Honeywell digital room thermostat (C) Daniel FriedmanHVAC Thermostat Settings
How to set or adjust the heating or cooling thermostat in buildings

  • THERMOSTAT SET PROCEDURE - CONTENTS: how to set or adjust a room thermostat used for heating or cooling. How digital room thermostats work & what the displays mean. How to see the "set" temperature vs. the actual or current room temperature on a thermostat. THERMOSTAT SET to DESIRED TEMPERATURE - HOW DIGITAL THERMOSTATS WORK
  • POST a QUESTION or READ FAQs about line voltage thermostats
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Heating or cooling room settings: how to adjust the room thermostat for heating or air conditioning: how to set the thermostat to the desired temperature & how to diagnose thermostat setting problems. We describe how to find the current room temperature and how to compare it to the set temperature or target temperature on the thermostat.

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Heating & Cooling Control Thermostat Setting Guide

Nest learning thermostat showing programming mode - at Home Depot displayUsing Wall-Mounted Room Thermostats - How to Set the Thermostat

Detailed photos of the major components of a wall thermostat and a description of how heating & cooling thermostats work are provided below. If your heating system is not working at all, start at HEAT WON'T TURN ON.

Remote Control Thermostats & Remote Heat, Cooling, or Building Temperature Monitoring

A variety of remote control thermostats are offered by HVAC control manufacturers, permitting an owner to monitor, or even change building temperature control settings remotely by telephone or by web-enabled internet connection.



Proliphix provides a range of energy control thermostats that offer remote temperature control via web-enabled communication between an individual and the building's HVAC controls.

Also see Honeywell Controls, and White Rodgers thermostat controls documents at REFERENCES

NEST ROOM THERMOSTATS (shown at above left) are a top-end programmable room thermostat that can be controlled remotely by cellphone.

How to Set a Room Thermostat To the Desired Temperature

Honeywell room thermostatHere is our photo of a traditional round Honeywell (R) round room thermostat.

Heating thermostats: Here we use a traditional, and very simple dial-type round wall-mounted thermostat as an example. Notice that the thermostat face has two temperature scales and two pointers.

The top scale on the thermostat and the red arrow shows the "set" temperature that the thermostat is asking for.

The bottom scale shows the actual room temperature.

Rotating the thermostat dial to the right (clockwise) will increase the "set" temperature. Rotating the dial to the left will decrease the "set" temperature.

Heating thermostats are a simple switch to turn on a heating furnace, boiler, or other heat source. As we explain again below about cooling, for a heating thermostat to actually cause the heating system to turn on, the ambient temperature at the thermostat must be below the set point or temperature to which the thermostat has been set.

Make sure that your thermostat has been set to the proper position for the season: cooling or heating. The air conditioner will not run with the switch set to "heating" and conversely the heating system won't run if the thermostat has been set to "cooling."

An air conditioning system thermostat is a switch to turn on or off the A/C equipment as indoor air temperature varies around the thermostat's set point. Air conditioning thermostats are typically wall mounted in the living area. The thermostat, if it's a combination unit, may have both a temperature setting switch and a switch that can be moved from "cool" to "off", or "heat" positions.

For the thermostat to call for cooling it must be in the "cool" position and the temperature set to a level below the ambient air temperature at the thermostat location. Thermostats contain an internal temperature sensor which compares the air temperature at the thermostat to the temperature called-for by the user, turning the cooling (or heating) equipment on or off as appropriate.

What is the setting on this thermostat: precision of room wall thermostat settings, dials, readings

Wall thermostat setting accuracy (C) InspectApedia & KP

What is this thermostat set to? I would say about 66, but the website I got it from said 68? Which is most accurate? Thank you. - K.P. 2/27/2013


KP: you sent us a "stock photo" of a room thermostat, so we don't know if the thermostat in this image is what is actually installed on your wall. We re-drew parts of the image for clarity and added explanatory arrows and have these comments:

The blue arrow is pointing to the thermostat's reading of the current room temperature and is just past 65F - probably around 66 or at most 67F as it's less than half way to the 70.

