Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR HANDLER / BLOWER UNITS
AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE
BACKDRAFTING HEATING EQUIPMENT
BACKUP HEAT for HEAT PUMPS
BLOWER FAN OPERATION & TESTING
BOOKSTORE - InspectAPedia
CIRCULATOR PUMPS & RELAYS
CONVECTOR HEATERS - HYDRONIC COILS
COOL OFF HEAT, Thermostat Switch
DEFINITION of HEATING & COOLING TERMS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCT SYSTEM & DUCT DEFECTS
ELECTRIC MOTOR OVERLOAD RESET SWITCH
ELECTRICAL POWER SWITCH FOR HEAT
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON Thermostat Switch
FAN, COMPRESSOR/CONDENSER UNIT
FAN CONVECTOR HEATERS - HYDRONIC COILS
FAN LIMIT SWITCH
FLOODED HEATING EQUIPMENT REPAIR
HEATING LOSS DIAGNOSIS-BOILERS
HEATING LOSS DIAGNOSIS-FURNACES
HEATING SYSTEM INSPECT DIAGNOSE REPAIR
LOW VOLTAGE BUILDING WIRING
LOW VOLTAGE TRANSFORMER TEST
MANUALS & PARTS GUIDES - HVAC
NO HEAT - BOILER
NO HEAT - FURNACE
ODORS FROM HEATING SYSTEMS
OIL FILTERS on HEATING EQUIPMENT
PULSE COMBUSTION HEATERS
Reset Switch - Heater Primary Control
Reset Switch Broken - Quick Repair
RESET SWITCH - ELECTRIC MOTOR
Reset Switch - Stack Relays
STEAM HEATING SYSTEMS
THERMOSTATS, HEATING / COOLING
THERMOSTATS, WATER HEATER
THERMOSTATIC EXPANSION VALVES
ZONE VALVES, HEATING
Heating & Cooling Thermostats, how to install, set, troubleshoot & repair home page: this article series explains selection, installation, use, setting, and adjustment of heating or cooling system room thermostats or "wall thermostats".
Here in the article links found at Related Topics and at the top of this article we provide a complete guide to buying, installing, using, adjusting, & repairing thermostats for heating or air conditioning or heat pump systems. This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. Our page top photograph illustrates an antique room thermostat still in use at the FDR Estate in Hyde Park, NY.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
If your heating system is not working at all, start at HEAT WON'T TURN ON.
Article Series Contents:
Heating & Air Conditioning Thermostats where are thermostats usually located, what types of thermostatic controls are used on various heating and cooling systems, how do we find all of the thermostats, how do we set, adjust, and use thermostats
The round Honeywell (R) wall thermostat shown in this photo has been locked in a plastic enclosure to prevent people from changing its set temperature. Set temperature and how the thermostat works are described in excruciating detail below.
At HEAT ANTICIPATOR Adjustment we describe how an internal adjustment can be made to this thermostat to improve its operation in some types of heating systems. Also see THERMOSTAT CALIBRATION where we discuss the accuracy and calibration of room thermostats.
Room thermostats for air conditioning work and are set the same as when these devices are used for controlling heating systems. We provide lots of detail about how these devices work - see THERMOSTAT SETTING INSTRUCTIONS below.
On this wall thermostat the red pointer shows the current room temperature.
The black pointer at the center of the scale at the bottom of the little window shows the temperature that the thermostat has been "set" to.
The "Set Temperature" is the temperature that the room occupant is requesting.
Moving the thermostat adjustment lever (located at the top, side, or bottom of the thermostat depending on the model) will change the set temperature up or down, causing the heating or air conditioning system to turn on or off as needed.
See Detailed Guide to Room Thermostats below.
Typically the display changes in response to pushing the thermostat control buttons.
Most digital room thermostats are "programmable" - you can set the thermostat to set back the room temperature at night (in heating mode, for example) and many models allow different time and temperature settings both throughout the day and for individual days of the week as well.
