Control method of gas furnace

A method for controlling a gas furnace, the method comprising:

• measuring an indoor temperature;
• comparing the indoor temperature with a set temperature for heating;
• and
• operating the gas furnace in a first heating with a predetermined heating capacity, which is lower than a maximum heating capacity of the gas furnace, when the set temperature for heating is higher than the indoor temperature by a temperature value which is less than a predetermined temperature value, wherein the predetermined heating capacity for the first heating is maintained at a current heating capacity for the first heating, when the gas furnace operates in the first heating, and when an operating duration with the current heating capacity for the first heating is less than a first time value, wherein the predetermined heating capacity for the first heating is increased in value by a first capacity value from the current heating capacity for the first heating, when the gas furnace operates in the first heating, and when an operating duration with the current heating capacity for the first heating is greater than the first time value, wherein the current heating capacity is the heating capacity at which the gas furnace is currently operating, and wherein the first capacity value before a direction of increase or decrease of the predetermined heating capacity is changed is greater than the first capacity value after the direction of increase or decrease of the predetermined heating capacity is changed.