18/6 to 18/10 Thermostat Wire
Use Case:
- Multi-stage heating/cooling systems
- Heat pumps with auxiliary heat
- Humidifiers, dehumidifiers, or zoning systems
- Large commercial RTUs and control panels
Wires Used: Custom configurations for advanced control signals
✅ For pros who need flexibility and control – one cable handles it all.
🛠️ Installation Tips for Techs
- Always run extra conductors even if you don’t need them – they’ll save you a trip later.
- For multi-unit installs, bundle your thermostat wires cleanly and label both ends.
- Use plenum-rated wire (CMP) when running through return-air spaces.
- For long runs or high-EMI areas, consider shielded thermostat wire to reduce interference.
📦 Stocked and Ready – Thermostat Wire from 18/2 to 18/10
At Future Supply, we carry a full range of thermostat cable, including:
- Solid copper 18AWG wire
- From 2-conductor to 10-conductor
- Plenum and riser-rated jackets
- Available by the roll or in bulk
Perfect for HVAC contractors, control techs, and installers across Canada.
🧰 Need Help Choosing the Right Cable?
Give us a call or stop by—we know the job site, not just the specs.
Future Supply – Built for Techs. Trusted by Pros.