Our digital thermostat shown at left indicates the time (5:43 PM) in the left side of the display and the current temperature (53 °F) in the right side of the display.
With the thermostat's plastic cover "shut" it's operation is very simple, just showing up and down arrows that temporarily call for a higher or lower room "set" or "desired" temperature.
We opened the plastic thermostat cover to show additional detailed controls and instructions.
Our Favorite Room Thermostat - The Honeywell RTH2300 / RTH221
The Honeywell RTH2300 / RTH221 series room thermostats are easy to program, permit different weekday and weekend programs, and include a "hold" button that is invaluable for keeping the thermostat at a fixed setting without losing the whole program.
Honeywell displays a "Rated Overall Best Brand" sticker on the packaging indicating that this model received a "Best" rating by an independent Frost & Sullivan study.
At THERMOSTAT SWITCHES, INTERNAL we describe how to set this thermostat's internal "Gas" or "Oil" slide switch.
We describe the operation of a typical digital room thermostat for heating or air conditioning later in this article at DIGITAL ROOM THERMOSTAT OPERATION
A simpler programmable Honeywell® digital room thermostat is show in our photo at left. This is a Honeywell CT2700 Electronic Round Programmable Thermostat.
The thermostat is showing the current time (12:15 PM) and current room temperature (67 °F).
This unit does not provide additional buttons under a cover. But by pressing the center "Set" button the display changes to allow the user to set a desired time and temperature setting for day and night time temperatures.
At THERMOSTAT SWITCHES, INTERNAL we discuss setting the thermostat's internal F/E toggle switch.
Watch out: we installed and tested two of these thermostats over several years of use. While the device is simple, un intimidating, and easy to program, the lack of a "hold" feature was annoying and required more fooling around; we also would have liked an additional daytime automatic setback period that this device doesn't offer.
But the worst discovery was that our oil burner was short cycling, sometimes turning on for just a few seconds - a problem that we finally traced to a defect in one of these thermostats. (The problem ceased when we swapped in our preferred thermostat shown above). We also found the flat cable wiring of this thermostat very fragile - eventually the display cable simply detached itself from its contacts.
The Nest™ Learning Thermostat - home automation features include buiding occupancy monitoring & communicating with the Nest Protect Carbon Monoxide & Smoke Detector
Photo at left: the Nest® Learning Thermostat on demonstration display at a Home Depot store in 2013. [Click to enlarge any image]
Adapting data from the company's website:
The Nest® Learning Thermostat also communicates wirelessly with Nest's Protect® shown at left, the company's carbon monoxide detector & smoke detector released in 2013 (CO DETECTION OPTIONS).
Really?: this smart thermostat is very appealing but in our OPINION it is a bit pricey at $250./ per thermostat plus $119 for concierge installation of one unit, more-so in buildings with multiple heating zones each of which requires control by an additional individual thermostat. The good news is that most consumers probably don't need to hire a concierge service to install the unit.
There is no question that the Nest® learning thermostat is a beautiful and clever product. We considered buying the three Nest thermostsats that would be required to test and review the product and to try controlling our three heating zoned building temperature by cellphone from another country.
But needing three thermostats for the test building we felt that the more than $1100. price was a stumbling block. In our OPINION the promise of a 20% reduction in heating costs is probably an up-to number that will only be reached if you are not already using a programmable room thermostat that permits night and weekend temperature setbacks.
The legal definition of up to in advertising law states roughly that 10% of any product or product installation (not just this one) using the term up to in advertising should meet the up to claim.
If however you want to use building temperature sensing or time of day to automagically control additional building components such as programmable LED lighting, the value of the Nest® is increased accordingly. See LED BULB & LIGHTING TYPES for notes on programmable or controllable LED lights in buildings.
Automatic radiator/baseboard valves provide thermostatic controls that can be installed on individual hot water radiators, steam radiators, or heating baseboards. The automatic radiator or baseboard valve will automagically open or close to attempt to control room temperature to the desired level.
