Thermostats are devices designed to control the heating and cooling systems in a building so that air temperature remains comfortable. According to InterNACHI’s Standards of Practice, inspectors are not required to verify, inspect or determine thermostat calibration, heat anticipation, automatic setbacks, timers, programs or clocks. It is wise, however, for inspectors to understand thermostat operation and solutions to common defects.
Thermostats can be manually controlled or set to activate automatically based on timers or room temperature readings. Most thermostats contain two meters: the “set” temperature that the thermostat is asking for, and the actual temperature. On a traditional dial-type thermostat, the user can increase the set temperature by rotating the dial clockwise, and lower it by rotating it counter-clockwise. Newer thermostats usually have digital displays, which can be used to adjust automated heating and cooling schedules.
In order to avoid false or "ghost" readings, which will cause unnecessary furnace or air-conditioner cycling, the thermostat must be installed so that it correctly reads the room temperature. The following locations may cause the thermostat to give false readings:
near a heat source, such as a fireplace, hot water pipes, bright lights, direct sunlight, electrical appliances that produce heat;
in a drafty hallway, or near a window or exterior door that is opened often; and
on an outside wall. Outside walls are too affected by outside temperatures, which may make the thermostat "think" the air in the house is warmer or cooler than it really is.
Common Thermostat Problems and Solutions
erratic operation or fluctuating temperature. This is often caused by poor pin connections between the thermostat and the backplate when the backplate is flexed against an uneven wall. To allow the backplate to flatten out, loosen the screws that attach the backplate to the wall, then snap the thermostat back onto the backplate.
a thermostat that doesn’t respond to changes in room temperature. This can happen when there is air passing over the temperature sensor from a hole in the wall behind the thermostat, through which wires enter from the air-handling unit. To rectify this, insulate the hole behind the thermostat with insulation, spray foam, or any other insulating material.
temperature that is inaccurate. A convenient way to test the temperature sensor is to tape a thermometer to the wall next to the thermostat and wait 15 minutes. A faulty thermometer needs to be recalibrated. Instructions for recalibration vary by manufacturer.
loss of power. This may be caused by the following two situations:
If the air handler powers the thermostat, check the circuit breaker meant for the air handler and make sure it has not tripped.
If batteries power the thermostat, make sure they are lithium, not alkaline. Alkaline batteries will die rapidly or cause erratic thermostat operation.
Maintenance and Other Tips
Give the thermostat's interior a light dusting with a small, soft paintbrush. Canned air can also be used to blow off dust. Twist the screws to remove the cover. Be sure to clean the contacts, which are small metal plates within the unit. The wires coming from the transformer attach to the contacts. Do not touch any of the interior parts with fingers.
If the base is loose, re-tighten the screws. Check the wires coming from the transformer. If any corrosion is present, remove the wire from the contact and clean it. Use a wire stripper to remove the surrounding insulation, cut back the wire, and reconnect it.
Make sure the terminal screws are tight.
For wireless thermostats, make sure the model number of the thermostat matches the model number of the receiver. If the model numbers do not match, the stat and receiver will not be compatible.
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."
Thermostats that contain a mercury switch must remain perfectly level or they may not control the temperature setting.
A Few Notes on Energy Savings
Many people believe that furnaces work harder than normal to warm an area back up to a comfortable temperature, which will counteract energy savings gained from turning the thermostat down. This belief is a misconception that has been disproved by years of studies and research. Fuel is saved between the time the temperature is stabilized at the lower level and the next time heat is needed, while the fuel required to re-heat the space is roughly equal to the fuel saved while the building drops to a lower temperature.
According to the U.S. Department of Energy, consumers can save 10% on their utility bills by setting their thermostat back 10° to 15° for eight hours. This can be accomplished easily with a programmable thermostat.
Be careful not to set the thermostat so low in the winter that pipes freeze, or so low during the summer which may allow humidity-spawned mold to grow.
In summary, thermostats are used to ensure the comfort of building occupants through the proper control of the heating and cooling cycles.
by Nick Gromicko, CMI®
Courtesy of InterNachi