Covered as a system, decided by one part
Heating is a covered item in nearly every home service contract, usually described as all parts and components of the permanently installed heating system up to five tons. Whether a claim is paid almost always comes down to one component the contract covers and no inspection standard requires anyone to look at: the heat exchanger.
The distinction governing both risk and coverage is the fuel. A gas or oil furnace burns fuel inside a sealed metal heat exchanger; house air blows over the outside of that metal while combustion gases stay inside and leave through the flue. The heat exchanger is the only barrier between the two. An electric furnace or air handler uses resistance elements - no combustion, no heat exchanger, no carbon monoxide, no flue. A heat pump runs an air conditioner in reverse, falling back on electric strip heat below its balance point; one with a failed reversing valve still heats on strip heat, which is why that failure goes unnoticed until a startling utility bill arrives.
The heat exchanger, and the hole in every standard of practice
Every inspection standard reviewed excludes the heat exchanger from required inspection - not by omission, but by name:
- InterNACHI section 3.4: the inspector is not required to "inspect, measure, or evaluate the interior of flues or chimneys, fire chambers, heat exchangers, combustion air systems, fresh-air intakes, makeup air, humidifiers, electronic air filters, geothermal or solar heating systems."
- ASHI section 8.2: the inspector is not required to inspect "interiors of vent systems, flues, and chimneys that are not readily accessible, heat exchangers, humidifiers and dehumidifiers."
- Texas rule 22 TAC 535.230(d): the inspector need not verify the integrity of the heat exchanger.
InterNACHI's gas furnace checklist notes that removing cabinet panels is beyond the scope of a visual-only home inspection. The component is partly obscured by burners and the blower even when panels come off, and often cannot be assessed without a combustion analyzer or camera scope.
The stakes are why the exclusion deserves stating plainly. A crack admits combustion products, including carbon monoxide, into the supply air the blower sends to bedrooms. CPSC's estimates of non-fire carbon monoxide deaths report an estimated 250 for 2019, more than any other year in that report, of which an estimated 69, or 28 percent, involved heating systems.
The single most safety-critical component in a gas furnace is the one no general home inspection is required to evaluate. If the report says the furnace operated, that is a statement about operation. It is not a statement about the heat exchanger and was never intended to be one.
What a recommendation for HVAC evaluation actually does
"Recommend evaluation by a licensed HVAC contractor" appears in an enormous number of reports and is misread in both directions - as an inspector hedging, or as a problem already handled. It is neither. It is the designed output of a visual standard, and it does three things.
It ends the inspector's duty, correctly
The standards require the inspector to report. InterNACHI requires reporting as needing correction a heating system that did not operate or was inaccessible; Texas requires reporting specified conditions as deficient. None require diagnosing cause, quantifying cost or determining remaining life. Referral is also the inspector's principal liability defense - a professional liability insurer for home inspectors reports that over 80 percent of the claims it receives are meritless.
By itself it obligates the seller to nothing
A home inspection report is a report to the party who ordered it. Whether anything must happen next is governed by the purchase contract's inspection contingency, not by the report. If that period expires without a written request, the finding carries no contractual force and the buyer owns a well-documented problem with no remedy. It does create seller knowledge going forward: an unremedied recommendation is a documented condition most state seller-disclosure regimes treat as material and known.
It is a warranty problem, not a warranty solution
A recommendation for evaluation is close to a written record of a pre-existing condition. One agreement states that "Known or unknown pre-existing conditions are not covered"; another excludes breakdowns existing before the plan start that were "reasonably detectable by you." Buying a service contract after an inspector flags the furnace does not convert the flagged item into a covered one.
A referral is a task with a deadline, not a disclosure. Obtain the specialist evaluation inside the inspection contingency window, in writing, with a scope that names the heat exchanger explicitly.
