Thermostat services: what to know

What the job involves, what changes the price, and what to ask a pro.

What thermostat services is

Thermostat services cover installing, replacing or troubleshooting thermostats, including smart models, the wiring behind them and their compatibility with your heating and cooling system. A thermostat that does not match the system can short cycle, run the wrong equipment or leave the house uncomfortable.

Signs you need it

  • The system does not turn on when the thermostat calls for heat or cool, or it runs the wrong mode.
  • The display is blank, flickers or resets after a power interruption.
  • The thermostat is old and has no wires for the system features you now have, such as a heat pump or a second stage.
  • The temperature on the thermostat does not match the temperature in the room.
  • You want a smart thermostat, and the existing wiring does not have the common wire it needs.
  • The system runs the backup heat or the wrong stage more than it should.

What the pro does

  • Turn off power and label each wire at the thermostat and the furnace or air handler before disconnecting anything.
  • Check the transformer voltage, the common wire and the control wiring for the system type.
  • Mount the new thermostat base and connect each wire to the matching terminal.
  • Set the system type, the heat pump settings, the stage and the fan options to match the equipment.
  • Test heating, cooling and fan operation, and check the thermostat's temperature against a reference reading.
  • Set up the schedule, the sensors or the zoning if the home has them, and show the homeowner how to use the controls.

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Thermostat type, such as basic, programmable, smart or zoned, with each adding its own wiring needs.
  • Whether the system is a heat pump, a dual-fuel system or a multi-stage furnace, which changes the settings and wires.
  • Whether the house has a common wire at the thermostat, or the wire has to be added.
  • Number of zones and remote sensors to be installed.
  • Access to the wiring, such as a plaster wall or a finished ceiling.
  • Whether the fault is in the thermostat or in the furnace, air handler or control board.
  • Whether a line-voltage thermostat for baseboard heat is being replaced, which is electrical work.

What a written quote should spell out

  • The thermostat model and the features it supports for this system.
  • The wiring work, including any new wire added and its gauge.
  • The system settings set during the install, such as heat pump, stage and fan options.
  • Whether sensors or zoning equipment are included.
  • Any repair to the furnace, air handler or control board, listed separately.
  • The warranty on the thermostat and on the wiring work.

Questions to ask before you hire

  • Will my system work with this thermostat, and which wires do I need to confirm that?
  • Do I have a common wire, or will you add one?
  • Will you set the heat pump and stage settings, or only mount the thermostat?
  • Will the thermostat work with my backup heat and my dual-fuel setup?
  • Will you test heating, cooling and the fan before you leave?
  • Who handles the warranty on the thermostat, and what does it cover?
  • Can you show me how to use the schedule and the remote settings?

Red flags

  • The pro installs a smart thermostat without checking the common wire or the system type.
  • The pro cannot explain which wires go where or why the settings were chosen.
  • The pro leaves the heat pump settings at their defaults without testing the backup heat.
  • The pro tests only one mode and says the system is fully working.

What you can do yourself

You can replace a basic low-voltage thermostat yourself if you turn off power at the furnace or air handler first, label or photograph every wire before you disconnect it, and match each wire to its terminal. Stop if the wires do not match your photos, if you see line-voltage wiring, or if the system is a heat pump with backup heat. Wire changes at the furnace or air handler belong to a licensed technician.

Licenses and permits

Thermostat installation is commonly done by licensed HVAC technicians, and line-voltage or electrical wiring may need a licensed electrician. Check with your state or local licensing agency for the requirements that apply to your installation.

Thermostat services questions

What is a common wire and do I need one?

The common wire, often labeled C, gives a smart thermostat steady power. Many smart thermostats need it. If your wiring does not include one, a technician can run a new wire or use another option.

Why does my heat pump thermostat switch to the backup heat so often?

The thermostat may be set with a recovery mode that calls for backup heat quickly, or the heat pump settings may be wrong. A technician checks the settings and the outdoor temperature sensor.

Can a smart thermostat save energy?

It can, if the schedule and the settings match how the home is used and the system is working correctly. A thermostat cannot fix a leaking duct or a failing system.

Why does my thermostat read a different temperature than the room?

The thermostat may be near a heat source, a window or a supply register, or the sensor may be out of calibration. A technician can check the reading and move or adjust the sensor.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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