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When Should I Replace My Thermostat Wire?

It’s time to replace your thermostat wire if your HVAC system requires different voltage or if your current wiring bundle can’t handle a new HVAC system’s performance capacity. If you’re switching your HVAC system from a 110V system to a 240V system or replacing a single-stage system with a two-stage system, it’s smart to replace your thermostat so it can work properly with any new components.

Type of Wire

A thermostat wire size is 18 gauge and can come with 10 or more wires. Once you determine the number of wires needed for your HVAC system, it’s a good idea to add two spares to give you more flexibility in the future. Most HVAC systems require 5 or more wires if both heating and cooling are involved.

Each wire matters, so make sure to talk to your certified technician. A c-wire, for example, can monitor the indoor and outdoor temperatures as well as other climate features.

Relocating Your Replacement

If you’re relocating your thermostat or installing a new one, its home should be as comfortable as yours. Thermostats should be installed on interior walls because exterior walls are cooler in the winter and warmer in the summer, which can affect your thermostat readings. The best spot for a central forced air system is close to a central return grill.

You’ll want to install your thermostat and its wiring in a place where it can avoid:

  • Direct sunlight

  • Drafts from doors and windows

  • Heat or steam from bathrooms

  • Heat from other appliances

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