Shown at left is an adjustable individual thermostatic control installed on a hot water radiator in Molde, Norway.
For details see RADIATOR VALVES & HEAT CONTROLS This article describes these automatic or thermostatically controlled radiator valves (such as the Armstrong RV-4) that will allow you to set the desired room temperature.
Also see RADIATOR STEAM VENTS, 1-PIPE SYSTEMS for a description of automatic steam vents used to control the rate at which steam heat radiators will get hot. Automatic steam vents can help balance the delivery of otherwise uneven steam heat throughout a building.
Remote control thermostats such as the unit shown at left are usually used with air conditioning or heating split systems using an outside compressor/condenser unit and one or more indoor wall-mounted cooling or heating units..
The thermostat controls in the hand-held remote control communicates with a wall-mounted air conditioner or heater using infra red signals.
The open finned area at the bottom of this Sanyo control (at the left in our photo) permits ambient air to enter the control for purpose of sensing the air temperature.
A control such as this Sanyo™ unit can be quite sophisticated and include automatic set back temperatures, timers, etc.
See SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS for details, including troubleshooting and fixing remote control thermostats themselves as we describe in detail at SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS-FAQs
Hand held A/C remote control does not seem to be working
Have a hand held remote for TCL air-conditioner (split model TAC-30CHS/G). when we set temperature, conditioner blinks what you want it to be, then it goes to inside temperature (suppose to do this) but then it quickly jumps to 34 degrees & switches off. Guessing it is thermostat? Anne Webber 9/2/11
Anne, sounds odd to me too. Try
Outdoor Thermostats on the Heat Pump Compressor-Condenser Unit
Heat Pump Outdoor Thermostats are used to control the turning on and off of backup heat.
Our photo (left, courtesy of Neal Renn shows the thermostatic control unit in the outdoor compressor/condenser unit of a residential heat pump.
See Heat Pump Thermostats - Outdoors and BACKUP HEAT for HEAT PUMPS and also see Detailed Case of a Heat Pump that Put out Heat when Cooling was Required
Choices of Room Thermostat Models, Brands, Features
In the article above and at Related Links (near page top) we describe the installation and use of most types of room thermostats used for heating, cooling, even dehumidification in buildings. But there are hundreds of models and features available. The largest selection of room thermostats we find anywhere is at Grainger who has over 250 models in their online catalog. http://www.grainger.com - but beware not every thermostat description necessarily names all features.
Bimetallic Element thermostats use a bimetallic spring consisting of strips of two different metals fused together, typically into a coil shape. As room air temperature causes the two metals to expand or contract at different rates, the effect is that the spring coils up or un-coils, moving a switch that turns heating or cooling or or off.
Bellows Element thermostats are filled with a volatile liquid that vaporizes at temperatures typically found indoors. As the liquid vaporizes pressure inside the bellows expands, translating temperature change into the movement of a contact to turn heating or cooling on or off in response to building temperature.
Thermistor-type thermostats use a tiny solid-state electronic component, a type of resistor whose electrical resistance changes in response to temperature. By combining the thermistor with appropriate additional circuits and controls the thermostat uses the change in resistance to control the switching of the thermostat's control of cooling or heating on or off in response to room temperature.
For details: at TEMPERATURE RESPONSE of Room Thermostats we give a detailed description of how room thermostats sense & respond to room temperature, and at HEAT ANTICIPATOR Adjustment and THERMOSTAT SWITCHES, INTERNAL we explain methods used to fine-tune thermostat operation in response to temperature swings, thus adjusting the burner on-cycle or fan operation if the heating system uses a fan.
Also see THERMOSTAT CALIBRATION where we discuss the accuracy and calibration of room thermostats.
Room thermostats used to control steam heat may vary from their cousins illustrated above, or not - depending on just what the thermostat is controlling. In a residential application a standard room thermostat works fine to turn on or off the steam boiler.
But in larger buildings you may find that the room thermostat for steam heat is controlling a valve or relay that admits steam to radiators in one room or in just one section of a building.
