Heating & Cooling Thermostat Installation & wiring opening seal-up procedure:

Detailed photographs and text describe how to how seal a drafty opening in the wall at thermostat wires. Sealing air leaks around the thermostat wires improves the accuracy of the thermostat by stopping air leaks that can fool the thermostat about the temperature of the room it's supposed to be monitoring.

This article series provides detailed photographs and text describing how to how to install, make thermostat wiring connections.

Thermostat Installation: Close off Wall Opening Behind Thermostat to Improve Thermostat Accuracy

Close off large wall opening around thermostat wires

Below: if the wall opening through which the thermostat wires protrude is large, wall convection currents and drafts may foul up the thermostat's ability to accurately report and respond to room temperature. These images, from the installation of a Nest thermostat in a 1970's home show how to deal with that problem.

Above at left we see a stunningly large hole in the wall through which our thermostat wires emerge, and we are confronted by a plethora of old screw holes in the wall that make mounting one more new thermostat a devilish job. It would make a lot of sense to stop at this point and fill in all of these openings.

Watch out: When preparing your thermostat wires and before you start screwing the new thermostat mounting plate to the wall, if extra wire slack permits, be sure that you've pushed a loop of thermostat wire away from the wall surface inside the wall cavity.

This extra space and loose thermostat wires inside the wall cavity will reduce the chances that you drive a sharp-pointed thermostat5 base mounting screw through the thermostat wires, damaging them or even breaking or shorting the wires.

After pushing a loop of extra wire into the wall cavity we stuff some newsprint into the wall cavity to serve as a backer against which we'll apply a wall sealant product. How much newsprint? Enough that it will stay in place and provide a surface that avoids having to jam gallons and gallons of wall putty into that little hole while it drools down the back-side of the drywall or plaster instead of staying where we need it.

Our second photo shows me starting to apply wall putty to the biggest opening first. I like to use a fast-hardening product such as Dash Patch or a similar wall repair compound that sets in about 10 minutes.

I fill the large wall opening flush with the wall surface, actually slightly protruding past the wall surface, then I fill the smaller holes.

Watch out: As the wall patching compound begins to harden I use my putty knife to scrape away excess wall patch material to leave the patching material just flush with the wall surface. This is a nice detail to avoid having to scrape and sand hardened wall patching products.

Fast-setting wall patch compounds set quickly so you can complete your job in minutes, but if you don't work neatly you'll have a heck of a time trying to sand and scrape off too-high too-messy patch all over your wall surface.

Above, when the wall patch compound is firm but not fully hardened I use a damp paper towel to wipe off remnants of the patch compound to leave a smooth, ready-to-paint surface. No sanding whatsoever is needed if you take this approach. In my second photo I'm painting over this previously ugly, leaky wall with matching wall-paint.

Finally, when the matching wall paint is dry we are ready to hold the new thermostat base plate in place to mark its screw locations. Shown here we are installing a Nest 2 Learning Thermostat.

If you were reading this wall opening article while installing the Nest thermostat, continue reading those instructions at MARK WHERE SCREWS WILL GO.

For all other room thermostat wiring guides see THERMOSTAT WIRE CONNECTIONS.

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Continue reading at NEST THERMOSTAT INSTALLATION & WIRING, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• HUMIDITY RESPONSE, NEST THERMOSTATS
• TEMPERATURE RESPONSE of ROOM THERMOSTATS for more about thermostat accuracy
• THERMOSTAT CALIBRATION for details about adjusting the accuracy of room thermostats
• THERMOSTAT WIRE CONNECTIONS

Suggested citation for this web page

THERMOSTAT WIRING OPENING SEAL at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HVAC THERMOSTATS

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