Is Your Smart Thermostat Slowly Killing Your HVAC System?
Doesn’t your thermostat require a C-Wire? Here’s the truth
Most new smart thermostats come with a Li-ion battery which needs to be recharged as it operates. In fact, this battery has more heavy lifting to do than one may think. Outside of its primary job of sending instructions to your HVAC system, it has to run the operating system, motion sensing wake sleep commands, back-lighting, constant wifi connection, geofencing, and more. These features all nibble away at battery life little by little. In order to keep the battery juiced up, the thermostat constantly seeks for a power source.
Enter in the Common Wire, or “C-Wire”
In years past, thermostats simply were on/off devices that either required no power, or a simply needed no more than a few AA batteries. With the rise of thermostats requiring more power for digital displays, scheduling, and other features, the need for constant power was evident. The C-Wire allows the 24 volts of power flowing from the transformer at your HVAC system, via the R (red) wire, to flow continuously. Once you have a C-wire, you’re in business. But many of us are in older wiring homes, condemned to a domicile in C-wire purgatory; the dreaded 2 wire system, or other non-C-wire configurations. This is where your problems begin.
What’s the issue?
Now Nest and some other smart thermostats promise that you can use their product without a C-wire; “you’re fine they say”. Now here’s the truth, in the absence of the C-Wire, the thermostat acquires power from the HVAC system, “power stealing”, even when cooling or heating systems are not active. Remember it was mentioned above that your HVAC systems has a built in 24-volt transformer via the R wire. The thermostat will cycle your HVAC system on and off in a pulse-like fashion in order to acquire this power. Although these pulses can be brief, they can consume a notable amount of power, and needlessly cycles your system. I think we all remember when we were kids and would turn the light switch off and on in rapid succession, now do we remember what happened to light bulbs if we did this too much?
See this post on Reddit from HVAC tech warning people about smart thermostats and the dangers it can present to your HVAC system overworking the system due to power stealing.
Is there a way to fix this issue?
In fact, there is more than one fix for this issue. For the benefit of our readers, we will list those fixes below. Please note that the efficiency of these fixes might vary and try them at your own risk.
As the summer approaches, find the heat wire (W) to C terminal. During winter, however, C terminal should be connected with the cooling wire (Y). Although this is practical, we don’t think it is a very efficient method. After all, switching your wires during every climate change can be daunting.
As the second option, you can try connecting “G” (Fan Wire) with the C terminal. However, with this method, you cannot necessarily use the fan alone. The fan has to run when the system is functioning. Needless to say, that this is not a great option.
Both of the above options require constant hacks on your part. Also, the second option doesn’t let you have the fullest control of the fan. Honestly, we cannot recommend these so called ‘solutions’ to our readers. The recommendation is a better and more permanent solution.
OKAY then, what is the best fix for this issue?
Get new wiring (connect your furnace and the thermostat unit) with the assistance of a professional. I know, all this reading just to state the obvious? And that’s not why you’re here to read this in the first place, is it?
Fix 02 (The best of all):
Get an external power supply unit and install it in your system. Having an external power supply to your thermostat will keep its battery charged full time without interfering with the functionality of your HVAC system. This approach will prolong the lifespan of your system, as well as saving energy.
Connecting this external transformer to a standard outlet and wiring to your "C" terminal can give you the piece of mind of powering your thermostat independently of your HVAC system.