Gas Furnace Dos and Do Nots
by Guest on May 5, 2012
Gas Furnace Do's
- Change the Air Filter Regularly
- Check the fan belt to proper tension and wear
- Check the fresh air intake grill
- Properly service the furnace before the start of the heating season
- If the spill switch trips do not bypass the safety control correct the venting problem.
- Over tighten the fan belts, the belt should be just tight enough not to slip.
- Adjust the gas regulator pressure setting
- Block off fresh air intake. (If the furnace can't get its own air, it will take yours)
What is Proper Service
Furnace Temperature Rise: Most Residential furnaces are designed to work with a 40°F -60°F Temperature Rise (Supply Air Temperature - Return Air Temperature ), check the nameplate of your furnace for its design temperature.
Stack Temperature: The temperature of the flue 18" from the furnace should be the least 225°F. If it is lower than this then the flue gas will drop below the dew point more it vents from the top of the chimney. This will cause condensation in the chimney. This moisture is very acidic and will quickly damage the chimney.
Gas Manifold Pressure: The pressure on the gas manifold determines how much fuel your furnace will burn. Even a slight change from the design pressure can have a big effect on the performance of the furnace. This should only be tested by a licensed gas fitter, and at the original startup of the furnace. This test can also be done by clocking the gas meter, with only the furnace burners running.
Chimney Draft: The draft up the chimney should be at least -0.02" w.c. with all gas appliances running, all exhaust fans running. And all the windows and doors closed to the house. If the Draft is less than -0.02"w.c. additional Fresh air must be brought into the house. If the draft is greater than -0.05" can reduce the appliance efficiency by allowing the flue gases to pass too quickly through the heat exchanger.
CO Test exhaust: Test the flue gas for Carbon Monoxide. A properly set up burner should produce less than 10 PPM., high efficacy furnace will often produce more. If more than 50 PPM then the burners should be removed, cleaned, and set up, If greater than 300 PPM, repairs must be done ASAP. If higher than 500 PPM the furnace must be shut down until repairs are made.
Visual Inspection of the heat exchanger: Visually check the interior and exterior of the heat exchanger wear possible. Most of the heat exchanger is hidden from view, but the area that can be seen is a good indicator of the rest of the heat exchanger. The older or suspicious heat exchanger can be tested by smoke, or sulfur, or cutting in an inspection door. If the burner is producing CO then testing the supply air for CO can show the presents of a crack.
Visual Inspection of the Vent Connector: Check the connector between the furnace and the chimney. Signs of moisture indicate additional problems, On the signal walled pipe, try squeezing the vent connector to check for interior rusting, weak pipes should be replaced.
Visual Inspection of the Chimney: If your furnace is connected to a Masonry, then it should behave as a metal liner, if not then remove the cleanout to check for debris. Visually inspect the exterior of cracks. Check the interior tile liner, if the liner appears cracked then it must be relined. metal Chimneys are much more reliable, but if moisture can be seen on the vent connector then the metal chimney should be inspected.
Check blower operation. Check the blower for dirt buildup on the fan blades, wear in the blower, and/or motor bearings. Pulley wear and alignment, belt tension, and wear. Lubricate when and where required.
Combustion Fan Motor: Check the combustion fan for signs of rusting on the housing, check them for bearing wear on the motor.
Burner Operations: The furnace on a normal call for heat will start the combustion fan, if present, for 30 seconds before trying to light the pilot or main flame. Spark Ignitors should light the pilot after a few sparks, HSI (Hot Surface Ignitor ) will light the main flame directly, standing pilots will light the main flame. After the burner is lit, then the fan should start. 30 to 90 seconds later. The burner and fan should stay on until the thermostat is satisfied. Once the thermostat is satisfied, the burner should stop, and the fan should run until the furnace is cooled down. Once the fan stops it should stay off until the next call for heat.
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