How to Replace a Thermostat
Purchase a replacement thermostat that will work with your system., Review the manufacturer instructions for wiring your replacement thermostat., Shut off the power to your thermostat., Remove the old thermostat from the wall., Pay attention to how...
Step-by-Step Guide
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Step 1: Purchase a replacement thermostat that will work with your system.
Review the compatibilities listed on the packaging of the replacement thermostat.
Most replacement thermostats are compatible with all common systems.
However, if your system is unique, finding a replacement thermostat may be difficult.
Here are your basic options (information that should be easily found on the packaging):"Works with 1 stage heating or cooling":
Used when you have separate heating and air conditioning units "Works with 2 stage or multi-stage heating or cooling":
Used for heating or cooling units that have designated high and low speeds "Works with Direct Line Voltage":
Used with 110 or 240 direct current power sources to power the thermostat (generally seen in older homes) "Works with 24mV":
Used with fireplaces, floors, or wall furnaces "Zoned HVAC":
Used when both heating and cooling are individually controlled in different areas from the same system -
Step 2: Review the manufacturer instructions for wiring your replacement thermostat.
Most thermostats utilize similar installation methods; however, it's beneficial to read all materials and preview all pictures provided for how to install your new thermostat.
Or you risk literally being stuck in the cold! Reading instructions is a total drag, yes.
But this is not something you want to mess up! Read them and study the pictures.
You want yours to match detail for detail.
It’s also a smart idea to always take pictures of the existing wiring before you start. , Turn the switches off at the breaker box that pertain to your thermostat, furnace and air conditioner.
Turning off the power to the thermostat reduces the chances of electrical injuries as you remove the old thermostat and install the new one. , Most thermostats slide upward from where they are attached to the wall.
Loosen the screws that attach the wall plate to the wall, if there is one.
Some thermostats have a base and sub-base.
You need to remove the entire thermostat
-- all you should be left with is exposed wires and a bare wall, nothing else.
If the wires you expose are corroded and there is enough wire length, re-strip the wires.
Otherwise, scrape the ends with a utility knife until they are shiny. , This is the most important step.
Most thermostats wires are coded, but some (if done by an amateur previously) can be coded incorrectly.
To make sure you're doing it right:
With a piece of tape, write a letter on each wire, matching the letter of the connection on the thermostat base.
If the blue wire was in connection B, write "B" on the piece of tape, and put the tape on the wire.
Label or designate any wires that were loose and unconnected to your thermostat as well.
Ignore the colors of wires, except for your own identification purposes.
Thermostats wired by non-professionals do not usually adhere to codes, so the colors may not match what they should. , Tie the wires together or tape them to the wall to keep them from falling back into the wall.
A lost wire will turn this rather easy process into quite the debacle.
Pro tip? Wrap all the wires around a pencil.
The weight of the pencil is just enough to keep the wires from going anywhere. , Use the new wall plate as a template to mark where the holes you need to drill for the screws will be.
Use a level if necessary.
Then, drill the holes, and screw the replacement wall plate into its new position on the wall.
If your new thermostat has a mercury tube (that is to say, if your new thermostat is rather old school), your device needs to be completely level or it won't render accurate readings.
Using a level is very important in this scenario and is not just for aesthetic reasons.
Make sure you're drilling holes that match the size of your screws.
A 3/16" drill bit is fairly standard.
Your thermostat definitely comes with screws, and probably comes with anchors.
Make sure to use the anchors, too.
They support the system on the wall. , Use your notes or labels to re-connect the wires to the thermostat – or, follow the pictures you took of the pre-existing wiring.
You can twist the wires onto the thermostats connectors, or follow the directions manual provided by the manufacturer.
Your new thermostat should have the same corresponding code on the back, unless otherwise noted in the instructions.
If you're at all in doubt, contact a heating and cooling company.
Some thermostats are as simple as a two-wire system.
Some have
5.
If you have empty ports or connections, don't worry.
Your thermostat is most likely fine. , Replace all wires back into the wall, if extra length is exposed.
Place the thermostat flush against the wall, slightly above the wall plate.
Slide it down so it catches the grooves (or screws) on the wall plate to sit in place.
If your thermostat isn't in a good location (it's exposed to drafts or heat, which can mess up the readings, or it's too high or low for you), you'll need to contact a professional to have wires moved. , Switch on the proper switches in the breaker box to restore power.
Give it a minute to kick on.
And don't forget to install the batteries! Most systems require 2 AA batteries to work.
Make sure the batteries aren't old, they're in place, and the polarities are correct , Set the thermostat so the furnace and the air conditioner will come on at different times.
Give your furnace and air conditioner at least 5 minutes each time to activate.
If the thermostat does not work properly, retrace your steps to see where you made a mistake.
You may need to hit the reset button on your new thermostat.
Some will not start until this button is pushed. , Each type of thermostat is different, so read your manual if you have questions.
Just remember that a programmable thermostat can save you loads of money
-- have it be cooler when you're gone and warmer when you're there.
It'll turn off without you, saving you money and saving energy to boot! -
Step 3: Shut off the power to your thermostat.
-
Step 4: Remove the old thermostat from the wall.
-
Step 5: Pay attention to how the old thermostat was wired as you disconnect it.