What the contract grants, and the exclusion list that outruns it
The heating grant is broad. One national agreement covers all parts and components of permanently installed heating systems up to five tons across forced air gas, electric and oil, geothermal, package units, heat pumps and mini-splits. Another covers heating "if providing the primary source of heat in dwelling."
Then the exclusions. One buyer-seller form excludes, in a single run: chimneys, flues and liners; cleaning and re-lighting of pilots; concrete-encased or inaccessible ductwork or radiant heating coils; fossil and dual fuel control systems; dampers; asbestos-insulated ductwork or piping; electric baseboard heat unless it is the primary system; filters of every type; fireplaces and their gas lines; free-standing and portable heating units; fuel storage tanks and lines; gas log systems; humidifiers; maintenance and cleaning; radiant heating built into walls, floors or ceilings; registers and grills; secondary units; and solar heating devices. Other forms add wood, pellet and grain stoves - excluded in at least two contracts even if they are the only source of heating - plus cable heat and auxiliary space heaters.
Secondary units and non-primary heat. Several contracts cover the heating system only where it provides the primary source of heat. A second furnace serving a finished basement, an addition or a converted attic may be entirely uncovered while the main unit is fully covered, and nothing on the covered-item list says so.
Caps, and the flue nobody budgeted for
Heating draws on the same per-covered-item limits as the rest of the contract - $5,000 per covered item in one 2024 national form, $3,000 per covered item per 12-month period in another, with hot water and steam circulating systems dropped to $1,500 in the first. Where that clause absorbs access and diagnosis, diagnostic visits come out of the same allowance as the equipment.
The exclusion that most often converts a covered repair into an uncovered project is chimneys, flues and liners. The sequence is predictable: an older furnace is condemned for a cracked heat exchanger, the replacement is a condensing unit venting through PVC, and the existing masonry chimney or B-vent is then oversized or non-compliant - especially where a water heater shared that flue and is now orphaned on it. The correction is required to make the installation legal, and it sits outside coverage. Combustion air is the parallel case: ASHI relieves the inspector of determining the adequacy of combustion air components, so a marginal furnace closet may be documented by nobody until a contractor arrives with a permit application (ASHI Standard of Practice).
How furnaces fail, and how long they last
The InterNACHI chart gives 15 to 25 years for a furnace, 10 to 15 for a heat exchanger and 10 or more for a burner. ASHRAE's survey median for a residential furnace, packaged condensing unit or heat pump is 31.0 years, from a population weighted toward commercial buildings. Note the tension inside InterNACHI's own chart: the heat exchanger is rated shorter than the furnace containing it, which fairly reflects reality, since that failure usually ends a furnace's life.
- Low airflow causing overheating. InterNACHI states it directly: "One of the most common causes of heat exchanger failure is overheating due to low air flow." The causes are mundane - a clogged filter, closed registers, crushed return ducts - connecting the most expensive failure to the least-inspected system in the house.
- Short cycling from an oversized furnace, which multiplies thermal expansion cycles and fatigues metal faster than run hours alone suggest.
- Condensate corrosion in mid-efficiency units that condense when they were never designed to.
- Venting and back-drafting problems, simultaneously a combustion safety issue and a corrosion accelerant.
The first item is why the maintenance-records demand works so well as a denial mechanism. Contracts cover failures from normal wear and tear but exclude malfunction from misuse, abuse, neglect or physical damage, and a cracked heat exchanger caused by overheating behind a filter nobody changed is textbook neglect. A state consumer-protection action has alleged that demanding multiple years of maintenance records before approving coverage functioned as a denial tactic.
Once the diagnosis lands, the economics are lopsided. A cracked heat exchanger inside its manufacturer warranty may yield a free part but never free labor, and outside that warranty the labor on an old furnace commonly approaches the cost of a new one - which is why "evaluated and condemned" is a common outcome. Be skeptical in both directions: contractors have an incentive to condemn, while a furnace that runs is not thereby sound, since a crack can be closed cold and open at operating temperature. The stakes justify paying for camera evidence and a combustion analysis rather than accepting a verbal finding.
