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Excess air control

  • US 4,703,747 A
  • Filed: 09/17/1986
  • Issued: 11/03/1987
  • Est. Priority Date: 09/17/1986
  • Status: Expired due to Term
First Claim
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1. In a gas furnace of the type having a heat exchanger and a variable speed inducer motor, an improved method establishing a desired level of excess air comprising the steps of:

  • using empirical data obtained from a gas furnace operating under selective variable conditions, establishing a calibration factor for obtaining a desired excess air level for a furnace of nominal design characteristics;

    providing a pressure switch that is responsive to a selected pressure drop level in the heat exchanger, said pressure drop level being selected so as to be commensurate with a theoretically desired excess air level under firing operating conditions;

    accelerating the variable speed inducer motor until said pressure switch closes and recording the motor speed at that time; and

    applying said calibration factor to said recorded motor speed to obtain a desired induced motor speed.

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