A furnace turns on when the room temperature falls below the thermostat’s set temperature. In a gas or oil furnace, the burner ignites and heats the air; in an electric furnace, heating elements increase the air temperature. A blower sends hot air from either type of furnace through ducts into the room. Without an anticipator setting, a furnace would continue to heat the air after the room has reached the desired temperature, or fail to start when the temperature falls.
Located behind the thermostat cover, the heat anticipator has a floating arm with a triangle-shaped pointer. Through an opening in the pointer you can read amperage settings on an engraved scale; you may notice the word “longer” on the scale. Scale settings typically range from 0.1 to 2 amps. A sliding adjustment lever, which makes it possible to change the setting, attaches to the pointer. The anticipator also contains a heating coil and a metallic spring heat sensor.
The proper anticipator setting will turn off the furnace blower as soon as the entire room reaches the set temperature. The heating coil warms the heat sensor to the set temperature, and the thermostat stops calling for heat just before the room is sufficiently heated. The furnace blows any remaining warm air, but no longer actively warms the air. The anticipator ensures that the room temperature will not exceed or fall short of the set temperature. Inspectapedia recommends setting the anticipator to the furnace manufacturer’s preferred setting; if you do not have this information, use the anticipator manufacturer’s setting.
The anticipator controls the length of time that passes before a furnace turns on or off. If the furnace continuously and rapidly switches on and off, you can move the triangular pointer to a lower number or one notch closer to the word “longer.” Move the pointer to a higher number or one notch away from “longer” to prevent the furnace from remaining on or off too long. A furnace must run for two or three hours and for several cycles before a new anticipator setting will stabilize.
For accurate results, the anticipator’s current and voltage must match those of the furnace. A professional heating technician can check and adjust this setting for you. If furnace performance does not stabilize after you adjust the anticipator’s ampere setting or the furnace’s current and voltage, you may need to install a new thermostat. If you have a mechanical thermostat with a mercury vial, the anticipator will not work properly unless the thermostat is level.
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