How To Install a Programmable Thermostat

A programmable thermostat can improve your home’s energy efficiency without forgoing comfort. This upgrade allows you to automatically adjust your home’s temperature based on your schedule, potentially saving as much as 10% per year on heating and cooling bills, according to the Department of Energy. In the video above, This Old House plumbing and heating contractor, Richard Trethewey, shows how to install a programmable thermostat.

Types of Programmable Thermostats

There are several types of programmable thermostats. Each offers different features and programming options. Common types include the following:

• 7-day: Allows you to set a different schedule for each day of the week
• 5-2-day: Offers one schedule for weekdays and another for weekends.
• 5-1-1-day: Provides separate schedules for weekdays, Saturdays, and Sundays
• Smart thermostat: Connects to your home’s Wi-Fi network for remote control and learning capabilities.

Tools and Materials To Install a Programmable Thermostat

You’ll need the right tools before removing the old manual thermostat and replacing it with a programmable one. Get these tools and materials:

• Batteries (if required by your new thermostat)
• Drill/driver
• New programmable thermostat
• Screwdriver
• Torpedo level
• Wall anchors

Thermostat Installation Safety Precautions

While the wires connected to your thermostat typically carry low voltage, it’s always best to prioritize these safety measures:

• Turn off the power to your heating and cooling system at the circuit breaker or fuse box.
• Verify the power is off by attempting to adjust the temperature on your current thermostat.
• If you’re unsure about any step in the process, consult a professional HVAC technician.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, notes that while thermostat wires carry “low or no voltage,” he still recommends turning “the service switch off at the boiler downstairs” before beginning any thermostat work. Even low-voltage systems can cause unexpected issues if power isn’t fully disconnected.

How To Install a Programmable Thermostat

Follow our step-by-step instructions on how to install your new programmable thermostat.

Step 1: Remove the Old Thermostat

Here’s how to remove the old thermostat:

1. Remove the cover from your existing thermostat by gently pulling it off or unscrewing it.
2. Take a picture of the current wiring configuration for reference before unscrewing the thermostat from its wall-mounted sub-base.
3. Once you’ve carefully loosened the wires connected to the thermostat’s sub-base, remove the old sub-base from the wall.

Step 2: Mount the New Sub-base

Mount the new sub-base with these steps:

1. Hold the sub-base of the new thermostat against the wall, ensuring it’s level.
2. Mark the locations for the mounting screws.
3. Drill pilot holes for the screws if necessary, and insert wall anchors into the holes if needed.
4. Secure the sub-base to the wall using the provided screws.

Step 3: Connect the Wires

Most basic heating systems, such as the one Trethewey works on in the video, use only two wires. However, more complex systems may have additional wires. Refer to your thermostat’s instructions and the photo you took of the old wiring.

Important: Some programmable thermostats require at least three low-voltage wires — one to turn the furnace on, one to turn it off, and one to power the thermostat itself. If your existing setup has only two wires, check the new thermostat’s requirements carefully. According to This Old House Magazine, you may need to call an electrician or HVAC contractor to run an additional 18- or 22-gauge wire.

Here is how to connect a thermostat with two wires:

1. Connect the red wire to the “R” terminal on the new sub-base.
2. Connect the white wire to the “W” terminal.

Pro Tip: Richard Trethewey notes that on a basic heating system, polarity doesn’t matter: “It doesn’t matter which one is which, the red or the white, because it’s polarity insensitive.” This means you can connect either wire to either terminal without causing problems on a simple two-wire setup.

Step 4: Finalize the Installation

Once you connect the wires and the sub-base is securely mounted, complete the installation process as follows:

1. Insert the batteries into the thermostat if required.
2. Carefully attach the thermostat to the mounted sub-base.
3. Turn the power back on at the circuit breaker or fuse box.
4. Program the thermostat according to your schedule and preferences.

Programming Your New Thermostat

Programming your new thermostat maximizes its energy-saving potential. The Department of Energy recommends setting your thermostat to 78°F (26°C) in summer and 68°F (20°C) in winter when you’re awake and at home.

While the exact process may vary depending on your specific model, here are some general guidelines:

1. Set the current day and time.
2. Determine your weekly schedule and desired temperatures for different times of day.
3. Input your preferred temperatures for when you’re home, asleep, and away.
4. Take advantage of your thermostat’s energy-saving features, such as vacation mode or adaptive recovery.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, cautions that programming is the key step many homeowners skip: “Some of the first generation of programmables were painful to use. People got fed up. They’d just press the ‘hold’ button and do it manually.” Today’s digital thermostats are far easier to set up, with bigger displays and customized options — but only if you take the time to program them.

Enhancing Thermostat Performance

To get the most out of your new programmable thermostat, consider these tips for enhancing its performance:

• Location: Install the thermostat in a location that accurately reflects your home’s average temperature. Avoid placing it near drafts, direct sunlight, or appliances that emit heat.
• Optimal schedules: Experiment with different schedules to find what works best for your household. Perfecting the settings that provide the most comfort and energy savings may take time.
• Regular maintenance: Regular maintenance keeps your thermostat and HVAC system in top condition. Replace batteries as needed and clean the thermostat’s components to prevent dust buildup.

Troubleshooting Common Thermostat Issues

While installing a programmable thermostat is generally straightforward, you may encounter some issues. If you encounter persistent issues, don’t hesitate to consult a professional HVAC technician.

Here are some common problems and their solutions:

• Heating or cooling system not responding: Verify that the wires are correctly connected, there’s no corrosion on the wires, and your thermostat is compatible with your HVAC system.
• Inaccurate temperature readings: Ensure the thermostat is level and away from drafts or heat sources.
• Thermostat not turning on: Check the batteries or power connection.

Our Conclusion

Installing a programmable thermostat is a relatively simple DIY project that can lead to energy savings and improved home comfort. By following these steps and the guidance provided in Trethewey’s demonstration, most homeowners can successfully upgrade to a programmable thermostat.