Fall Furnace Tune-Up: What We Check Before Michigan Winter

It's August. Your air conditioning is running, the lake is warm, and nobody wants to hear a furnace guy talk about heating season.

Book it now anyway.

Not because the furnace cares what the calendar says. Because of what happens on the first genuinely cold night in West Michigan — that week in October or early November when the temperature drops twenty-five degrees overnight and half of Ottawa and Kent County turns the heat on for the first time in six months. Every marginal furnace in the area picks that same night to fail. Our phones light up, every other heating company's phones light up, and a repair that would have taken one comfortable afternoon in September becomes a scramble.

A tune-up in August or September finds those problems on a week when nobody is cold, when parts are on the shelf, and when you have room to think about a repair-or-replace decision instead of making it at 11 p.m. in a house that's dropping a degree an hour.

So here's what actually happens when we come out, item by item. Not the glossy version — the real list, and why each piece is on it.

The Part That Matters Most: The Heat Exchanger

If a tune-up did nothing else, this would justify it.

The heat exchanger is the metal chamber that separates the flame and its exhaust gases from the air blowing through your house. It expands and contracts every single cycle, thousands of times a winter, for the life of the furnace. Eventually that metal fatigues, and on an aging furnace it can crack.

A cracked heat exchanger means combustion byproducts, including carbon monoxide, can mix into the air moving through your ductwork. You cannot see it, you cannot smell it, and the furnace will keep right on producing heat while it happens. That's what makes it different from every other failure in this trade. A bad blower motor announces itself. A cracked exchanger doesn't.

We inspect it visually with a light and a camera where the design allows, look for scorching or soot patterns that suggest a problem, and check the flame behavior when the blower kicks on — a flame that rolls or shifts when the fan starts is a classic tell. If we find a crack, the furnace gets shut down and red-tagged. That's not a sales tactic, it's the only responsible call, and I'll walk you through exactly what I saw.

Combustion and Ignition

This is where the no-heat calls come from, and most of it is cleaning.

The flame sensor. A thin metal rod that sits in the flame and confirms to the control board that the burners actually lit. It builds up an invisible film of oxide over a season, the board stops seeing a flame, and the furnace lights, runs a few seconds, and shuts down. Then it tries again. Then it locks out. That's the single most common no-heat call we run all winter, and it's a two-minute cleaning during a tune-up.

The burners. We pull and clean them, and we watch the flame pattern once they're back in. Burner flames should be steady, blue, and even across all of them. Lazy yellow flames, or one burner that looks different from its neighbors, means something is wrong with the gas-to-air mixture, and that's worth chasing down before winter.

The igniter. Hot surface igniters are a wear part, a filament that glows orange to light the burners and eventually burns out, usually with no warning. We check its resistance and look for cracking or thinning. Replacing one that's clearly on its way out during a scheduled visit is a lot cheaper than the same part at midnight in January.

Gas pressure. We verify the manifold pressure against what the data plate calls for. Overfiring stresses the heat exchanger and shortens its life. Underfiring means you're paying for heat you aren't getting.

Airflow and the Blower

Half of what people think is a heating problem is really an airflow problem.

The filter. We check it, and if it's due we change it. But this is the one piece of maintenance you should own between visits, and I've written a whole piece on how often to actually change it. A clogged filter starves the furnace, which overheats the exchanger and trips the limit switch, which is a manufactured problem you paid to create.

The blower wheel and motor. Dust builds up on the fins of the blower wheel and quietly kills airflow — a heavily loaded wheel can lose a big chunk of its capacity while looking basically fine. We check it, and we measure the motor's amp draw against its rating. A motor pulling high amps is a motor with a bearing going bad, and that's a repair I'd rather schedule than react to.

Duct and register basics. We'll flag obvious problems: crushed flex duct, disconnected sections in the crawl, supply registers that somebody closed off two winters ago and forgot about. If certain rooms never get warm, that's usually a distribution issue and there's more to that story than the furnace.

Venting, Drainage, and the Winter-Specific Stuff

Here's where West Michigan differs from the generic checklist you'd find anywhere.

Sidewall vent terminations. High-efficiency furnaces vent through PVC pipes out the side of the house, usually a couple of feet off the ground. That's fine in September. It's a real problem in February when we've had a stretch of lake-effect snow, drifts pile against the foundation, and those two pipes disappear. A blocked intake or exhaust shuts the furnace down on a pressure switch, which is the safe outcome — but it's a cold house. We check that the terminations are clear, properly spaced, and high enough to survive a real winter, and we'll tell you if yours are set too low for the drift line on your side of the house.

The condensate drain and trap. A high-efficiency furnace makes water. That's a byproduct of pulling the last usable heat out of the exhaust before it goes up the pipe. The condensate runs through a trap and drain line to a floor drain or pump. The line clogs with the same gunk that clogs an AC drain, and if any part of it runs through an unheated space, it can freeze. Either one shuts the furnace down. We flush the trap and line as standard.

The inducer motor. The small fan that pulls exhaust out through the vent. We listen to it and check its draw. Inducers usually get loud before they quit, so a bearing whine in September is a useful warning.

Safety Controls and Electrical

Limit and pressure switches. These are the devices that shut the furnace down if it overheats or if the venting isn't drawing correctly. We test them rather than assume. A safety switch that's failed closed is worse than useless, because it looks like everything is fine.

Electrical connections. We tighten what's loose and look for scorching at terminals. A loose connection arcs and generates heat right where you'd least want it, and the burnt terminal we find in September is usually the failed control board somebody else finds in January.

Thermostat. We confirm it's calling correctly, check the batteries if it takes them, and verify the cycle rate and staging are set sensibly for the equipment. A surprising number of comfort complaints are just a thermostat configured wrong at installation.

What a Tune-Up Won't Do

I'd rather set expectations than have you feel oversold in November.

A tune-up will not make a twenty-year-old furnace into a new one. It won't cut your gas bill dramatically — anyone promising that is selling, not servicing. And it won't guarantee you never have a failure, because parts fail without warning sometimes and I'm not going to pretend otherwise.

What it does do is find the safety problems you can't see, clear the failures that are already brewing, and give you an honest read on where your equipment stands. Sometimes that read is uncomfortable. I was in a basement in Wyoming last fall with a furnace pushing twenty-two years, still heating, but with a heat exchanger showing exactly the kind of stress pattern I don't like. The homeowner's first question was whether I was just trying to sell him a furnace. Reasonable question. So I showed him the camera footage, told him what I'd do in his position, and told him it was his call. He got two other opinions before he replaced it, and he should have. That's how this ought to work.

If a tune-up does turn up something significant, the repair-or-replace math is worth sitting with while the weather's still mild. That's the entire argument for booking in August.

Cost, and What to Do Between Visits

Most single-system tune-ups in this market run roughly $100 to $200. Companies advertising well below that are usually treating the visit as a sales opportunity, and you can generally tell by how quickly the conversation turns to a new system. Our furnace maintenance visit is a straightforward flat price, and Comfort Plan members have it included along with priority scheduling, 15% off repairs, and no overtime charges.

Between visits, your job is short: change the filter on schedule, keep the area around the furnace clear of storage, keep supply and return registers unblocked, test your CO detectors, and after a heavy snow, walk around and make sure those sidewall vents are clear. That last one takes thirty seconds and has saved more than one homeowner a service call. If something does go wrong mid-season, furnace repair is what we do, and you can book a visit online any time.