Furnace maintenance: what to know

What the job involves, what changes the price, and what to ask a pro.

What furnace maintenance is

Furnace maintenance is an annual tune-up of a gas, oil or electric furnace. The technician cleans the parts that foul, checks the safety controls and the heat exchanger, and tests the system before cold weather arrives.

Signs you need it

  • It has been about a year since the last tune-up, or the furnace has never been serviced since it was installed.
  • The gas burner flame is yellow or flickers instead of burning steady blue.
  • The furnace runs longer than it used to in order to reach the same temperature.
  • The filter is coated with dust within a few weeks of changing it.
  • You hear new squeals, rattles or bangs when the blower or burners start.
  • A rotten-egg smell or a carbon monoxide alarm means you should leave the house and call for help before anything else.

What the pro does

  • Shut off power and clean the burners, the flame sensor and the igniter, then check the flame pattern on a gas unit.
  • Inspect the heat exchanger for cracks, rust or soot, and run a combustion test to measure carbon monoxide in the flue gas.
  • Check the blower motor, belt or capacitor, lubricate motors that need it, and measure airflow across the filter and blower.
  • Test the safety controls, including the limit switch, the pressure switch, the flame rollout switch and the gas valve operation.
  • Clear the condensate drain and trap on a high-efficiency furnace, and check the vent pipe for blockage.
  • Confirm the thermostat calls for heat, the furnace cycles correctly and the temperature rise falls within the manufacturer's range.

What changes the price

Every job is different, so we do not publish prices. These are the things that move the quote up or down.

  • Fuel type and design. Gas, oil and electric furnaces need different checks.
  • Number of burners, and whether the blower is single-speed, multi-speed or variable-speed.
  • Whether the furnace is high efficiency, with a condensate drain and plastic vent pipe that need service.
  • Access to the furnace, such as a tight closet, an attic unit or a crawl space, which adds time.
  • Extra work found during the tune-up, such as a worn belt, a failing capacitor or a clogged drain.
  • Whether the visit includes a full combustion analysis and written report, or only a basic check.
  • Whether the home has a second system, such as a separate air conditioner on the same ductwork, that also needs checking.

What a written quote should spell out

  • Each tune-up task listed, with the burner cleaning, combustion test and safety control checks named.
  • The combustion and carbon monoxide readings recorded and shared with you.
  • Recommended parts, such as a belt, igniter or filter, listed separately from the tune-up.
  • Repairs found during the visit, listed as separate items that are not started without your approval.
  • The filter size and the recommended change interval for the unit.

Questions to ask before you hire

  • Will you run a combustion test and check the heat exchanger for cracks, and will you show me the readings?
  • Do you clean the burners and the flame sensor, or only check them?
  • Which safety controls do you test during the tune-up?
  • If you find a problem, will you call me before doing any work beyond the tune-up?
  • Do you service my brand and fuel type, and do you carry the parts on the truck?
  • Will you give me a written report I can keep with my home records?

Red flags

  • The pro recommends a full replacement at the start of a basic tune-up without showing measurements.
  • The tune-up on a gas furnace skips the combustion test or the heat exchanger check.
  • The pro will not show the readings or the failed part.
  • The visit takes a few minutes with no cleaning, no control testing and no written report.

What you can do yourself

Replace the filter on the schedule your furnace needs, and keep the area around the furnace clear. Confirm the thermostat works and that the supply registers and returns are open. Leave burner cleaning, combustion testing, heat exchanger checks and all gas or oil work to a licensed technician.

Licenses and permits

Furnace maintenance is commonly done by licensed HVAC technicians, and gas and oil work may fall under additional trade rules. Check with your state or local licensing agency for the requirements that apply to this service.

Furnace maintenance questions

How often should a furnace get a tune-up?

Once a year, before the heating season, is the usual schedule. Booking before the first long cold spell lets any fault show up while a repair is still easy to schedule.

Does a tune-up prevent a furnace from failing?

It catches many faults early, such as a cracked igniter, a weak capacitor or a clogged drain. It cannot prevent every failure, but the written report shows what is wearing and how fast.

Why does my furnace smell dusty when it first starts up?

Dust that settles in the ducts and on the heat exchanger often burns off at the start of the season. A smell that lasts, or smells like something burning, should be checked. A rotten-egg smell or a carbon monoxide alarm means you should leave the house and call for help.

About this guide

This national guide is written and checked by infinibell. Rules and conditions differ by place, so local pros are credited on guides for the cities they serve, not on national ones.

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