What a buyer does, and by when
The heating system rewards a short list of actions during the inspection or option period, while a remedy exists.
- Read what the report says. "Furnace operated at time of inspection" is not a heat exchanger finding.
- Convert any referral into a scoped evaluation with a date. Name the heat exchanger and get it inside the contingency window in writing.
- Establish whether the unit is the primary heat source, since secondary units are excluded outright in several contracts.
- Collect the maintenance history from the seller, since service records are what the denial mechanism runs on.
- Ask what the flue serves and whether it is shared, because chimneys, flues and liners are excluded.
- Install carbon monoxide alarms before the first heating season, particularly on a summer purchase where the furnace ran only briefly (CPSC carbon monoxide fatality estimates).
One finding confuses buyers every year: in Texas an inspector must report as deficient burners or heating elements "less than 18 inches above the lowest garage floor elevation." A garage furnace on a raised platform is not evidence of past flooding - it is the code response to the risk of igniting heavier-than-air fuel vapors at floor level, and its absence is the reportable condition.
Frequently Asked Questions
Does a home inspector check the heat exchanger?
No standard reviewed requires it. InterNACHI section 3.4 expressly relieves the inspector of inspecting, measuring or evaluating heat exchangers; ASHI section 8.2 lists them among components the inspector need not inspect; and the Texas rule states the inspector is not required to verify heat exchanger integrity. The component sits inside a closed cabinet, and removing panels is described by InterNACHI as beyond the scope of a visual-only inspection. A meaningful assessment requires a licensed HVAC contractor with a combustion analyzer, a camera scope, or both.
What does a recommendation for evaluation by a licensed HVAC contractor mean?
It means the inspector observed something the standard requires reporting but does not require diagnosing, and has referred the question to a trade specialist. It is the designed endpoint of a visual inspection, not an evasion. It also means a deadline is running: the report obligates the seller to nothing, and whether anything happens next is governed by the purchase contract's inspection contingency. If that period expires without a written request the finding carries no contractual force, and buying a service contract afterward will not help.
Will a home warranty pay for a cracked heat exchanger?
A heat exchanger in the primary heating system is normally a covered component, so the answer turns on the exclusions rather than the grant. Contracts cover failures from normal wear and tear but exclude malfunction from misuse, abuse, neglect or physical damage, and the most common cause of heat exchanger failure is overheating from low airflow - a clogged filter or restricted ducts, which reads as neglect. Two limits apply even on an approved claim: the per-covered-item cap governs the payout, and chimneys, flues and liners are excluded, so venting corrections fall outside coverage.
Is a second furnace in the basement or an addition covered?
Often not. Several contracts cover the heating system only where it provides the primary source of heat in the dwelling, and one buyer-seller form separately excludes "secondary units" by name. A house with a main furnace plus a second unit for a finished basement can have one fully covered system and one entirely uncovered one. Related exclusions catch the same situation from other directions: electric baseboard unless primary, space heaters, and wood, pellet and grain stoves - excluded even where they are the only source of heat.
How long does a furnace last?
The InterNACHI life expectancy chart gives 15 to 25 years for a furnace, with the heat exchanger rated separately at 10 to 15 years. ASHRAE's survey database reports a much longer median of 31.0 years for a residential furnace, packaged condensing unit or heat pump, from a population skewed toward commercial buildings. The shorter heat exchanger figure is the meaningful one, because that failure usually ends the furnace's service life rather than general wear.
Does a home warranty cover the chimney or flue?
Chimneys, flues and liners are excluded in the contracts reviewed, and the exclusion has more bite than it first appears. Replacing an older furnace with a higher-efficiency unit frequently leaves the existing vent oversized or improperly lined, and the correction is required for the installation to be legal. The problem compounds where a water heater shared the flue and is left orphaned on a chimney sized for two appliances.