How often should you service your furnace?

Why bother

A tune-up catches a cracked heat exchanger. This is an essentials-tier job. Skip it and you're inviting the expensive kind of problem, or the dangerous kind.

Why it's a range

Once a year before the cold is the standard, worth it for the cracked-heat-exchanger check alone. An old furnace working hard wants the look more than a near-new one. Annual is also the figure most warranties quietly require.

What the job involves

1. Book the pro for late summer or early fall, before the heating season starts and before every other house on the street has the same idea. The technician cleans the burners, blower and the heat exchanger (the metal wall that keeps combustion gases out of the air you breathe) and checks it for cracks.
2. Let them run the combustion and gas-pressure tests, check the flue for leaks, and confirm the furnace isn't producing carbon monoxide. This is the part that needs tools and training, so it's the part you watch, not do.
3. They'll replace or clean the air filter, oil the moving parts, check the thermostat and tighten the electrical connections while they're in there.
4. Between yearly visits, swap the furnace filter every one to three months yourself. A few dollars, two minutes, and the system isn't left choking on its own dust all winter.

Do it yourself, or pay someone?

Hire a pro for the service itself. A yearly tune-up runs about $150 to $200, and combustion testing plus a heat-exchanger inspection need tools and training a homeowner hasn't got, with carbon monoxide on the line if it's missed. The one DIY part is the filter: keep it changed every one to three months.

What skipping it costs

$1,250 to $10,000, and that's only the money. The cheap end is replacing the cracked heat exchanger a service would have caught, around $1,250 to $3,000. The dear end is what a missed crack or a long-neglected unit forces: a whole new furnace, $4,200 to $7,175. Sitting underneath the figures is the part that doesn't price up neatly, a cracked heat exchanger or a faulty burner can leak carbon monoxide into the house. A yearly visit and a working CO detector is the defense. The visit is $150 to $200.

Signs it's overdue

• A yellow or orange burner flame instead of a crisp blue one, or the carbon monoxide detector going off. That can mean incomplete combustion or a cracked heat exchanger. Leave the house and call for service straight away, this one isn't a wait-and-see.
• Banging, rattling or screeching, or the furnace short-cycling, kicking on and off many times an hour. That's worn or strained parts asking for attention before they pack in entirely.
• Heating bills jumping with no change in the weather. A dirty unit runs harder to do the same job, so the cost shows up on the bill before it shows up anywhere else.

When to start thinking about it

This usually means booking someone, so the grumbling starts 28 days ahead to leave time to line it up. Mark it done and Grumpty sets the next one, every 12 months, so you can go back to forgetting it exists.

Questions people ask