-
Step 6: Keep the disconnected wires hanging out of the wall.
-
Step 7: Install the replacement wall plate.
-
Step 8: Hook up the thermostat to the wires.
-
Step 9: Place the thermostat on the wall.
-
Step 10: Activate the power back to the thermostat
-
Step 11: furnace and air conditioner.
-
Step 12: Check to make sure your replacement thermostat is working.
-
Step 13: Program your thermostat.
Detailed Guide
Review the compatibilities listed on the packaging of the replacement thermostat.
Most replacement thermostats are compatible with all common systems.
However, if your system is unique, finding a replacement thermostat may be difficult.
Here are your basic options (information that should be easily found on the packaging):"Works with 1 stage heating or cooling":
Used when you have separate heating and air conditioning units "Works with 2 stage or multi-stage heating or cooling":
Used for heating or cooling units that have designated high and low speeds "Works with Direct Line Voltage":
Used with 110 or 240 direct current power sources to power the thermostat (generally seen in older homes) "Works with 24mV":
Used with fireplaces, floors, or wall furnaces "Zoned HVAC":
Used when both heating and cooling are individually controlled in different areas from the same system
Most thermostats utilize similar installation methods; however, it's beneficial to read all materials and preview all pictures provided for how to install your new thermostat.
Or you risk literally being stuck in the cold! Reading instructions is a total drag, yes.
But this is not something you want to mess up! Read them and study the pictures.
You want yours to match detail for detail.
It’s also a smart idea to always take pictures of the existing wiring before you start. , Turn the switches off at the breaker box that pertain to your thermostat, furnace and air conditioner.
Turning off the power to the thermostat reduces the chances of electrical injuries as you remove the old thermostat and install the new one. , Most thermostats slide upward from where they are attached to the wall.
Loosen the screws that attach the wall plate to the wall, if there is one.
Some thermostats have a base and sub-base.
You need to remove the entire thermostat
-- all you should be left with is exposed wires and a bare wall, nothing else.
If the wires you expose are corroded and there is enough wire length, re-strip the wires.
Otherwise, scrape the ends with a utility knife until they are shiny. , This is the most important step.
Most thermostats wires are coded, but some (if done by an amateur previously) can be coded incorrectly.
To make sure you're doing it right:
With a piece of tape, write a letter on each wire, matching the letter of the connection on the thermostat base.
If the blue wire was in connection B, write "B" on the piece of tape, and put the tape on the wire.
Label or designate any wires that were loose and unconnected to your thermostat as well.
Ignore the colors of wires, except for your own identification purposes.
Thermostats wired by non-professionals do not usually adhere to codes, so the colors may not match what they should. , Tie the wires together or tape them to the wall to keep them from falling back into the wall.
A lost wire will turn this rather easy process into quite the debacle.
Pro tip? Wrap all the wires around a pencil.
The weight of the pencil is just enough to keep the wires from going anywhere. , Use the new wall plate as a template to mark where the holes you need to drill for the screws will be.
Use a level if necessary.
Then, drill the holes, and screw the replacement wall plate into its new position on the wall.
If your new thermostat has a mercury tube (that is to say, if your new thermostat is rather old school), your device needs to be completely level or it won't render accurate readings.
Using a level is very important in this scenario and is not just for aesthetic reasons.
Make sure you're drilling holes that match the size of your screws.
A 3/16" drill bit is fairly standard.
Your thermostat definitely comes with screws, and probably comes with anchors.
Make sure to use the anchors, too.
They support the system on the wall. , Use your notes or labels to re-connect the wires to the thermostat – or, follow the pictures you took of the pre-existing wiring.
You can twist the wires onto the thermostats connectors, or follow the directions manual provided by the manufacturer.
Your new thermostat should have the same corresponding code on the back, unless otherwise noted in the instructions.
If you're at all in doubt, contact a heating and cooling company.
Some thermostats are as simple as a two-wire system.
Some have
5.
If you have empty ports or connections, don't worry.
Your thermostat is most likely fine. , Replace all wires back into the wall, if extra length is exposed.
Place the thermostat flush against the wall, slightly above the wall plate.
Slide it down so it catches the grooves (or screws) on the wall plate to sit in place.
If your thermostat isn't in a good location (it's exposed to drafts or heat, which can mess up the readings, or it's too high or low for you), you'll need to contact a professional to have wires moved. , Switch on the proper switches in the breaker box to restore power.
Give it a minute to kick on.
And don't forget to install the batteries! Most systems require 2 AA batteries to work.
Make sure the batteries aren't old, they're in place, and the polarities are correct , Set the thermostat so the furnace and the air conditioner will come on at different times.
Give your furnace and air conditioner at least 5 minutes each time to activate.
If the thermostat does not work properly, retrace your steps to see where you made a mistake.
You may need to hit the reset button on your new thermostat.
Some will not start until this button is pushed. , Each type of thermostat is different, so read your manual if you have questions.
Just remember that a programmable thermostat can save you loads of money
-- have it be cooler when you're gone and warmer when you're there.
It'll turn off without you, saving you money and saving energy to boot!
About the Author
Timothy Ramirez
Specializes in breaking down complex lifestyle topics into simple steps.
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