Granted by one clause, removed by the next
Ductwork is the clearest case of coverage that exists in the grant and disappears in the qualifier. The typical contract covers ducts running from the heating or cooling unit to the point of attachment at the registers, then defines away any part it cannot easily reach. Whether a duct failure is covered rarely depends on what broke - it depends on where the broken part is.
Ducts are the conduits that deliver and remove air: supply ducts carrying conditioned air out, return ducts bringing house air back, plenums where the runs originate, dampers that balance them, and registers and grilles at the room end. They may be sheet metal, ductboard or flex, and they run through attics, crawlspaces, joist bays, sealed chases, or cast into slabs.
Ductwork holds an unusual triple position: the longest-lived item on the standard life expectancy chart, the least-inspected system in the house, and the one most likely to be excluded on accessibility grounds. Those facts are connected - what rarely fails outright gets ignored.
Where the covered run starts and where it stops
The grant language is consistent and precise about its endpoints. One buyer-seller agreement covers "accessible ductwork from the air conditioning unit to the point of attachment at registers/grills"; another covers "Ducts (unless collapsed or clogged) from unit to point of attachment at registers or grills." Coverage stops at the register, and the boundary differs by contract.
| Component | How contracts treat it |
|---|---|
| Duct run, unit to register | Covered in all four forms reviewed, subject to accessibility |
| Registers and grilles | Excluded by name in two forms; expressly included by one national form |
| Dampers | Excluded in two forms; covered, including damper-only controls, in one |
| Whether ductwork is in the plan at all | A separate covered item with a $5,000 limit in one 2024 form; a premium-tier or optional add-on in another |
That last row is the one buyers miss most often. Ductwork being part of the HVAC system does not make it part of the plan: in at least one structure it sits in the upper tier or is sold as an add-on, so a base-plan holder with a failed duct has no covered item to claim against.
What not accessible means in a contract
In conversation, inaccessible means hard to get to. In a home service contract it is a defined term, broad enough to capture most of the duct in a house:
One agreement defines inaccessible ductwork as "ductwork that is not exposed and cannot readily be accessed for replacement or repair due to design and installation obstacles such as, but not limited to, permanent partitions, chimneys, etc., and ductwork embedded in floors, walls or ceilings." Note the test: not exposed, not reachable for repair or replacement rather than for viewing, and obstructed by the building's own design.
Apply it honestly to a real house. Duct in an open attic or unfinished basement is exposed. Duct in a sealed chase, behind a soffit, inside a finished wall, above a finished ceiling or under a slab is not - and none of that is unusual construction. Access sub-caps apply on top: contracts variously provide access through one layer of unobstructed drywall returned only to a rough finish, cap concrete access at $1,000, or pay up to $500 to reach encased items. A few hundred dollars of demolition, restored to bare drywall, is the practical shape of the remedy.
Slab ducts, collapsed ducts, clogged ducts
Three fact patterns account for most denied duct claims, all knowable before closing:
Ducts in or below a concrete slab
Ducts cast into or run beneath a slab are common in mid-century single-story construction in the South and Southwest, and are the worst case here. One form excludes concrete-encased or inaccessible ductwork outright; another caps coverage for "DIAGNOSIS, ACCESS, REPAIR OR REPLACEMENT OF DUCTWORK LOCATED IN OR BELOW A CONCRETE SLAB" at $500; a third pays up to $500 to access concrete-covered items. The realistic repair for a failed under-slab system is abandonment in place and re-running the distribution overhead, with new drops, returns and ceiling registers throughout the house. Against that scope, a $500 access allowance is not a remedy.
Collapsed and clogged
One contract covers ducts "unless collapsed or clogged" and separately excludes collapsed and clogged ductwork by name. Collapse is the characteristic failure of flexible duct - crushed by attic storage, kinked at a bend, or sagging until airflow drops - and clogging means a run full of debris or rodent nesting. Those are the two reasons homeowners call about ducts, and that parenthetical removes both.
