Your Complete Gas Furnace Inspection Checklist

Don't wait for outside temperatures to take a dip to check in on your furnace and ensure that everything's working properly. Regular furnace maintenance, along with an annual inspection from a qualified furnace pro, will help you avoid breakdowns that can leave you chilly on a frigid day. Here’s a complete gas furnace maintenance checklist to follow to keep your furnace burning and your feet toasty. 

Follow This DIY Furnace Maintenance Checklist

First, let’s cover some basic gas furnace maintenance tasks you can do to keep it running in top shape. 

1. Change the Filters

You should change furnace filters on this schedule:

• No pets: every 90 days

• With pets: every 60 days

• If someone in your home has allergies: every 30–45 days

If you don’t change your filters regularly, dirt, debris, and particles can build up and slow airflow—which means less efficiency.

2. Clean the Burners

Your burners should be removed and cleaned every so often. Burners are susceptible to soot and condensation that can prematurely age your furnace. While a pro will do this as part of an annual check-up, you can and should check them yourself as often as you change the filters.  

After turning off the furnace and shutting off the gas valve, remove the burners and vacuum or wipe them down with a cloth. The flame sensor, which detects whether the pilot light is on, should also be cleaned at the same time. Take it out and remove any dirt with a cloth. 

3. Check the Gas Line

Check for signs of leaking—like a hissing sound or a tell-tale smell of propane—starting from the shut-off valve. If you hear a hiss or smell propane, shut off your main valve and call a pro right away.

4. Test the Smoke Detector and Carbon Monoxide Detector

While your home's smoke detector and carbon monoxide detector aren't part of your gas furnace, your furnace inspection is a great time to remember to test and replace the batteries in them. 

You should also test your carbon monoxide detector. Make sure your detectors are at least 15 feet away from your furnace to avoid false alarms from the small amount of carbon monoxide (CO) given off when your furnace is starting up.

What to Expect During an Annual Furnace Inspection

An annual furnace inspection check-up will cover all of the easy DIY tasks above, as well as some more complicated steps best left to a furnace technician. Here’s what to expect during your annual inspection: 

1. Clean and Oil the Motors and Bearings

A furnace pro will clean and lubricate internal furnace components to extend their life and prevent failure. Many furnaces have four bearings, two motors, and two blower shafts. They both need to be oiled at least once a year to keep them running smoothly.

2. Check Thermostat

The thermostat should be checked for functionality and accuracy. Common signs that your thermostat is not working properly include your furnace not producing heat, vast temperature swings, or the furnace cycling on and off frequently. 

The furnace pro will check that there is no dust or debris on the thermostat and that it’s still working properly. You can also ask them to recalibrate your thermometer to help reduce energy costs.

3. Inspect Ignition and Flame

Your HVAC pro will cycle the furnace on and off to check ignition and flame performance. The ignition is a vital part of the furnace as it creates the spark needed to heat the air. 

Once they check the ignition, they will assess the color of the sparked flame to determine how much oxygen the furnace is receiving. They may replace your ignitor or adjust the pilot valve if necessary. 

4. Flush Drains and Traps

The HVAC specialist will also flush the furnace’s drains and traps and check for leaking water during the inspection. Water leaks are signs of issues like: 

• Loose connections

• Cracks

• Holes within the condensate drain line

Most furnaces have at least two internal drains that connect to the unit's trap. These drains help to clear the heat exchanger and vent.

It's essential to drain condensation to prevent accumulation that could stop the combustion. Flushing the drain and traps can also identify if there is a drain line clog.

5. Check Venting

Confirming that vents are clear is important because the furnace vents direct gas away from your home through the flue pipe. The furnace inspector will verify that there is proper, unobstructed ventilation by looking for debris, leaks, and sloping. 

Common signs of clogged venting can include rust and water streaks on your furnace's vent or flue.

6. Inspect and Clean Blower

The furnace pro will next remove and clean the blower motor, which is responsible for controlling the airflow of the heating and cooling system. The blower powers the fan of the furnace, which helps circulate air out of the system. 

The performance of the blower's run capacitor, which acts like a battery for the blower, should also be checked.

7. Adjust and Tighten Panels

Your furnace pro will ensure that all unit panels are tightly in place because jostled panels can reduce efficiency, make rattling noises when running, and potentially cause a system shutdown. A front panel that doesn't close properly could also put your home at risk for unhealthy carbon monoxide (CO) exposure.

