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Fan Controls
In order to turn on the fan only when it is needed, we have various means of controlling it.
Early furnaces used heat operated controls that sensed the increased heat inside the furnace to tell the fan when to come on. These controls were used on both oil and gas fired furnaces.
Below is a video about one type of heat operated control.
Early furnaces used heat operated controls that sensed the increased heat inside the furnace to tell the fan when to come on. These controls were used on both oil and gas fired furnaces.
Below is a video about one type of heat operated control.
When installing the fan switch, there is a sensor or probe that is placed near the heat exchanger, so it can sense the heat exchanger temperature. The video below demonstrates how the above fan switch accomplishes this.
These controls are adjustable for their fan on and fan off temperatures. They also usually incorporated a high temperature limit to shut off the heat source if the temperature inside the furnace reached a dangerous level.
This setting is sometimes adjustable but usually cannot be raised above 200 degrees F. The video below covers how to set the temperatures so that the fan will come on when the heat exchanger is warm. After the burner has shut down, the fan will continue to run until the heat exchanger has cooled.
This setting is sometimes adjustable but usually cannot be raised above 200 degrees F. The video below covers how to set the temperatures so that the fan will come on when the heat exchanger is warm. After the burner has shut down, the fan will continue to run until the heat exchanger has cooled.
During the 1980s, electronic timers began to be used to control fan on and off times. The had field adjustable on and off times to adapt the timing to the individual unit. These controls had no sensor for temperature.
These units must be used with a separate high temperature limit that senses temperature near the heat exchanger.
The video below explains how these controls work.
These units must be used with a separate high temperature limit that senses temperature near the heat exchanger.
The video below explains how these controls work.
More coming