Last updated on September 9th, 2017
Problem: Your HVAC system lacks a C-wire (common wire) for your new WiFi thermostat
Solution: Install a Venstar Add-a-Wire adapter!
Venstar Add-a-Wire Adapter: a Simple Solution to a “Common” Problem
Short a wire?
If you are lacking the (ironically named) “common wire”, also known as the C-wire, you might be pleased to learn that there’s an adapter for that.
The Venstar Add-a-Wire is an inexpensive, DIY-friendly alternative to running completely new HVAC wires.
Why add a wire?
In short, Wi-Fi thermostats need more power to run that always-on Wi-Fi connection. The C-wire a common wire that delivers a continuous flow of electricity to your thermostat.
Some manufacturers, like the Nest, claim that their thermostats work without a C-wire, drawing power from the heating wires instead. Unfortunately for many homeowners, the outcome is an intermittent WiFi connection or unwanted furnace cycling.
If you have a low voltage HVAC system, you can skip some of the hassle if you select a thermostat that works without a C-wire or ships with an adapter.
- Ecobee thermostats, including the ecobee4, ecobee3, ecobee3 lite all come with their own Power Extender Kit that you can set up yourself inside your furnace
- Emerson Sensi is a low-power smart thermostat designed to work without a C-wire in systems that include both heating and cooling
All ecobee thermostats ship with a super handy “power extender kit” (PEK for short). In the photo below, an ecobee3-style PEK (in my hand) and an ecobee4-style PEK (in the background). They are functionally identical.
If you’re not sure what you have or what to do with your wiring, check out our full guide to the C-wire.
Unboxing the Venstar Add-a-Wire
In the box:
- Venstar Add-a-Wire unit with wires
- Additional wires
- Installation guide
- Two twist-on electrical caps
Venstar Add-a-Wire Installation
Adding an adapter is not difficult: if you’ve ever installed a ceiling lamp or replaced an electrical outlet, you’ve got the skills and tools for adding this adapter.
Most of the work is in twisting wires together and matching colors. Installation takes first-timers about an hour, start to finish. Instructions are included with the adapter.
- Phillips screwdrivers
- Electrical tape
- Needle nose pliers
- Drill / drill bit
- 2 wire nuts (included)
You will need access to both your furnace wiring and your thermostat wiring. You’ll be installing new wire parts at your furnace and behind your thermostat.
This five minute video made by Venstar’s manufacturer demonstrates the installation process. If you are considering buying this adapter, watch this video first to see the full scope of the project:
Expect a little ambiguity as your furnace panel will invariably vary from the one shown, but anyone savvy enough to install the thermostat itself should be able to handle this project.
We highly recommend the Venstar Add-a-Wire adapter. It’s much cheaper and easier than running new HVAC wiring, can be done by almost anyone in about an hour, and well-reviewed by other buyers on Amazon.com.