Since about April, your furnace has done nothing but sit in a hall closet, attic or garage while the air conditioner carried the house through summer. A furnace inspection is the visit where someone opens that cabinet, runs the system under load and confirms it is still safe to burn gas in your home before you start relying on it every night.

That long rest is exactly why the visit earns its place in Las Vegas. Sitting idle doesn’t wear parts out the way running does, but it hides problems. Dust settles on the burners. A hairline crack that formed near the end of last winter stays invisible. An ignitor that was already weak goes into the season one year older. None of it announces itself until the system is asked to make heat, and by then you want heat, not a diagnosis.

October Beats the First Cold Snap

The U.S. Department of Energy's home heating and cooling guide recommends having furnaces checked in the fall and air conditioners in the spring. On the safety side, the CDC lists a yearly service visit for the heating system, the water heater and every other appliance that burns gas among its main ways to prevent carbon monoxide exposure.

In the Valley, fall usually means October or the first half of November, while daytime temperatures are still mild. Booking then has a practical upside too. If the technician finds a part that needs ordering, it can arrive while you still don't need the heat.

The Visit, Part by Part

A thorough furnace safety inspection follows the path that fuel, flame, exhaust and air take through the system. Here is what that looks like on a typical gas furnace.

The Call for Heat

The technician starts outside the cabinet. They set the thermostat to call for heat and watch the startup sequence from beginning to end, confirming that each stage happens in the right order and that the thermostat is reading the room accurately. A furnace that hesitates, starts twice or stalls partway through is already giving clues before any panel comes off.

Burners and Ignition

Inside the burner compartment, they look at the flame itself. Burners that have collected dust or debris over the summer can light unevenly or late, and late ignition is what produces the hard thump some furnaces make at startup. The ignitor gets checked for cracks and wear, since hot surface ignitors are fragile and tend to fail without warning. The flame sensor, the small rod that tells the control board a flame is present, is checked and cleaned if it has built up a coating.

The Heat Exchanger

This is the part most people mean when they talk about a furnace being safe. The heat exchanger is the metal chamber that keeps combustion gases on one side and the air you breathe on the other. The technician inspects it as far as the design allows, looking for cracks, rust, scorch marks and soot. Some areas can only be seen with a camera or by watching how the flame behaves when the blower kicks on, which is why this step can't be done properly from outside.

Flue and Venting

Exhaust has to leave the house completely. The technician follows the flue pipe from the furnace to where it exits, checking joints, slope, supports and the termination for blockages. High-efficiency furnaces vent through plastic pipe and also produce condensation, so their drain line and trap get checked here as well.

Gas Supply

Using a gauge, the technician measures gas pressure at the furnace and compares it with the manufacturer's specification. Pressure that is too high can overheat the heat exchanger. Pressure that is too low can cause poor combustion and soot. Connections and the gas valve are checked for leaks.

Safety Controls

Furnaces carry several switches whose only job is to shut everything down when something goes wrong: the high-limit switch for overheating, rollout switches for flame escaping the burner area, and a pressure switch that confirms the exhaust path is clear. Each one should be tested to confirm it would actually do its job, rather than assumed to work because the furnace runs.

Airflow, Filter and Temperature Rise

Last comes the air side. The technician checks the filter, the blower wheel and the motor, then measures the difference in temperature between the air going into the furnace and the air coming out. That number, called temperature rise, should fall within a range printed on the furnace label. A reading outside it usually points to an airflow problem or a combustion problem worth chasing down.

Carbon Monoxide Readings

A thorough inspection ends with combustion and carbon monoxide readings taken while the furnace is running at full heat. A visual check of the heat exchanger tells you what the metal looks like. Instrument readings tell you what the furnace is actually putting into the flue and the air around it.

What a Desert Summer Does to a Furnace

Las Vegas furnaces face a few conditions that furnaces in colder places mostly don't.

Dust with nowhere to go. Fine desert dust works its way into closets, garages and attics, and a furnace that isn't running has no airflow to move it along. It settles on burners, the blower wheel and the flame sensor all summer.

Attic heat. Many homes in the Valley have their furnace in the attic, where summer air gets far hotter than anywhere in the living space. Months of that can be hard on wiring, rubber parts and the furnace's own drain components.

One appliance doing two jobs. In most homes, the furnace blower also moves air for the AC, so it works hard all summer even while the burners sit cold. A blower that has been running hot since June may be the first thing to struggle once heating season begins.

If a burning-dust smell appears the first time the heat comes on, you can check it against the list in our post on a burning smell from your heater to see whether it is the harmless kind.

Electric Furnaces and Heat Pumps Get a Different Checklist

Without a flame, there is no heat exchanger, flue or gas pressure to check. An electric furnace inspection focuses on the heating elements, sequencers, wiring connections, limit controls and blower. A heat pump inspection adds the outdoor unit: the coil, refrigerant pressures, the defrost controls and the backup heat strips that help on the coldest nights. The safety stakes are lower without combustion, but electrical connections that have loosened over a hot summer are still worth catching.

Reading the Results

The useful part of any furnace inspection is the explanation at the end. Ask the technician to separate what they found into two groups: anything that affects safety, and anything that affects comfort or efficiency. A dirty flame sensor and a cracked heat exchanger are not the same kind of finding, and you should never be left guessing which group an item falls into.

If you are told the heat exchanger is cracked, ask to see the evidence. A photo, a camera view or a carbon monoxide reading should back the call up. This is the one finding that often leads to a conversation about replacing the furnace, so it deserves to be shown rather than simply stated. A technician who is confident in the diagnosis won't mind.

Most findings on a healthy furnace are small: a filter, a sensor cleaning, a loose wire tightened. Those are the problems an annual visit exists to catch while they are still small.

Making the Visit Go Smoothly

Clear a few feet of space around the furnace, including anything stored on top of it or against the cabinet. If it lives in the attic, make sure the access hatch isn't blocked. Then jot down anything you noticed last winter: rooms that never warmed up, odd sounds, a smell, a carbon monoxide alarm that chirped. Small details like these help the technician know where to look harder.

Booking a Furnace Inspection

If your furnace hasn't been looked at since last winter, now is the easy time to do it. You can book Dr. Cool's heating maintenance visit with upfront pricing, and if you would also like the air in the house tested, carbon monoxide detection is part of our indoor air quality service. Reserve a time online, or call (702) 873-1800 before the weather turns.