How to Install a Programmable Thermostat

If your weekday schedule varies from your weekend schedule, a 5-1-1 thermostat can save you money. "5-1-1" refers to the fact that such thermostats let you set a weekday schedule and a Saturday/Sunday schedule independently. If you've always wanted to install a programmable thermostat, but have been intimidated by the thought of any DIY project that involves wires, look no further. Safely installing a programmable thermostat in your home doesn't need to be something that leaves you steaming - see Step 1 below to get started.

Disclaimer: The following instructions are for inspirational purposes only, and are not meant to substitute manufacturer instructions that come with your particular model.


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    Review the instructions included with the new thermostat. This is an important step - even if you do not understand everything you are reading. Some thermostats have a few straight-forward options that are set by jumper(s), switch(es), etc. that help it work properly with your particular heating system. A common such setting is one that selects GAS or ELECTRIC heat.
    • Failure to select the proper setting is an avoidable problem if you take the time to read the manual first. Most reputable manufacturers that sell thermostat models at hardware stores, "big box" stores, etc. will usually include a combination of one or more: email address, website and even a telephone number you can call if you need help. Nearly always both the call and help are free.
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    Make sure you select a thermostat that matches the control voltage of your heating system. There are basically just two types: a "line voltage" type that works with heating system control voltages of 120 volts or more and, a "low voltage" type that works with heating system control voltages around 30 volts or less. Most low voltage types use small #18 gauge wires (like those on a doorbell button or chime unit) while "line voltage" types use traditional #14 and #12 gauge "building" wire sizes (like those used to connect outlets, switches and light fixtures).
    • To be absolutely sure about which type is used in your home, bring the old thermostat into the store you will purchase the replacement (leave the base plate with wiring in place or be sure to label or photograph wires before disconnecting) and ask an employee for assistance. If you can't bring the thermostat in - consider taking a couple of digital photos of it with a camera or cell phone. If possible, take a photo that shows your thermostat manufacturer's name and model number.
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    Determine if you need a "Heating Only" or "Heating and Cooling" thermostat. If the thermostat only controls the of heat in your home, you can save money by selecting a "Heating Only" thermostat. These thermostats are often nearly identical in appearance to their "Heating and Cooling" counterparts, but cost less because they do not include the additional circuitry and components needed to control a central air conditioning system. It is important to understand that both thermostats are functionally identical when working in Heat mode.
    • Purchase a "Heating and Cooling" thermostat only if your old thermostat controls both the heating and cooling, if the thermostat you have selected is not available in a "Heating Only" version or you currently use the thermostat to control only heat - and: a.) plan to add air conditioning soon and b.) would like to control it from the same thermostat.
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    Turn off all power at main electrical panel. Some instructions advise to simply turn off power to the room you are working in, others suggest throwing the main switch. To lean towards safety, turn everything you can find on the electrical panel to the “Off” position.
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    Remove cover and control panel from old thermostat. The cover and control board on most models snap off. Look for a recessed lip around the sides or bottom of the original thermostat where you can grab and remove the faceplate and control board. Take care setting this aside as you may have to reinstall if something goes wrong further in the installation.
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    Label wires according to their current position, and remove them one by one. Most new models of programmable thermostats come with sticker labels that you can use to wrap around the wires coming from the wall. If your package doesn’t contain pre-printed labels you can substitute with masking tape and a permanent marker.
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    Remove old thermostat base plate from the wall. Be sure not to let the mess of wires drop back into the wall when unscrewing the old base plate. Some instructions recommend taping a group of wires to the wall, but if the wires are so stiff that simply spreading them out a bit adequately prevents them from dropping back into the hole in the drywall, this shouldn't be necessary.
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    Secure the new thermostat base plate to the wall. Most of the time a new model’s base plate will not match up to the existing holes from the old thermostat. If so, simply drill a couple holes for the new thermostat, and insert the drywall anchors that came in the new packaging (don’t worry, the instructions should account for this by indicating the drill bit size to use, etc.).
    • Go ahead and insert batteries if your model requires them. The model used in this example required two AA batteries (installed just above the wire connections), others use the base plate only to support the thermostat and for wire terminal connections. The batteries would be installed in the thermostat itself.
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    Reattach the wires according to their label and the corresponding spot on the new thermostat base plate or to the thermostat directly - depending on the model you have. This may very well be the most difficult part of the entire project because there isn’t much room to work with, and depending on your heating/air conditioning system you could have several wires to attach.
    • If your previous thermostat was a non-battery operated and the new one takes batteries you may have one wire from furnace that is not needed. 24v negative. This will usually be a blue wire. Tape off and leave disconnected. This is to power a digital non-battery type thermostat and is not needed if your new one uses battery.
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    Attach control panel and faceplate for new thermostat. Make a handwritten note of the wires you attached (C, G, Y, R, etc.) before covering with the new control panel and faceplate. You’ll need to know this to properly program your new thermostat based on the type of system you have.
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    Turn power back on and program new thermostat according to manufacturer instructions. In the summer time, you might choose to let the temp get a little higher at night and sleep with ceiling fans running. Before you wake up, program the thermostat to cool things down for getting ready for work and school, and then return to a higher temperature for the day. In the winter, reverse this process by letting things cool down after you are tucked away in bed, and warm things up during the early morning hours.


  • Program thermostat prior to installing onto base. Many thermostats require batteries to keep time, run the program, maintain settings, etc. when used in "millivolt" and "microvolt" (these are common "extremely low" voltage) systems and during power outages. If the batteries are installed in the thermostat itself and not the base, this programming tip should work. Install the batteries in the thermostat and then check the display. If there is an indication on the display (time or temperature), attempt programming from the comfort of your favorite chair or at a desk or table. This should also work when replacing dead batteries or anytime the program needs to be changed significantly or re-entered.


  • Older thermostats might have glass tubes that contain mercury, so be careful when handling and disposing of them.[1]

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