Winter furnace maintenance for Phoenix homes

Phoenix winter is short. It is also the furnace's whole career.

Sky Harbor's normal December low is 45.3 degrees; January's is 46.0, according to the National Weather Service. Those numbers do not impress anyone from Minneapolis, and they are not trying to. They describe the few weeks a year when a Phoenix furnace does nearly all of its work, packed into cold mornings and colder evenings.

Concentrated use means concentrated wear. The filter loads faster. The ignitor starts more often in a week than it did all summer. And because the season is short, a breakdown never seems worth worrying about, right up to the night it happens.

Signs your furnace needs attention now

• It starts, stops and tries again. Short cycling often points to a dirty flame sensor or a furnace overheating behind a clogged filter.
• It blows cool air. On a gas furnace that can mean the burners are not lighting. On a heat pump it may simply be a defrost cycle.
• It makes new noises. A boom when the burners light, a squeal from the blower, a rattle that was not there last year. A boom at ignition, in particular, deserves a prompt call.
• The flame looks wrong. Burners should burn steady and blue. Yellow, lazy or wandering flames suggest a combustion problem.
• The carbon monoxide alarm sounds. Follow the CPSC's advice: get outside to fresh air immediately, then call 911.

And a word on the reset habit. Turning the thermostat off and back on once is reasonable. Resetting a furnace that keeps locking itself out is like pressing snooze on a smoke alarm. It locked out for a reason. Call.

What a winter maintenance visit covers

If your furnace had a fall tune-up and is behaving, you likely do not need another visit this season. A winter visit makes sense when the fall one was skipped, when a furnace is older or works unusually hard, or when something has started to seem off. The technician checks combustion and the flame sensor, the ignitor and safety switches, the heat exchanger, the flue and vent, the blower and the filter, and tests for carbon monoxide. On heat pumps, the defrost cycle and the backup heat get the same scrutiny.

Our heating and furnace repair page covers what happens when the diagnosis turns into a fix. Every repair is quoted flat-rate before any work begins.

Thermostat habits that help

Setting the thermostat to 85 does not make a furnace hurry. It only makes it overshoot, and then you open a window. Pick a comfortable setting and leave it, or let a smart thermostat handle the schedule. Our notes on thermostat settings for the desert cover both seasons, and keep the vents open: closing vents does not save money.

When a cold night is more than an inconvenience

If someone in the house feels the cold more than most, or the home is a rental you are responsible for, a furnace failure on a 40-degree night is not a story for later. Get the check done before the coldest stretch, keep the carbon monoxide alarms tested, and keep our number handy for emergency heating repair.