Thermostat FAQs: 12 Questions Answered

How do I install a Nest thermostat?
How do I turn off auxiliary heat on a Honeywell thermostat?
How do you test a thermostat?
How can I tell if my thermostat is bad?
What is a millivolt thermostat?
What should I set my thermostat to in the winter?
How does a thermostat work?
How do you reset a thermostat?
What is a thermostat C wire?
What is the best smart thermostat?
What should I set my thermostat to when I am not home?
What does EMH mean on a thermostat?

How do I install a Nest thermostat?

To install a Nest thermostat, turn off the power to the system at the breaker first, remove the old thermostat, and photograph and label each wire before disconnecting. Mount the Nest base, connect the wires to the matching terminals, attach the display and restore power.

The app walks you through setup. The key check is compatibility: many systems need a C wire or a power adapter, and heat pumps, multi-stage systems and line voltage baseboard heaters need special wiring settings. If the wires do not match what the app expects, or if you see a high voltage wire, stop and call a licensed technician.

How do I turn off auxiliary heat on a Honeywell thermostat?

To turn off auxiliary heat on a Honeywell thermostat, use the System menu on most models. If it shows Emergency Heat, switch the system to Heat, or to Off, depending on what you want. Some models also have an auxiliary heat lockout or stage limit in the installer setup menu.

The menu steps vary by model, and the manual for your exact model number lists them. If aux heat keeps coming on during mild Arizona weather, the heat pump may be failing to keep up, so have a technician look at the system. Do not disable backup heat on a system that needs it.

How do you test a thermostat?

To test a thermostat, start with simple checks: fresh batteries, a clean display, and whether the system turns on when you set the temperature well above or below the room temperature. Then compare the thermostat reading to a second thermometer placed nearby.

If the thermostat is a wired model, a technician can test it by checking for 24 volt power at the control terminals and by jumping the correct terminals to see if the equipment responds. That should be done with the power off and by someone who knows the wiring. If the system runs when the terminals are jumped but not from the thermostat, the thermostat is likely the problem.

How can I tell if my thermostat is bad?

You can tell a thermostat is bad if it shows a blank or flickering display after you change the batteries, reads far from the actual room temperature, or leaves the system unable to start or stop. Short cycling, ignored settings and a lost schedule are other signs.

Before replacing it, check the breaker, the air filter, the batteries and the float switch on the condensate drain, since those can shut a system down and look like a thermostat problem. If the thermostat is working and the system is still off, the issue is somewhere else. A technician can sort it out quickly.

What is a millivolt thermostat?

A millivolt thermostat is a simple switch used with a gas appliance that makes its own tiny electric current, usually from a pilot light and a thermopile. It does not need power from the wall or batteries. It simply completes the circuit so the gas valve opens.

It is common in wall heaters and gas fireplaces. It is not a thermostat for a central air conditioner or heat pump, which uses low voltage 24 volt wiring, and putting the wrong type on a system will not work. If you are not sure which you have, check the appliance label or ask a technician before replacing it.

What should I set my thermostat to in the winter?

For winter, set your thermostat to a comfortable temperature and hold it steady, since constant adjustment wastes energy, especially with a heat pump. Many households settle somewhere in the high sixties to low seventies, and in the mild West Valley winters the heat may only run on early mornings and evenings.

Lowering it a few degrees when everyone is asleep or away saves energy. If you have a heat pump, avoid large setbacks, because the system may turn on backup heat to recover, which costs more. A programmable or smart thermostat can handle the schedule for you, which keeps the settings steady without constant adjusting.

How does a thermostat work?

A thermostat works by measuring the air temperature at its location and comparing it with the setting you chose. When the room is outside the range, it closes a circuit that tells the equipment to run. When the room reaches the target, it opens the circuit and the system stops.

In a typical home system, a low voltage 24 volt signal travels through thin wires to the air handler and outdoor unit, with different wires for cooling, heating and the fan. Newer models use digital sensors and software, and smart models add Wi-Fi, schedules and learning features.

How do you reset a thermostat?

How you reset a thermostat depends on the model, so check the manual for your exact thermostat. For most digital models, you can restart it by removing the batteries for a moment and putting them back, or by selecting a reset option in the menu.

Smart thermostats usually have a reset in settings, and some also require removing the display from its base. A reset can clear a frozen screen or a lost schedule, but it will also erase your programming. If the thermostat keeps losing power or the system still does not respond, check the batteries, the breaker and the wiring, or call a technician.

What is a thermostat C wire?

The thermostat C wire, or common wire, provides a continuous path for 24 volt power from the air handler's transformer to the thermostat. Basic thermostats do not need it, but Wi-Fi and smart models draw constant power and can behave erratically, drain batteries or reboot without it.

Many homes have an unused wire in the cable that can be connected as the C wire at both ends. If not, a technician can run new wire, add a power adapter kit or use a compatible accessory. Make sure power is off before touching the wires. Check the thermostat's compatibility checker before you buy.

What is the best smart thermostat?

The best smart thermostat is the one that works with your equipment and that you will actually use. Start with compatibility: check the wiring, whether it supports a heat pump, multi-stage equipment or a variable speed system, and whether a C wire is required.

Then consider the app, the schedule options, remote access, and whether it fits with the home systems you already use. Nest, Ecobee and Honeywell Home all make well known models, and each has strengths. For Arizona homes, features like remote control, high temperature alerts and filter reminders matter in summer. A contractor can tell you what works with your system.

What should I set my thermostat to when I am not home?

When you are not home in summer, set the thermostat a few degrees higher rather than turning the AC off, because a very hot house in the West Valley forces the system to run hard to recover. In winter, lower it a few degrees.

A modest setup saves energy without leaving the home unbearably hot, and pets, plants and electronics are a good reason to keep it reasonable. For heat pumps, avoid big swings that trigger backup heat. A smart or programmable thermostat can start cooling before you return. If you travel for a long time, a moderate setting is usually safer than turning it off.

What does EMH mean on a thermostat?

EMH, shown as EM HEAT, stands for emergency heat. It is a setting on heat pump thermostats that shuts off the heat pump and runs only the backup heat, usually electric heat strips or a furnace. It is meant for when the heat pump has failed, not for ordinary cold days.

You normally never touch AUX, because the thermostat manages it. Seeing AUX light up during a cold snap is typical, but seeing it all the time in mild weather is a sign to have the system checked.

Thermostats: 12 Most Asked Questions Answered