8. Check Controls and Safeties

Controls and safeties should be tested to verify that they won't interfere with the performance of other components. Controls and safeties have built-in triggers that preempt dangerous malfunctions and overloads. 

Your furnace's main safety feature is the limit switch that shuts off the gas supply if heat or flames are detected beyond the unit's burner chamber. Your furnace may also feature controls that display error messages. Furnaces typically will not restart once a control or safety is triggered and must be manually reset.

9. Check Flue Pipe

The flue pipe is responsible for removing fuel by-products from your home. A pro will check your flue pipe for the right fit and flow. They will also check for any corrosion, loose joints, water stains, or soot deposits on the pipe. 

If the flue pipe is not functioning properly, exhaust gasses may build up in your home, which can cause very dangerous exposure to carbon monoxide. 

10. Check Heat Exchanger

The next step in your furnace inspection is to check the heat exchanger. Heat exchangers are responsible for mixing cold and hot air. This activates the heat transfer of the furnace to make sure the temperature reaches equilibrium. 

Heat exchangers only require visual inspections. Some tell-tale signs that an exchanger is having an issue include a formaldehyde-like smell, soot, cracks, and noises.

11. Check Manifold Pressure

Your pro will check and adjust the manifold pressure. The manifold pressure is the gas pressure delivered from the gas valve to the burners, which supplies the heat energy. 

The pressure should be set between 3.2 WC and 3.7 WC. If the pressure is too low, it can cause incomplete combustion. If it’s too high, it can put too much strain on your furnace, which can lead to a shorter lifespan. 

12. Inspect Air Openings

You'll find your furnace's air intake vent located on the side of your house, and its return ducts are typically placed in rooms, hallways, and stairwells. Vent blocks can cause anything from carbon monoxide buildup to pressure imbalances that make your unit inefficient. 

As part of the maintenance appointment, the pro will inspect all openings for blockages or restrictions. Dust, mold, pollen, pet dander, leaves, hair, soil, and critters can all get into your air openings to create blockages.

13. Perform Extra Services

Most furnace inspections rely on visual and performance-based inspections of key components. You can often upgrade your inspection to include:

• Static air pressure test

• Temperature-rise assessment

• Gas-pressure testing

• Combustion-gas analysis

These test points can serve as important performance measures if you have an older unit.

Bonus Step: A General Cleaning

Dust is common on furnaces because they’re usually found in basements and utility closets, so you can also routinely wipe down the furnace’s surface and vacuum around it to keep the area clean. If you hire a professional tech to service your furnace, they will clean it for you and leave your furnace area in pristine condition following an inspection.

How Much Does a Furnace Inspection Cost?

The average cost of an HVAC inspection ranges from $60 to $85, which is a worthwhile price for the long-term benefits. Regular maintenance also ensures that your system lasts longer, prevents major breakdowns, and avoids energy bill jumps. 

If the technician discovers something wrong with your furnace, you can ask for the inspection cost to be removed from your final repair bill. 

Make a Plan to Get Your Furnace Checked

If you're just learning that gas furnaces need to be inspected every year, get in contact with a local HVAC contractor today to book an appointment. Most pros will put you on a service plan that includes your annual inspection with some free service calls thrown in the mix.

If you suspect that your furnace is damaged or needs repairs, you can call your HVAC technician before their yearly visit to assess your furnace. Depending on the damage, the cost of a furnace repair ranges from $130 to $500. If there is significant damage to your furnace, or it is over 20 years old, it might be time for a replacement. The average cost for a furnace replacement can range from $2,800 to $6,800.

While a furnace pro is important for your annual inspection, you shouldn't stay away from your furnace the rest of the year. Regular furnace check-ups protect your furnace warranty; some warranties become void if you don't properly maintain your unit.

Regular furnace check-ups also save you money by boosting your system's energy efficiency—which means no surprise heating costs flying at you. You can even catch a pricey problem before it happens.

Spend the time to:

• Pop into the furnace room regularly to look for signs of leaks, corrosion, or strange odors. 

• Put filter changes on your calendar every 30 to 90 days.

• Schedule a furnace check-up once a year.

Taking care to keep the furnace area clean and properly ventilated will boost its efficiency and dependability through many more cold months.