Thermostats

By Frank G. Ross

A thermostat is a device for controlling a home’s heating and cooling systems so that the temperature in the home is maintained at or near a set temperature.  The unit does this by sensing the room temperature, and when the room temperature varies from the setting on the thermostat, the heating or cooling system is activated.  A thermostat is essentially a heat-activated switch.

While some thermostats control only a heating system, others have a switch that allows a homeowner to change the system from heating to cooling and to operate the fan separately.  Some thermostats also allow the heating and cooling systems to be turned off.

With a dual control thermostat, once the unit is set to either HEAT or COOL, the thermostat temperature setting automatically controls the system by sensing the room temperature and activating the system as needed.

The FAN switch on the thermostat gives a homeowner the option of operating the fan without operating the heating or cooling system.  Operating only the fan causes air to circulate throughout the home.  AUTO is the setting normally used.  In this setting the fan automatically cycles on and off as needed by the heating and cooling systems.

Typically a whole house heating or cooling system is either fully on or fully off.  There is no way to vary the temperature from room to room.  (Some homes do have more complicated systems capable of varying the heating or cooling of individual rooms, called “zones”, but these are the exception.)  When the thermostat calls for heat, the furnace turns on at full capacity.  When the thermostat senses that the desired temperature has been reached then the furnace turns off.  Turning the thermostat higher will not heat a room, or the whole house, any faster.  Similarly, turning the thermostat setting lower will not cause the air conditioning system to cool a room faster.  It just causes the system to run longer to reach the set temperature.

Electronic or programmable thermostats automatically adjust the temperature settings of the thermostat according to a schedule that the homeowner specifies.   These can help save energy costs by allowing the temperature to be lower in winter or higher in summer when a home’s occupants are away or sleeping.

Thermostats are very sensitive and if they are not properly installed they won’t operate as desired.  Anticipator settings on the thermostat match its operation to the furnace.  If set improperly the furnace may cycle off and on too frequently or an incorrect setting may allow the room temperature to drop too low or rise too high before the furnace comes on or goes off.  In addition, the thermostat should be level, out of direct sunlight, and away from other heat sources.

When a problem arises with a thermostat and adjusting the settings correctly doesn’t solve it, consider replacement rather than repair.  If you need to replace a mechanical thermostat, think about replacing it with a programmable electronic thermostat to enable your heating and cooling system to work more efficiently.

Frank Ross is a Certified Utah Home Inspector for Pillar to Post Professional Home Inspection and a full member of the National Association of Certified Home Inspectors and a member in good standing with the Utah Better Business Bureau.  Readers may contact Mr. Ross at (435) 867-6400 or frank.ross@pillartopost.com or www.pillarposthomeinspection.com