In our photo at left, this wall thermostat controls steam heat in a college office in Poughkeepsie, NY.
[Click to enlarge any image]
The upper scale indicates the current room temperature.
The lower dial-scale is the set-temperature adjustment on this thermostat. The thermostat controls a steam radiator valve that in turn admits or shuts off heat into the space managed by this device. RADIATOR & BASEBOARD THERMOSTATS, Automatic - TRVs provide an alternative that can control individual hot water or steam radiators in buildings.
This topic has been moved to its own article now found at THERMOSTAT SET PROCEDURE
Some programmable digital room thermostats include an internal battery that will allow the device to remember the program that you have set even if there has been a power outage. This topic has been moved to its own article at THERMOSTAT BACKUP BATTERIES - for temporary or full time operation.
We have moved and expanded this discussion to a separate article found at THERMOSTAT DIAGNOSTIC GUIDE
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: A/C blower making loud sound - doesn't respond to the thermostat properly
My ac blower was making a loud sound so it went bad i replace it with a new one and know the thermostat is not working properly the setting on the thermostat it works wrong when i set it on the auto and cool it does not turn on the blower when i set it on fan and cool it works but it does not shut off i change the thermostat and it does the same thing. Do you know what it could be? - Angelo 8/5/11
Angelo I'm not sure but most likely there was a wiring change needed, or perhaps someone shorted a control board or relay
Question: A/C freezes up after blower was shut off - compressor doesn't stop
Recently my A/C began to freeze up after the blower was shut off by thermostat at right temp, I noticed that the thermostat would shut off the blower but not the outside unit causing it to keep running and freeze up the inside coils, but when I turn thermostat to "ON" and just let it blow, it keep running and getting too cold. How do I find out what is making the thermostat only control the inside unit. - Kewl Jungles 8/8/11
Question: Inadequate cooling, tech says just keep running the system
We just had evaporator coils replaced on both a/c systems. One system has been cooling fine ever since. The other only seems to cool at night. The thermostat seems to be working OK and the air coming out of the vents is cool although perhaps not quite as cool as that coming out of the vents driven by the other system.
The system that not working correctly gets to be six degrees warmer than the set temperature on the thermostat. The company that installed the new coils came back and just checked pressures at the condenser and said everything seems to be working OK and that it may take some time for the everything to cycle through the new equipment. Any suggestions of problems that may result from new coil installation or what else could be causing the problem? Mike
A/C equipment does not normally need a "break-in" period to begin working properly. In fact about the only thing that leaving the equipment running will accomplish is that it lets the technician get in her truck and get the heck out of there.
An exception might be a response to an owner who complains that the house is too hot or too cold when the system has been just turned on. If the heating system is indeed producing output air at normal heating temperatures or cooling air at normal cooling system output temperatures and air flow rates, then indeed time may be all that's needed to get the building to the desired temperature.
There are a number of explanations for inadequate cooling, including in a new installation (where we figure we don't have blocked air filters etc) improper refrigerant charge, or a refrigerant metering device not working properly. Call the service company and ask for help from a more experienced technician.
Question: My A/C blows warm air for a while before cool air comes out
when I turn the air conditioner onto heat it blows out warm out for a few minutes and then cool air, would this be the thermostat or would it need gassing, it is just over five years old. - Marylin 3/14/12
Marylin, if the air produced by your system is adequately cool after the initial warm air delivery I suspect your building may have poorly insulated ductwork running through a hot attic of some length. The hot duct is warming the initial airflow.
Hi Dan, if it was the ductwork wouldn't it have played up by now i have had the unit for just over five years, when I go downstairs to the main unit and touch the pipe it is hot,but we just cant seem to get enough heat upstairs..
Yes Marylin I agree - that's part of the difficulty of guessing at a question with not much information. However depending on duct type, routing, condition, insulation can fall off, be torn off by animals, or open and leak - it's worth a careful inspection in any case.
Try the search box just below or if you prefer, post a question or a comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.