The red arrow is pointing to the set temperature on the thermostat - the temperature that the building occupant is asking for is set by moving a lever on the right side of the thermostat (the orange arrow) and the "set temperature" being called for is visible by that horizontal red line in the vertical scale on the right portion of the thermostat. The image shows the red line just about exactly between 65F and 70F - or about 67-68 °F.

In sum, in this sketch the thermostat is set to call for heat up to 67F. and the room temperature is reading as just a degree or two below that.

Watch out: the wall thermostat is not a lab-grade absolutely precise instrument in setting nor is it precisely accurate in reading, and even if it were, it would only be reading the temperature right there at the thermostat, not at other places in the room. It would be unreasonable to expect precise, to the millimeter, agreement between the room temperature read-out on the round dial and the room temperature setting on the vertical scale.

How a Digital Room Thermostat Works

Reader Question: Why Does the Thermostat Display Jump Back to 83 After I set It to 68 Degrees?

Honeywell digital room thermostat (C) Daniel Friedman

My daughter had a thermostat replaced about 2 months ago [Trane unit] replaced with Honeywell digital thermo worked well.

Today she called me and said that the thermostat is saying 83 degrees and when she sets it to 72 degrees it jumps back to 83 degrees/she says the thermo is set on the cool side.

Do you know what the problem may be. Please advise - Thank you John

Reply: How a Single-Display Digital Room Thermostat Works

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with air conditioning systems and controls, possibly including something you were not considering. That said, there may not be any thermostat problem in the case you describe. At least not with the thermostat itself.

Our first photograph (above left) shows a basic Honeywell digital room thermostat. This one happens to be set in Heating mode but the principle of how the display works is the same in both heating and cooling modes. You'll see that the display shows the time (12:15 pm) and the current room temperature (67 °F - the house was already cool).

In normal operating mode a digital thermostat whose indicator window shows only a single temperature number displays the current room temperature that it is sensing.

Honeywell digital room thermostat (C) Daniel Friedman

When you press the temperature "set" buttons to call for a decrease in room temperature, (say for air conditioning) or an increase in room temperature (say when in heating mode), the thermostat temperature display temporarily changes to show the "set" temperature - the temperature you are calling for.

When you stop pressing the temperature "set" buttons the thermostat display returns to showing the current room temperature.

Our second digital room thermostat photo (left) shows me pressing the "set down" button until the display shows 54 °F.

This is the new "set" temperature or the temperature I am calling for at the thermostat.

Honeywell digital room thermostat (C) Daniel Friedman

Our third Honeywell digital room thermostat photo (left) shows that a moment after I removed my thumb from the "set" button the thermostat display returned to showing the current actual room temperature (67 °F).

So if the current room temperature for your daughter was actually 83 °F (or in my case 67 °F), that is the number that will show both before and after pressing the "set" buttons.

Only while the set buttons are being pressed will the display show a different temperature (the temperature you are calling for).

As the A/C turns on and begins to lower the room temperature you should see the displayed room temp number gradually drop until it reaches the set temp.

It's possible that your daughter's thermostat is therefore working normally but she simply didn't previously notice how it's display behaves. Often when we notice something for the first time we think there has been a change even if that is not the case.

Two exceptions to this description of how the display on a digital thermostat works

First: if the A/C or heating system is not working properly then even after changing the "set" temperature on the thermostat nothing will happen, or the system may run but never reach the set temperature.

Second: some digital thermostat models show not just one, but two temperatures in the display. One of these is the "set" temperature and the second is the "current" or "actual" temperature. If your daughter's display is one of this type, then it may not be working properly. But from your description it sounds as if she's got a single-display model.

Watch out: if your heating system electrical power has been shut off, when power is restored the thermostat might have "forgotten" the program that you had set into it and you'll need to re-program the device by setting the correct time and then the desired room temperature set back time, and temperature.

Heating & Cooling Control Thermostat Troubleshooting Guide

We have moved and expanded this discussion to a separate article found at THERMOSTAT DIAGNOSTIC GUIDE


Continue reading at THERMOSTAT SETBACK ADVICE or select a topic from the More Reading links or topic ARTICLE INDEX shown below.


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THERMOSTAT SETTING INSTRUCTIONS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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