How often does a furnace really need servicing?

Once a year. That is the interval every furnace maker prints in the manual, the one most parts warranties hinge on, and the one that fits the Ottawa heating season, which runs from the first frost in October to the last cold snap in April. Over those seven months a gas furnace in an Ottawa house logs more burner hours than one in Toronto or Hamilton, so a yearly service here is not a nice-to-have. It is the minimum.

When in the year to book it

Late September or the first half of October. The furnace has sat idle since April, the dust that settled on the burners over the summer is about to be cooked, and any part that has quietly failed will show itself on the first cold morning. Finding that in October means the part is ordered and fitted on a mild afternoon. Finding it in the third week of January, when every heating company between Kanata and Orléans is running a waiting list, means a cold house and a premium price. If you have missed the fall window, book anyway; the furnace still has four months of hard running ahead of it.

What seven months of running does to a furnace

An Ottawa furnace fires for somewhere between 1,800 and 2,400 hours a season, depending on the house and the winter. Over that time:

• The flame sensor, a thin metal rod in the burner flame, collects a film of oxidation and silica that stops it reading the flame. The control board then shuts the gas off a few seconds after ignition. This is the single most common fault we see on service calls, and cleaning the rod takes ten minutes.
• The condensate trap on a high-efficiency furnace fills with sludge. A blocked trap backs water into the pressure switch tubing and the furnace refuses to light.
• The hot-surface igniter, a brittle ceramic element, ages with every start. A furnace that short-cycles ages it faster.
• The blower wheel collects whatever the filter let through, which is a lot in a house with pets or with a one-inch filter left in for a season.
• Gas pressure at the manifold drifts, and the burner flame drifts with it, toward a yellow, sooting burn that wastes gas and loads the heat exchanger.

None of these stops the furnace on its own. Two or three of them together are why a furnace that ran fine in March will not light in November.

What a real service includes

A furnace service and a furnace glance are different things. A technician who changes the filter, looks at the flame and leaves has not serviced the furnace. The job, done properly, takes about an hour and covers the following. Ask which of them were done.

• Burners pulled or brushed, flame checked for a steady blue burn.
• Flame sensor cleaned and its microamp signal measured, not just wiped.
• Igniter inspected for cracks and its resistance checked.
• Heat exchanger inspected for cracks and corrosion, and carbon monoxide measured in the supply air. A cracked exchanger can push combustion gases, including carbon monoxide, into the air the blower sends through the house, and it is the one fault that retires a furnace on the spot.
• Combustion analysis on the flue gas: oxygen, carbon monoxide and flue temperature. This is the test that proves the furnace is burning cleanly and at its rated efficiency.
• Gas pressure set to the rating plate.
• Every safety control exercised: high-limit switch, rollout switches, pressure switch, door switch.
• Venting checked end to end. A high-efficiency furnace vents in plastic pipe through the wall, and the terminations outside need to be clear, sloped correctly and above the snow line.
• Condensate trap flushed, drain line cleared, neutralizer checked.
• Blower wheel inspected, motor amperage measured, capacitor tested.
• Filter replaced and the filter cabinet checked for bypass.
• Thermostat checked, including the changeover settings on a hybrid heat pump system.
• A written report with the readings.

Any work on the gas side of a furnace in Ontario has to be done by a TSSA-certified gas technician. That is the legal floor, not a selling point, and you are entitled to see the certificate.

Does a furnace under five years old need it?

Yes, and for a reason that costs money if you ignore it. Most manufacturer parts warranties, including the ten-year heat exchanger warranty on the builder-grade furnaces fitted across Kanata, Barrhaven and Stittsville in the 2010s, require proof of annual professional maintenance. Skip three years and a warranty claim on a control board or an exchanger can be refused.

The jobs that stay with you

Between visits, a few minutes a month keeps the furnace in the shape the service left it in.

• Check the filter every month from October to April. A one-inch filter in an Ottawa winter rarely lasts past two months; a four-inch media filter usually makes a season. A loaded filter is the most common reason a furnace trips its limit switch.
• After every heavy snowfall and after a wind storm, look at the two plastic pipes on the outside wall. A drift over the intake or an ice cap on the exhaust shuts a high-efficiency furnace down, and it happens in Ottawa every winter, usually on the sheltered side of the house where the snow piles.
• Put fresh batteries in the thermostat each fall if it takes them. A thermostat with a dead battery looks exactly like a dead furnace.
• Keep a metre of clear floor around the furnace and nothing leaning on the vent pipes.
• Pay attention to new sounds. A bang on light-off, a new rattle from the blower, or a burning-dust smell that is still there on day three of the season are reasons to call before the scheduled visit.

What it costs and how to book

A full tune-up in the Ottawa area is typically $139 to $219; the written price is the one that counts. Book a furnace tune-up for September or October, keep the report with your warranty paperwork, and if something is found, ask for the repair price in writing before anyone starts. If the furnace is already misbehaving, start with a repair visit instead, and the service can be folded into it. How long a well-kept furnace should last, and what cuts that short, is in how many winters does a furnace have in it?. The phone is answered every day of the year.