The Cracked Heat Exchanger Call, and How to Tell It Is Real

It is a real failure, it is the one fault on a furnace that genuinely cannot be patched, and it is also the finding most often used to sell equipment, which is why arguing about it gets you nowhere and asking how it was made gets you everywhere. Ask what was seen, how it was seen, and to be shown it. And know the difference between the two pieces of paper: a tag left on your furnace is that contractor refusing to operate the appliance, not an order from the city.

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What the part does, and why a crack in it is not something anybody patches

A gas furnace runs two air streams past each other and is built so that they never meet. On one side are the combustion gases from the burners, which go up the flue. On the other is the air the blower pushes through your ducts and into the rooms. The heat exchanger is the metal wall between them, and the whole safety case of the appliance rests on that wall being intact. New York's code agencies put the underlying chemistry plainly in their own 2025 code outreach bulletin: carbon monoxide is created when carbon from fuels such as gasoline, wood, coal, natural gas, propane, oil and methane burns incompletely, and heating and cooking equipment that burn fuel can be sources of it. A breach in the wall is a path from the exhaust side to the air you breathe, and the reason nobody welds it shut and hands the furnace back is that the part is the safety barrier itself. A patched barrier is a barrier nobody can stand behind, which is why a credible finding ends the conversation about repairing that component rather than starting one.

Ask how the finding was made, not whether it is true

Homeowners have been primed to disbelieve this call, and with reason, because it has been used to close system sales. But arguing about whether it is true is an argument you cannot win from the top of the basement stairs, and it is the wrong question anyway. The productive question is how the finding was made. Was the crack seen, or inferred? If seen, seen how: by eye with the burner assembly out, with a mirror and a light, with a camera passed into the exchanger? If inferred, inferred from what: a combustion analyzer reading, a change in the flame when the blower starts, something else? Can you be shown it, on a screen or in the metal? Can the readings be written down on the paperwork rather than described? None of that is hostile and none of it requires you to know anything technical. It converts an assertion into something you can carry to a second contractor and have examined. A technician confident in the finding will generally be pleased to show you, because it is the part of the job they can prove. Reluctance to show you anything is not proof of bad faith, but it is the point at which a second opinion stops being paranoia.

A tag on your furnace and a placard on your house are two different things

These get confused constantly and the difference decides who you call next. When a contractor shuts an appliance down on a safety finding and leaves a tag on it, that is that company's professional judgment and its refusal to operate the equipment or take responsibility for it. It is a judgment they are entitled to make, and one you are entitled to test by having somebody else look. The municipal process is a separate thing with a separate author. Under section 27-115 of the City of Syracuse Property Conservation Code, premises may be designated by the director as unfit for human habitation or dangerous to human life and placarded where, among other defects, the structure lacks heat, ventilation, sanitation or other facilities adequate to protect the health and safety of the occupants. That runs through a written notice and order which must contain the finding and a statement of intent to order the premises vacated and placarded if the notice is not complied with, premises ordered placarded must be vacated within the time the order specifies, and the placard may not be removed nor the premises reoccupied without written approval. So one is a company declining to relight your furnace, and the other is the city acting in writing with a chance to comply first. Knowing which is in front of you is the difference between calling a second contractor and calling the city.

The alarm on your wall is there because of a defective boiler

The reason to take a combustion finding seriously is not that a salesperson said so. It is a matter of public record. The New York State Department of Health states that Amanda's Law was passed in 2009 and was named for a sixteen year old who died of carbon monoxide poisoning from a leak in a defective boiler. The Department of State records it as Chapter 367 of the Laws of 2009, amending Executive Law section 378(5-a), and describes exactly what it changed: before it, the codes required carbon monoxide alarms only in one and two family dwellings, townhouses and condominium or cooperative dwelling accommodations constructed or offered for sale after July 30, 2002, and in multiple dwellings after August 9, 2005. The rule implementing it amended the Residential Code and the Fire Code of New York State to require alarms in all of those dwelling types without regard to the date of construction or sale. It reached backwards into existing homes deliberately, which matters in a city where most of the housing predates the codes entirely. And the statutory trigger is broad: Executive Law 378(5-a) attaches the requirement where a dwelling has appliances that may emit carbon monoxide, or an attached garage.

Your alarm is probably not in the room the code cares most about

Most people believe the requirement is one alarm on the floor where the bedrooms are, and the code text goes further than that. Section 705 of the 2020 Property Maintenance Code of New York State requires carbon monoxide alarms and detection to be installed and maintained in accordance with Section 915 of the Fire Code of New York State, and Section 915.1 states that new and existing residential and commercial buildings shall be provided with carbon monoxide detection and notification. Section 915.3.1 then requires detection in all rooms, occupiable spaces, dwelling units, sleeping areas and sleeping units that contain a fuel-burning appliance, which in this metro usually means the basement with the furnace or boiler standing in it. Section 915.3 adds where not to put one, and it rules out two places people choose for convenience: detectors must be installed in locations that avoid dead air spaces, turbulent air spaces, fresh air returns, open windows, HVAC ducts, closed doors and other obstructions that could keep the gas from reaching the sensor. Where the code and the manufacturer's instructions disagree on location, the more restrictive one governs. If you take one action away from this page, walking downstairs to see whether there is an alarm in the room with the appliance is a good candidate.

