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Gas Furnace Maintenance Procedures | Tips for HVAC Contractors

Last updated: 03-03-2021

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Gas Furnace Maintenance Procedures | Tips for HVAC Contractors

Gas furnace inspections are an important part of your work as an HVAC contractor. Your clients rely on you toperform general inspections and tune-upsthat keep their heating systems running strong all winter long. A furnace inspection allows you to make your clients aware of potential issues or repairs that may need to be done on their gas furnace.

Any time you’re conducting maintenance on a gas furnace, thoroughness and attention to detail are key. When you first arrive at the client’s home, it’s a good idea to watch the furnace run for a few minutes to look for any signs of a problem. From there, you can shut it off to begin maintenance.

And remember: While we are providing some general guidelines for inspecting gas furnaces in this blog post, it is important that youalwaysdefer to manufacturer guidelines and instructions while working on anyheating equipment.

In general, you’ll want to begin a gas furnace inspection with some basic tune-up tasks. This includes checking the air filter and either cleaning it out or replacing it as needed. From there, you should also take a look at the blower wheel and motor assembly. If possible, lubricate the motor. If the furnace is a newer one, it will probably have sealed bearings, and this step will not be necessary.

Next, it’s time to check the inducer motor. Some older inducers actually had oil ports on them, but newer models will likely have sealed bearings that should not require your attention. Still, you’ll want to take the time to check on the condition of the ignitor.

Over time, the burners on a gas furnace can accumulate a lot of dirt and debris, so you should pull out each burner and clean it out as part of your furnace tune-up. Typically, the best way to do this is to carefully brush the debris off each burner and vacuum them individually.

While you’re at it, you can pull out the lower part of the heat exchanger and vacuum it out as well. This is especially worth your time for a furnace that runs on propane gas, as the burners on these furnaces tend to rust very easily due to impurities in the gas itself. By taking the time to clean these burners with each maintenance visit, you can prolong the life of these parts.

The condensate that drains out of gas furnaces is very acidic and can deteriorate hoses over time. This causes the hoses to swell and develop small tears, which can create major problems. For this reason, it’s important to check all drain hoses as part of your inspection.

Another thing to watch for is how the hose is lying on the bottom of the cabinet itself. Sometimes, the placement of a hose can trip the pressure switch. If this is a problem, you will want to recommend that these hoses be replaced completely. This is something you can likely handle same-day, assuming you have additional hosing supplies in your work truck.

In addition to checking the hoses, it’s also a good idea to inspect and clean all drain traps on a condensing furnace. This should include removing the trap, flushing it out and thoroughly cleaning it. Be sure to pour some clean water back into the collector box to fill the trap after you drain it out, as this is critical to the performance of the furnace itself.

Don’t forget to carefully check pressure switches as part of your inspection. This should include manually pulling the tubing off the switches to make sure they’re not cracked, dry rotted or otherwise damaged. Just be careful not to blow any air into the pressure switches themselves, as this can cause damage to the diaphragm. Sometimes, inexperienced HVAC technicians will accidentally blow air into pressure switches while they’re flushing out and cleaning drain hoses, so this is just something to be aware of and avoid.

Taking the time to check and tighten electrical connections is vital, even on a gas furnace. Specifically, you’ll need to make sure every connection is properly grounded. This is especially important because, in a gas furnace, flame rectification is necessary for flame proving. The furnace needs proper grounding through a circuit that runs through the flame.

Checking and adjusting manifold pressure should also be a key part of your inspection and tune-up on a gas furnace. You should always follow your manufacturer’s instructions and guidelines here. On multi-stack and variable-capacity modulating furnaces, you’ll want to also check the gas meter during your maintenance visit. This is a good way to actually show the BTU operation to the client.

Keep in mind that when you clock a meter, you should shut off all gas appliances (and their pilot lights) for an accurate reading. Many HVAC professionals find that it’s useful to print out a copy of a meter-clocking chart to laminate and keep in their work trucks. This can serve as a useful reference and save you from having to Google normal readings with each of your scheduled maintenance visits.

One of the more complicated procedures you’ll need to carry out during a gas furnace inspection is analyzing the equipment’s combustion and temperature rise. There are plenty of great tools out there that can make this task easier, such as a combustion analyzer.

Specific readings will depend on many different factors, including the age of the furnace itself and whether it is a stack model or an older, non-induced draft model. Check the manufacturer’s instructions and guidelines to know what readings are normal versus abnormal.

Temperature riseis another metric that you’ll want to check as part of your tune-up and inspection. Ideally, the temperature rise on the furnace should be somewhere in the middle of the “normal” range. For example, if the rise on the furnace is listed as 30 to 70 degrees, your reading should be somewhere in the middle, around 50 degrees. If your reading is at the high or low end of the range, then this may require some further investigation on your part.

Before you complete your inspection, there are a few odds and ends you’ll want to tackle. This should include checking for signs of gas leaks and bringing any issues to the client’s attention.

This is also a good time to check and see if the home has carbon monoxide detectors. Ideally, theseshould be placed on each floorof the home where gas appliances are present. If there is not a carbon monoxide detector in sight, this is worth bringing up to the homeowner. Even if carbon monoxide detectors are present, you may want to remind your clients to test these devices at least a few times a year to ensure they are working properly. After all, most carbon monoxide detectors have lifespans ofabout 5-7 yearsbefore they need to be replaced or upgraded. This is something a lot of homeowners don’t realize.

Before you leave, you should also take the time to check the furnace flues and clean out any leaves or other debris accumulated inside the flues themselves. Debris inside these flues can cause blockages that will affect the pressure switch’s operation down the road, so this is not a step you’ll want to skip.

You may also want to check for any visible sags in the furnace piping. A sag could cause water to be retained along the piping, which could eventually cause the pressure switch to trip.

There are many steps that an HVAC professional needs to remember to follow during a routine inspection and tune-up. And while this is not meant to be a comprehensive list of everything you’ll do during a residential inspection, it does include a handful of the most important items that should be on your list.

By performing the most thorough inspection and tune-up possible, you can help your client prolong the life of their gas furnace. At the same time, you can mention items to the client that may require attention either in the short- or long-term, such as a clogged drain line or a blower motor that is showing signs of wear and tear.

By reminding homeowners to install and test carbon monoxide detectors around areas of the home that utilize gas appliances (including furnaces), you can do your part to keep your clients and their loved ones safe!


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