Disclosed is a gas furnace for indoor heating. The gas furnace includes a burner to generate high-temperature exhaust gas, an exhaust flow path, a blower to suction indoor air through a recovery flow path, a supply flow path to guide the indoor air to the indoor space after undergoing heat exchange in the exhaust flow path, and a fuel supply unit including a fuel supply line and a fuel discharge line, configured to supply fuel to the burner, and a valve between the fuel supply line and the fuel discharge line. The valve includes a step motor, and a blocking member coupled to a rotating shaft of the step motor and configured to move straight via by driving of the step motor, and an opening degree of the valve between the fuel supply line and the fuel discharge line is adjusted by the straight movement of the blocking member.

A method of generating a control signal for a temperature control system is disclosed. The control signal has one of an on state in which the temperature control system is to be activated and an off state in which the temperature control system is to be deactivated. The method comprises calculating a temperature error measure in dependence on a target temperature and a current temperature value. A rate of temperature change in the environment is determined and used to set a variable error threshold. The method switches between a continuous on signal mode and a pulse-width-modulation (PWM) mode, in which the output signal comprises alternating off and on periods in accordance with a PWM pattern. The switch occurs in dependence on the temperature error measure and the variable error threshold.

A combination boiler provides heated water to a boiler loop and heated domestic hot water (DHW) to a DHW loop. A primary heat exchanger is connected to the boiler loop. A burner provides heat to the primary heat exchanger and an input fan supplies a fuel and air mixture to the burner. A secondary heat exchanger transfers heat energy from the boiler loop to a domestic water loop. A controller determines a boiler loop flow rate. The controller measures an input temperature of the boiler loop, an output temperature of the boiler loop, and a DHW output temperature of the domestic water loop. The controller determines a DHW input temperature and estimates a DHW flow rate. The input fan speed is initiated or operated according to a required heat output of the burner corresponding to the DHW flow rate.

Disclosed is a gas furnace for indoor heating. The gas furnace includes a burner to generate high-temperature exhaust gas, an exhaust flow path, a blower to suction indoor air through a recovery flow path, a supply flow path to guide the indoor air to the indoor space after undergoing heat exchange in the exhaust flow path, and a fuel supply unit including a fuel supply line and a fuel discharge line, configured to supply fuel to the burner, and a valve between the fuel supply line and the fuel discharge line. The valve includes a step motor, and a blocking member coupled to a rotating shaft of the step motor and configured to move straight via by driving of the step motor, and an opening degree of the valve between the fuel supply line and the fuel discharge line is adjusted by the straight movement of the blocking member.