Furnace Safety Before Heating Season: Cracked Heat Exchangers, Carbon Monoxide, and What a Home Inspector Actually Checks

A home inspector's furnace check is visual and functional.

We operate the system through a heating cycle, observe the burners and the flame pattern, look at the venting from the furnace to the exterior, check the accessible gas connections, and note the age and condition of the equipment. What we do not do is dismantle the unit or certify that the heat exchanger is free of cracks. Under the InterNACHI Standards of Practice, inspecting the interior of flues, chimneys, and heat exchangers is outside the scope of a home inspection. That work takes a combustion analyzer and a camera scope, and it belongs to a licensed HVAC technician.

That distinction matters more in October than in any other month. Once the furnace starts running daily in Northeast Indiana and the house stays closed until April, a venting problem that was harmless all summer becomes a carbon monoxide problem. This post covers what Indiana Inspections looks for, what no inspector can see, and what should send you to a technician before the first sustained cold week.

Why does carbon monoxide risk go up in Indiana homes in winter?

Three things arrive at once. The furnace starts producing combustion gases daily. The house is sealed against the cold, so anything that leaks indoors stays indoors. And the stack effect, which is warm air rising and escaping through the upper part of the house, pulls replacement air in through the lowest openings, sometimes including a flue that is supposed to be moving gases the other direction.

Carbon monoxide has no color, no smell, and no taste. Early symptoms are headache, dizziness, and nausea, which is why people so often blame a winter virus. The alarm on the wall is a better detector than you are.

What does a home inspector actually check on a furnace?

Here is what a standard inspection covers in a Fort Wayne or Warsaw home, and it is more than most buyers expect.

The operating cycle

We turn the thermostat up and watch the sequence: call for heat, inducer, ignition, burner, blower. We listen for delayed ignition, which sounds like a small boom a second or two after the gas lights, and we watch the flames. A steady blue flame is what we want. Flames that roll out toward the front of the cabinet, lift off the burners, or burn yellow point to a combustion or draft problem worth reporting.

The venting

This is where we find the most serious defects. On an older 80 percent efficiency furnace, we look at whether the flue pipe rises continuously toward the chimney, whether the joints are fastened, whether there is separation from wood framing, and whether the connector is rusted through at the draft hood. We regularly find flue pipes crushed or sloped downward by a duct installer working around them.

On a high efficiency condensing furnace, the vent is PVC. We check that the intake and exhaust terminate outside, that the joints are glued, and that the exhaust is not aimed at a window, a walkway, or a snow line where it can be blocked.

We report visible conditions and unsafe installations. We do not determine code compliance, which is a separate determination made by a building official.

The orphaned water heater

This comes up constantly in the older housing stock around Fort Wayne, Columbia City, and Decatur. When a homeowner upgrades an atmospheric furnace to a high efficiency model, the furnace stops using the masonry chimney. If the gas water heater is left venting into that now oversized chimney flue by itself, it often cannot establish draft. Combustion gas spills into the basement and moisture condenses inside the chimney, which destroys the liner over time.

Where conditions allow, we observe the draft hood for spillage during operation. A full combustion safety test under worst-case depressurization is a separate service performed by an HVAC or building performance contractor, and we will tell you when a house needs one.

Combustion air

A furnace in a tightly sealed mechanical room with no source of combustion air is being starved. We look for the openings and report their absence as a condition to be evaluated.

The gas piping and shutoff

We look at accessible connections, the sediment trap, the shutoff valve, and any flexible connector run through a wall or cabinet where it does not belong.

Ambient carbon monoxide and thermal imaging

Indiana Inspections carries a carbon monoxide meter and takes ambient readings in the living space and near the appliances. Our thermal imaging also picks up temperature patterns at flues and registers that are worth a second look. This goes beyond the minimum standard of practice, and not every inspection company does it. Ask before you book, whoever you hire.

Age and service history

The serial number tells us the manufacture date. A gas furnace generally runs 15 to 20 years. A 22-year-old unit in a house you are buying is a budget item whether or not it works the day we see it.

Can a home inspector tell if a heat exchanger is cracked?

No, and anyone who says otherwise is overselling the service. Most of the heat exchanger sits inside the cabinet, out of view, and a hairline crack that opens only when the metal is hot is not visible with a flashlight through a burner port.

What we can do is report the signs that point to a problem: flames that change shape when the blower starts, soot deposits, rust flaking inside the burner compartment, a rollout switch that has tripped, elevated carbon monoxide readings, or a cracked and rusted vent connector. Any of those goes in the report with a recommendation for evaluation by a licensed HVAC contractor, who can run a combustion analysis and scope the exchanger.

