Furnace Takes Too Long to Heat The Home

The air traveling through the pressure switch hose will put a negative pressure or vacuum on the switch, causing it to close when the burner has sufficient airflow and allowing the ignition process to continue. If the hose has a hole in it, or is not securely fastened to the switch, the pressure switch may only close intermittently, resulting in the furnace taking too long to heat the home. Inspect the pressure switch hose for any damage and replace if necessary.

The air traveling through the pressure switch tube will put a negative pressure or vacuum on the switch, causing it to close when the burner has sufficient airflow and allowing the ignition process to continue. If the tube has a hole in it, or is not securely fastened to the switch, the pressure switch may only close intermittently, resulting in the furnace taking too long to heat the home. Inspect the pressure switch tube for any damage and replace if necessary.

Check the gas control valve to ensure that it is turned on and there is gas present at the valve. Natural gas pressure should be close to 4 inches water column at the furnace input; propane pressure close to 11 inches water column at the furnace input. The gas pressure can be checked with a manometer at the valve. Low gas pressure can cause a weak flames and inconsistant lighting.

The draft inducer motor draws air into the heat exchanger and then exhausts it out the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper air flow. If the draft inducer motor is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the furnace to shut off after a few minutes. If the ignition process stalls, the furnace will shut off and take too long to heat the home. If the draft inducer motor is at fault, replace it.

The draft inducer motor assembly draws air into the heat exchanger and then exhausts it out the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper air flow. If the draft inducer motor is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the furnace to shut off after a few minutes. If the ignition process stalls, the furnace will shut off and take too long to heat the home. If the draft inducer motor assembly is at fault, replace it.

The flame sensor monitors the burner to detect whether or not a flame is present. If the flame sensor is defective, it might fail to detect a flame. If the flame sensor does not detect a flame, the control board will shut off voltage to the gas valve resulting in the furnace taking too long to heat the home. Sometimes, if the flame sensor is dirty, it will fail to detect a flame. Try cleaning the flame sensor with a fine abrasive pad. If the burners still won't stay lit, replace the flame sensor.

The igniter gets very hot and glows bright orange to light the gas burner. If the igniter fails, the gas won't continue to be ignited and the furnace may take too long to heat the home. To determine if the igniter is faulty, remove the igniter and inspect it for cracks. If the igniter is cracked, replace it. If the igniter is not cracked, use a multimeter to test the igniter for continuity. If the igniter does not have continuity, replace it.

The furnace has two seperate requirements for air flow. The homes air is heated and recirculated through the heat exchanger and heat ducts through an air filter. A clogged air filter can cause the furnace to overheat and shut down, and should be replaced at least twice a year depending on the type of filter and environment. The furnace must also have proper airflow through the burner and heat exchanger in order to continue running. The furnace draws air from the surrounding area or from outside the room. If the furnace is located in a utility closet or in a cramped storage room, there may not be sufficient available air for the furnace to heat properly. If the furnace draws air from outside the home, check for an obstructions at the air inlet.

The furnace air filter should be checked and replaced at least twice a year, more often in dusty/dirty environments. A clogged air filter will greatly reduce the air flow of the furnace which can result in the unit taking too long to heat the home.