Read the exclusions together and the shape of duct coverage is clear: the contract pays for leaks and breaks in accessible runs and declines the conditions behind most service calls. On a single-story slab house, establish where the ducts run before evaluating any contract.
Asbestos ends the claim and starts a different problem
Older houses carry a risk that converts a routine duct repair into a regulated project. One buyer-seller form excludes asbestos-insulated ductwork or piping; another excludes "DUCTWORK WHERE ASBESTOS IS PRESENT" and adds that the company will not perform service involving hazardous or toxic materials.
The sequence is unpleasant. A technician opens a basement ceiling in a 1950s house, finds corrugated paper wrap on the round ducts or white cloth tape at the joints, and stops. The claim is over, and the homeowner now owns a suspected asbestos condition that has been partially disturbed.
EPA's guidance identifies pipe, furnace and boiler insulation among asbestos-containing materials in homes, and its core instruction is to leave undamaged material alone: material in good condition that is not disturbed will not release fibers. Where it is damaged or renovation is planned, removal should be done by an accredited asbestos professional, and EPA warns that improper removal may increase exposure (EPA, protect your family from exposures to asbestos). A general home inspector is neither required nor qualified to identify these materials, so suspected duct wrap should be assessed by a licensed asbestos inspector.
Why the inspection will not find it either
Ductwork is the one HVAC component where the inspection standards are thinner than the contract. The InterNACHI Residential Standards of Practice contain no ductwork section at all: duct defects surface, if at all, under the heating and cooling sections' duty to report a system that did not operate. There is no required duct inspection, airflow measurement or leakage test.
ASHI does require inspection of "distribution systems" under its heating and air conditioning sections, then withdraws the substance: sections 8.2 and 9.2 exclude determining heat and cooling supply adequacy and distribution balance, and section 11.2 provides that the inspector is not required to disturb insulation - exactly what seeing the duct underneath would require. Section 13.2 excludes the condition of components that are not readily accessible, defined in section 14 as available for visual inspection without dismantling or destructive measures. That describes nearly every duct run in a finished wall, chase or slab (ASHI Standard of Practice).
Texas is the most demanding of the three, requiring reports of damaged duct systems, absence of air flow at accessible supply registers, and gas piping and sewer vents concealed in ducts, plenums and chases. Note the word accessible again, limiting even the airflow check. Outside every standard, and requiring a specialist: leakage testing, airflow measurement, Manual J and D sizing calculations, camera inspection and asbestos identification.
Leakage: the dominant defect that is not a breakdown
The most consequential thing wrong with the average duct system is not a break. It is leakage: invisible, unmeasured and uncovered. ENERGY STAR states that about 20 to 30 percent of the air moving through a typical duct system is lost through leaks, holes and poor connections - a figure published without an underlying study citation, and one to attribute to ENERGY STAR rather than treat as an independent finding.
Leaky but intact ductwork is not a "breakdown." No home service contract pays to seal ducts, because nothing has failed in the contractual sense; no inspection standard requires measuring it; and the owner pays for it every month in the utility bill instead. It is the clearest example of a real, expensive defect sitting in the gap between two documents that each assume the other covers it.
Code supplies a benchmark for new construction. Under the 2021 IECC as adopted in Washington, total duct leakage at rough-in must be no more than 4.0 cfm per 100 square feet, with a relaxed 8.0 cfm limit where all ducts and air handlers sit within the thermal envelope (WAC 51-11R-40320). Sources disagree on whether the model code retains that exception, so treat it as unresolved; the testing requirement and the 4.0 and 8.0 figures are consistent. A thirty-year-old house has never been tested against any of them. On method, ENERGY STAR is blunt: seal with mastic sealant or metal tape, and "Never use duct tape, as it is not long-lasting."