The honest version is that a home inspector finds the symptoms and a technician confirms the cause.

What furnace warning signs can a homeowner spot without tools?

• Soot or dark streaking around the furnace cabinet or the vent pipe

• Rust flakes on the floor under the flue connector

• A yellow or orange flame instead of blue on a natural gas burner

• A furnace that short cycles, turning on and off every few minutes

• Heavy moisture on windows in rooms with no obvious source

• A burning or metallic smell that persists past the first two runs of the season

• Headaches, dizziness, or fatigue that improve when you leave the house and return when you come back

The last one is the important one. If more than one person in the house feels it, or if a pet is affected, leave the house and call the fire department from outside.

Are carbon monoxide alarms required in Indiana homes?

No. Indiana amended the residential code so that carbon monoxide alarms are not required in one- and two-family dwellings or townhouses. The Indiana Department of Homeland Security amendment to Section R315 of the Indiana Residential Code states it plainly, and it is the reason we still inspect houses with a gas furnace, a gas water heater, an attached garage, and no carbon monoxide alarm anywhere in them.

Not required is not the same as not needed. Put an alarm on every level of the home, including the basement, and one outside each separate sleeping area. Check the manufacture date on the back of each unit, because the sensors expire on a schedule of roughly seven to ten years depending on the model, and a working test button does not mean a working sensor.

One more thing worth knowing. A standard residential alarm listed to UL 2034 is designed to sound at concentrations that pose an acute risk, not at the low levels that can cause ongoing symptoms across a whole winter. If someone in the house has persistent symptoms while the alarm stays silent, a low-level monitor listed to UL 2075 is a reasonable addition.

When should you schedule furnace service in Northeast Indiana?

Book the service call now. By the first sustained cold week in November, contractors across Fort Wayne, Warsaw, and Auburn are running behind, and the price of a Sunday night no-heat call is not the price of a Tuesday morning tune-up.

Change the filter, and keep changing it. Restricted airflow makes the furnace run hotter than designed, and heat stress is what damages heat exchangers over time. It is the cheapest item on this page and the one most often skipped.

Clear the area around the unit. Storage stacked against a furnace blocks combustion air and creates a clearance problem. If you have a high efficiency furnace, walk outside, find the PVC intake and exhaust terminals, and make sure February's snow line will not bury them.

Test every alarm in the house while you are thinking about it. The rest of the season's jobs are in our fall home maintenance checklist for Northeast Indiana.

Frequently asked questions

Does a home inspection include the furnace?

Yes. A standard home inspection in Indiana includes operating the furnace through a heating cycle and visually inspecting the burners, venting, combustion air provisions, accessible gas connections, and equipment age. It does not include dismantling the unit, testing combustion, or certifying the heat exchanger, all of which fall outside the standards of practice.

Can a home inspector tell if a heat exchanger is cracked?

No, not definitively. Most of a heat exchanger is not visible without disassembly. A home inspector reports the visible symptoms, such as flame disturbance, soot, rust flaking, a tripped rollout switch, or elevated carbon monoxide, and recommends evaluation by a licensed HVAC technician who can run a combustion analysis.

How long does a gas furnace last in Indiana?

Most gas furnaces run 15 to 20 years, with high efficiency condensing units often at the shorter end of that range. The manufacture date is encoded in the serial number on the data plate, and any inspector or technician can read it for you during a visit.

Where should carbon monoxide alarms be placed in a house?

Place a carbon monoxide alarm on every level of the home, including the basement, and one outside each separate sleeping area. Replace each unit at the interval printed on the housing, generally seven to ten years, since the sensor expires even when the test button still works.

What does a yellow furnace flame mean?

On a natural gas burner, a yellow or orange flame usually indicates incomplete combustion caused by a dirty burner, insufficient combustion air, or a draft problem. It should be evaluated by an HVAC technician before heating season, because incomplete combustion is what produces carbon monoxide in the first place.

Should you book a furnace inspection before winter?

A furnace that has run several winters without service is not a crisis, but October is the month to find out. If you are buying a home in Allen, Whitley, DeKalb, Kosciusko, Noble, Adams, or Steuben County this fall, our inspection covers the heating system in the detail described above and gives you the written documentation to negotiate with.

Schedule an inspection with Indiana Inspections, or call us and we will tell you honestly whether what you are seeing needs an inspector or an HVAC technician. We serve Fort Wayne, Columbia City, Auburn, Warsaw, Decatur, and the surrounding counties.