Patent ID: 6764298
Filing Date: 2004-07-20
Classification: F23D,F23N

Abstract:
A method for controlling an air fuel ratio in a gas furnace, comprising:determining a rotational speed of a fan motor of the furnace; detecting a variation in a heat output rate of the furnace based on a pulse width modulation count value; detecting a variation in air flow rate based on a variation in the rotational speed of the fan motor; detecting a variation in the pulse width modulation count value based on the variation in the rotational speed of the fan motor; determining a relational expression between the rotational speed of the fan motor and the pulse width modulation count value based on the variation in the pulse width modulation count value; applying the detected rotational speed of the fan motor to the relational expression until the heat output rate reaches a preset heat output rate; and controlling operation of a gas valve of the furnace based on the pulse width modulation count value.