How ducts age, and what to check before the window closes
The InterNACHI chart rates ducting at 60 to 100 years and registers at 25 - the longest life expectancy of any HVAC component. That is precisely why ducts get ignored: they rarely fail, they quietly underperform for decades. Flexible duct is the exception, degraded by ultraviolet exposure, attic heat, rodent damage and compression at bends, and a crushed flex run restricts airflow enough to overheat a furnace heat exchanger - the same chain InterNACHI identifies when it notes that one of the most common causes of heat exchanger failure is overheating due to low airflow. A duct problem nobody was required to inspect can destroy the most expensive component in the heating system, and the claim will be assessed as a maintenance failure.
- Where the ducts run - attic, crawlspace, interior chases or under the slab. Ask directly on a single-story slab house.
- What they are made of - sheet metal, ductboard or flex, and in an older house whether any wrap or joint tape warrants an asbestos assessment.
- Whether air actually arrives. Absence of air flow at accessible supply registers is a reportable deficiency in Texas and a fair question anywhere.
- Whether ductwork is in the plan tier at all, and how that contract defines accessibility.
The throughline is the same as everywhere else on this site: cheap questions before the contingency period closes, expensive discoveries afterward. A duct run nobody looked at, in a place no contract will pay to reach, is not a defect anyone will help with once the window expires.
Frequently Asked Questions
Is ductwork covered by a home warranty?
Conditionally, and in some structures only if it was purchased. The typical grant covers ducts from the heating or cooling unit to the point of attachment at registers or grilles, subject to the run being accessible. One national form treats ductwork as its own covered item with a $5,000 limit and covers leaks and breaks including plenums, dampers, registers and grills; another places it in a premium plan or optional add-on. Because coverage varies more than for most items, ductwork is worth confirming line by line.
What does inaccessible ductwork mean in a home warranty?
It is a defined contract term, not a judgment call made at claim time. One agreement defines it as ductwork that is not exposed and cannot readily be accessed for replacement or repair due to design and installation obstacles such as permanent partitions or chimneys, and ductwork embedded in floors, walls or ceilings. The test turns on access for repair rather than for viewing, which is why so much of a normal house qualifies: duct in an open attic is generally accessible, duct in a sealed chase, a finished wall or under a slab generally is not.
Are ducts under a concrete slab covered?
They are the least covered item in this subject. One form excludes concrete-encased or inaccessible ductwork outright; another caps diagnosis, access, repair or replacement of ductwork located in or below a concrete slab at $500; a third pays up to $500 to access concrete-covered or encased items. The realistic fix for a failed under-slab system is abandoning it and re-running the distribution overhead, so a $500 allowance covers access, not repair.
Does a home warranty pay for duct cleaning or duct sealing?
Neither, and the two are frequently confused. Cleaning is excluded as maintenance, and clogged ductwork is separately excluded by name in at least one contract. Sealing is not covered because nothing has broken: a leaky but intact system has not suffered a breakdown in the contractual sense. Sealing is nonetheless the intervention that recovers real money, given ENERGY STAR's estimate that about 20 to 30 percent of the air moving through a typical system is lost, and ENERGY STAR recommends mastic sealant or metal tape while warning against duct tape.
Does a home inspector check the ductwork?
Barely, and far less than buyers expect. The InterNACHI Residential Standards of Practice contain no ductwork section at all. ASHI requires inspecting distribution systems but excludes determining heat and cooling supply adequacy and distribution balance, and provides that the inspector need not disturb insulation - which is what seeing a buried duct would require. Texas requires reports of damaged duct systems and absence of air flow at accessible supply registers, but leakage testing and duct sizing sit outside every standard reviewed.
What happens if asbestos is found on the ducts?
The service contract stops. One form excludes asbestos-insulated ductwork or piping; another excludes ductwork where asbestos is present and states the company will not perform service involving hazardous or toxic materials. The claim ends and the condition remains, now potentially disturbed. EPA's guidance is to leave undamaged asbestos-containing material alone, since material in good condition that is not disturbed will not release fibers, and to use an accredited professional where it is damaged.