One of the home appliances that need to be regularly maintained and tuned for optimum performance is the central heating system or also known as a furnace. It is important especially during winter and colder times and while you can always hire people to do it for you, getting your hands dirty in order to learn the trade yourself can be worth the time as well. Furnace cleaning is easy to understand, albeit being a bit complicated in its mechanism. Doing it yourself will let you save up on cash as well as the ability to save your household from the troublesome cold.
The furnace technology of today does not allow for simple and swift furnace cleaning, as the appliances used nowadays are stronger and higher in efficiency. The cleaning procedures are also more precise. Start by checking the igniter with an ohmmeter. The readings should be between 11 and 17 ohms for furnaces with silicon nitride igniters and 50 to 100 ohms for carbide igniters. The igniter should be replaced if the readings are beyond those. Then hook the flame sensor and sensor wire to your multimeter in series before firing the furnace in heat cycle. Certain control systems only need 0.5 uA reading, though most appliances would read 1.5 to 4 uA. If it is below 1 uA then you will have problems.
Next is to pull and clean the burners which may come with slots or ‘wings’ which are aligned to the burners next to it. Check and clean them from debris with a stiff-bristled brush. Blow the burner and its vestibule area with air pressure or dry nitrogen. A dirty burner can produce high carbon monoxide along with delayed ignition. Severely rusted burners should be replaced. Your heat exchanger should not have excessive rust, crack or holes. It is best to inspect furnace cleaning manually, though it requires practice to recognize them. You can also use inspection cameras or dye penetration inspection systems. Make sure the metal flue has no rust or holes and is supported properly.
After this you can check the system static pressure, but you should first determine if your furnace has non-variable speed motor or otherwise. The former system will have a total external static pressure (ESP) of .50-in while variable speed motor systems have .80-in maximum. 80% induced draft furnaces need 130 cfm of supply air per 10,000 Btu and 150 cfm of supply air per 10,000 Btu for 90% furnaces. Set the correct cfm for your furnace by referring to a fan chart. Make sure gas pressure and heat exchanger temperature are set properly.
Then you should analyze your combustion. For proper calibration, start the combustion analyzer outdoors. Record and measure the highest CO level during the first 60 seconds. Natural-draft furnaces should have a CO level of 100 to 400 ppm and 90% condensing furnaces should have 100 to 1,000 ppm. Within three minutes the reading should drop to below 100 ppm. If the CO level slowly rises during run cycles then there is a safety issue and the furnace would require further testing. After your furnace cleaning is complete, you can choose to maximize reliability and efficiency of your furnace by setting the heat-off delay to the longest duration available, which is usually for 180 seconds.