Control method of gas furnace

1. A method for controlling a gas furnace that performs heating operation, the method comprising:

receiving a first heating signal;

calculating a certain heating capacity smaller than a maximum heating capacity of the gas furnace, according to the first heating signal; and

operating a heating of the gas furnace with the calculated certain heating capacity, wherein the calculating of the certain heating capacity comprises calculating the certain heating capacity according to a difference between an intake air temperature sucked into the gas furnace and a reference temperature, wherein the intake air temperature is variable over time, wherein the reference temperature is set to a specific temperature higher than a specific intake air temperature at a certain time point among the variable intake air temperature, and wherein the certain heating capacity is varied in a stepwise manner according to a magnitude of a temperature difference obtained by subtracting the intake air temperature from the reference temperature, based on a preset starting capacity.

2. The method of claim 1 , wherein the reference temperature is set to a temperature higher than the intake air temperature by 0.5 to 2.5° F. at the certain time point.

3. The method of claim 1 , wherein the step (c) calculating of the certain heating capacity further comprises:

determining whether the gas furnace is in operation according to a previous signal;

determining whether the previous signal is the first heating signal or a second heating signal which causes an operation of the gas furnace at the maximum heating capacity, when the gas furnace is in operation;

calculating the certain heating capacity according to a difference between the intake air temperature and the reference temperature, wherein the reference temperature becomes a reference temperature in the previous signal, when the previous signal is the weak first heating signal; and

calculating the certain heating capacity according to the difference between the intake air temperature and the reference temperature, wherein the reference temperature is set based on the intake air temperature at a time point of signal change, when the previous signal is the second heating signal.

4. The method of claim 3 , wherein the step (c) calculating of the certain heating capacity further comprises:

sucking air into the gas furnace for a certain time, if the gas furnace is not in operation; and

calculating the certain heating capacity according to the difference between the intake air temperature and the reference temperature, wherein the reference temperature is set based on the intake air temperature after the certain time.

5. The method of claim 4 , wherein sucking air into the gas furnace is maintained for 15 to 45 seconds using a blower provided in the gas furnace.

6. The method of claim 1 , wherein the certain heating capacity is maintained to be identical with the starting capacity, when the temperature difference is within a first reference range.

7. The method of claim 6 , wherein the certain heating capacity is increased by a certain ratio from the starting capacity when the temperature difference is within a second reference range which is larger than the first reference range.

8. The method of claim 6 , wherein the certain heating capacity is reduced by a certain ratio from the starting capacity when the temperature difference is within a third reference range which is smaller than the first reference range.

9. The method of claim 1 , further comprising

storing the reference temperature, wherein the calculating of the certain heating capacity comprises calculating the certain heating capacity based on the stored reference temperature.

10. The method of claim 1 , further comprising

receiving a second heating signal which causes an operation of the gas furnace at the maximum heating capacity; and

operating a heating of the gas furnace at the maximum heating capacity of the gas furnace, according to the second heating signal.