Cleaning and maintaining the furnace is not something that anyone would look forward to, especially if the furnace has not been cleaned for a long time. It is true that it would be a lot easier to just call service technicians who would be doing the same thing you are, but if you do it yourself, you can save up on money and ensure that every little part of your furnace cleaning is critically cleaned and optimized for maximum efficiency. Once you have gotten the hang of it, you can easily inspect the faults yourself and be able to do its maintenance a lot easier and faster.
Either natural gas or newer LP furnaces can be easily cleaned if you follow these simple instructions. Start by checking the igniter’s resistance using an ohmmeter. Carbide igniters should be at 50 to 100 ohms and silicon nitride ones should read at 11 to 17 ohms. If they are outside these parameters then the igniter should be replaced. Next is to check the flame sensor by hooking up the flame sensor and sensor wire to the multimeter in series and fire the furnace in a heat cycle. You should get a reading of 1.5 to 4 uA. Any lower than this then it might stop sensing completely.
Continue your furnace cleaning by pulling and cleaning the burners. They are usually contaminated and misaligned. There are slots or ‘wings’ that help align to the burner next to it. Clean them from debris that could block the flow of air and gas. Clean the heat exchangers from rusts, cracks or holes. You could inspect them manually, but this would require experienced eyes. You could inspect using inspection cameras for the metal flue and ensure that it is supported properly. The condensate lines are crucial to the performance of 90%+ furnaces. The P-trap and pressure tubes must be removed or blown out to clean them from debris.
The next step to your furnace cleaning is to check the system static pressure. Depending on your type of non-variable-speed motor or variable-speed motor, you should set the external static pressure. The former maxes out at .50-in wc while the latter is at .80-in wc. Make sure to refer to a fan chart in order to set the correct cfm of the furnace. Afterwards, perform a combustion analysis. The purpose is to gain the optimum CO levels. Measure the highest CO level during first 60 seconds of combustion. It is only safe if the CO levels drop to 100ppm within three minutes after activation.
Next is to check for gas leaks. For this you can either use soap bubbles or an electronic detector, though the latter may sometimes give false-positive on certain brands. Then make sure that the vent pipe is properly supported. Place pipe-support hangers every 3 ft. of the PVC. Finish your furnace cleaning by setting the heat-off delay. Setting it to 180 seconds will provide the best efficiency. Although all these steps are easily followed, make sure to read the furnace’s manuals so that you can alter the requirement needs of your furnaces accordingly.