Introduction to programmable thermostat installation
If you have some experience with DIY and electrical wiring in your home it should not be too difficult to install a digital programmable thermostat in your home. The easiest type of installation is to replace one digital thermostat with another. The hardest is to replace a mechanical thermostat with a digital thermostat. Also some thermostats such as the Honeywell Prestige HD also require the installation of an outdoor sensor and possibly require connection to humidity control devices.
The very first thing you should do, even before getting your tools out, is to read the instruction manual carefully that comes with your new digital programmable thermostat. We’ve included links down the right for some instruction manuals in case you lose the manual.
The next thing to decide is whether your house is a single zone or multi zone house. Most houses have just one HVAC system and thus require just one programmable thermostat. Bigger houses might have 2 or more furnaces etc. and will require a programmable thermostat for each zone.
Where to place a programmable Thermostat
Another important consideration is where to put a digital programmable thermostat. Usually you will put the thermostat in the same place as the old one to cover the hole. There is, however, a possibility that the last thermostat was put in the wrong place (or that the room has been renovated and changed and that what was once the ‘right place’ is now the wrong place). Here is a check list of WHERE NOT TO PUT A PROGRAMMABLE THERMOSTAT
- Never put it near a fireplace or on the same wall as a fireplace. This is always the case even if the fireplace is inoperable.
- Never put the thermostat on an outside wall.
- Never put the thermostat in a place where the sun shines directly on it as this will affect the accuracy of the thermostat.
If you find that your old thermostat breaks any of these rules you will have to run the wires from your old thermostat to a more suitable location for the installation of your new programmable thermostat.
Programmable Thermostat installation guidelines
The most important thing to do before starting the job of replacing a thermostat is to turn off the power at the breakers. Even though the voltage going to a thermostat is low you don’t want to have a shock or damage your HVAC by forgetting to turn off the power.
Now you are ready to install a programmable thermostat. Take the front cover off the old thermostat and then unscrew the sub-base or wall plate and take the thermostat off the wall. At this stage do not un-attach any of the wires. You must study the wiring of the old thermostat and use this as the basis for wiring your new programmable thermostat. It is a good idea to have some sticky tape nearby so you can mark the wires so you know exactly what color they are.
It is sometimes the case that the wire colors are faded or that they are wrongly colored. To ascertain the correct color for each wire check with the back of the old thermostat to see which terminal it is connected to. If your old thermostat worked fine then you must continue to follow the same coloring system.
Once you are sure the correct color designation for a wire then tape it (writing the color on the tape) and then unscrew it from the old thermostat. Wrap the wire around a pencil to stop it falling down into the wall cavity.
One all the wires have been taped and coiled around pencils you can drill holes for the new wall plate and attach the wall plate. Next consult the instruction manual carefully and screw the wires onto the back of the new programmable thermostat.
Next put batteries into the new thermostat and then you are ready to start programming your new digital programmable thermostat. Turn the power back on and try out the fan, heat and air-con separately to make sure they are all working. If all is good then it is time to start inputting your set point temperatures and times.
Red is the ‘hot’ wire from the transformer
Green is the fan
Yellow is the air-conditioner
White is the heat
Red is sometimes marked RC or RH
Make sure the live wires do not touch anything except the terminal that they are attached to.
Sometimes it is necessary to note the heat anticipator setting from the old thermostat. Most programmable thermostats set the heat anticipator automatically. Again check in the instruction manual.
Tape up the ends of any wires not used.
Video showing how to install a programmable thermostat
This video by Home Depot clearly shows how to install a programmable thermostat.