Check the manufacture date on the back, not the battery

An alarm that cannot sound is worse than no alarm, because it is also reassuring. The Fire Code of New York State requires carbon monoxide alarms to take primary power from the building wiring where that wiring is served from a commercial source, with battery backup and permanent wiring carrying no disconnecting switch other than the overcurrent protection. The exceptions are the part that applies to most houses here: an alarm powered by a ten year battery is permitted in residential and commercial buildings without commercial power, and in existing residential and commercial buildings unless the Uniform Code requires otherwise. Alarms must be listed and labeled as complying with UL 2034 or CAN/CSA 6.19, and a combination carbon monoxide and smoke alarm is an acceptable alternative. So in an existing Syracuse house a sealed ten year unit is generally acceptable, which makes the useful check the date printed on the back of the housing rather than the test button on the front. A unit past its ten year life is a unit that may not sound whatever the button does, and the state's own advice is to check alarms twice a year and to schedule annual maintenance on furnaces and other heat sources.

The state's test is a pattern, not a list of symptoms

This is the part of the subject where careless writing does real harm, so here is what the health department actually publishes and nothing beyond it. The New York State Department of Health describes carbon monoxide as a colorless, odorless gas that can kill before a person is aware it is present, and states that carbon monoxide exposure is the leading cause of death due to poisoning in the United States. Its guidance for suspecting it is a pattern rather than a symptom: where symptoms occur or worsen soon after a fuel-burning device is turned on, where more than one person in the area becomes ill at the same time, or where those who are ill feel better after leaving the area. Note what that is not. It is not a checklist of feelings to match yourself against, no single symptom tells you the gas is present, and this page is not going to give you an exposure number to compare a reading against, because that is a question for a doctor and for the fire department rather than for a website. If an alarm is sounding, the answer is not on any web page: get everyone out into fresh air immediately and contact the fire department and the gas company or a heating contractor.

Why a furnace that behaved for twenty years started burning badly after the basement was finished

Combustion problems are not always the appliance, and this is the cause most often missed because the work that caused it happened somewhere else in the house. A furnace has to have air to burn. Section 27-54(h) of the City of Syracuse Property Conservation Code requires direct-fired heat producing equipment and the enclosure it sits in to be provided with a supply of air adequate to replenish the air consumed by complete combustion at the rated gross output, and to ventilate the enclosure, supplied by openings to the exterior or by fixed openings into interior spaces that themselves open to the exterior. Section 27-54(i) deals with the other end of it, requiring solid and liquid fuel equipment to be connected to suitable chimneys or flues rather than gas vents, prohibiting unvented liquid fuel heaters, and requiring gas-fired equipment to be connected to a suitable chimney, flue or gas vent where discharging combustion products into the space would be a hazard. That is the City's code and it governs city addresses, but the physics is identical in every town in the county. Finishing and sealing a basement, closing off a vent opening, or adding a powerful kitchen or bathroom exhaust fan can change the air available to an appliance that was fine for decades. If a combustion complaint appeared after other work was done, the air supply is worth investigating before the furnace is condemned.

A quarter of city homes cannot produce this from the heating at all

Not every house in this conversation is even in it, and it is worth saying because the fear does not sort itself by fuel type. The American Community Survey 2020-2024 estimates report that of 59,816 occupied housing units in the city of Syracuse, 41,477 are heated with utility gas, which is 69.3 percent, and 15,088 with electricity, 25.2 percent, with about one percent each on bottled gas and on fuel oil or kerosene. If your heat is electric, with no flame, no flue and no exhaust, the heating system is not a carbon monoxide source, and a burning smell from it is an electrical question rather than a combustion one, which is a completely different call to make. What that does not do is get the house out of the alarm requirement, because Executive Law 378(5-a) attaches wherever there are appliances that may emit carbon monoxide or an attached garage, and a gas range, a gas water heater or a car parked under the house all qualify on their own.

The far more common fault that looks like this one, and the second opinion that is worth having

Before assuming the worst, separate this from the thing that looks similar and is not. A furnace that lights, runs for a few seconds and shuts down, repeatedly, is usually a flame safeguard doing its job, and New York requires that device: section G2431.2 of the Residential Code of New York State requires every fuel gas space heating appliance in a home to shut off the fuel supply to the main burner when the flame or pilot light is extinguished. That is a cleaning, not a condemnation, and it is on the list of cheap causes worth ruling out before anybody gets near the expensive diagnosis. Where the finding really is the exchanger, a second opinion on a shut down appliance is reasonable and easy to arrange, and the only thing worth being clear about is what a second opinion is not. No contractor worth having will put a tagged appliance back into service over the telephone, or override another company's safety decision to win the work, and one offering to has answered the question about whose judgment to trust. Tell us what you were told, what you were shown, and which town you are in, and we will connect you with a licensed, insured contractor to look at the same furnace, with no obligation.