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DIY Smart Thermostat Install Goes Wrong

Google’s NEST Learning Thermostat

I love do-it-yourself projects! It’s a great way to save money, and I believe every homeowner should be self-reliant. When it comes to changing thermostats there’s online sources like this one at The Home Depot and this informative post about choosing Thermostats.

Many sites advocate that you (the homeowner) should easily be able to switch out your own thermostat. Well don’t let me tell you otherwise. You can, but please read a story of warning.

Pictured above you’ll see the latest and greatest in home thermostats: the NEST Learning Thermostat by Google. It’s easy to use, easy to install, hooks up to Wi-Fi, and can be controlled by your smart phone wherever you are in the world.

However, it can still be installed wrong.

My customer’s furnace wasn’t heating. It was running, just not heating. When I showed up I quickly realized a dangerous situation. His A/C system was running while it was 31 degrees F outside! Certainly not heating the house, but also potentially damaging the outdoor compressor. The typical A/C compressor isn’t designed to run in temperatures below 58F. This is why home inspectors are warned to not test A/C units in temps below 60F.

Thermostat’s like the NEST can be wired for heat pumps or standard A/C’s. They can do it all! This smart, little thermostat probably walked my customer through the installation process. Typically it asks questions, and how you answer those questions determines which wires go where.

Unfortunately my customer didn’t know the difference between a heat pump and an A/C. He wired his unit as a heat pump, and naturally the thermostat told his compressor to turn on for heating the home. That’s what it’s supposed to do. Heat pumps can run in cold weather. However, the typical A/C don’t have the necessary gear to ensure safe operation at low temperatures.

In short, one little wire can destroy your A/C. If you have any doubts about wiring a thermostat, please call a certified HVAC tech. You might pay him/her a couple hundred dollars, but according to Home Advisor replacing an A/C compressor can cost between $800-$2800. It’s all dependent on your unit brand and size, but as an HVAC professional I can tell you those figures are accurate.

If in doubt, just don’t risk it. Call a pro.


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