Fall furnace tune-up for Phoenix homes

The furnace has been asleep since spring. Wake it gently.

A Phoenix furnace lives a strange life. It sits in a garage, a hall closet or an attic that bakes all summer, and for months it does nothing but gather dust. Then one night the thermostat calls for heat, and a machine that has not fired since spring is asked to light a gas flame inside your home.

The calendar tells you when that night is coming. According to the National Weather Service, Sky Harbor's normal low falls from 65.6 degrees in October to 53.7 in November and 45.3 in December. Somewhere in that slide, every furnace in the Valley gets the same request on the same evening.

Why the fall, every year

ENERGY STAR recommends a heating check-up every fall. The Consumer Product Safety Commission and the CDC have long urged an annual professional inspection of fuel-burning heating systems, furnaces included, along with the flues and vents that carry exhaust out of the house. The reason is carbon monoxide, which the CPSC describes as colorless, odorless and toxic. You cannot smell a problem with a heat exchanger. You can only find it by looking.

The first heat of the season often brings a burning-dust smell. That is usually dust burning off inside the furnace, and it should fade quickly. A smell that lingers, a smell of gas, or a carbon monoxide alarm is a different matter entirely, and the answer is to stop and call.

What fails after a long idle summer

• Flame sensors. A thin metal rod that proves the burner actually lit. A light film of grime makes it doubt itself, and the furnace shuts the gas off seconds after lighting. It is one of the most common reasons a furnace starts, then quits.
• Ignitors. Hot surface ignitors are fragile and wear with every start. One near the end of its life likes to fail on the first cold night.
• Dust. Garage and attic furnaces collect it all summer. It coats burners, loads the blower and clogs the filter.
• Vents and flues. The CPSC recommends checking them for blockage, leaks and loose or disconnected sections. Birds and rodents have opinions about vent openings.
• Drains on high-efficiency furnaces. Condensing furnaces make water and need a clear drain to keep running.

What the tune-up actually covers

ENERGY STAR's heating checklist names the essentials: gas connections, gas pressure, burner combustion and the heat exchanger, plus electrical connections, controls and the thermostat. A proper tune-up covers all of them, cleans the flame sensor and burners, checks the ignitor and the safety switches, tests for carbon monoxide, and leaves you with a clean filter. You see what the technician sees. If a part is failing, you get a flat-rate price before any work begins.

Our heating maintenance page describes the service year-round; this page is about timing it to the Phoenix fall. For the full reasoning on when to book, read when to tune up your furnace in Phoenix, and for how these machines work, see the gas furnace guide.

If the tune-up finds something

Most findings are small: a sensor to clean, an ignitor to replace, a filter that should have been changed in July. If you want to know what repairs typically run before anyone opens the cabinet, we have written up what it costs to fix a furnace, the most common furnace repairs and the most expensive one, with published national figures. If your furnace stops working entirely, call for emergency heating repair.

Pair this visit with a fall AC check, and ask about our maintenance membership, which turns both into appointments you never have to remember.