Heat Exchanger Repair Draper UT | Draper Heating & Air

Heat Exchanger Repair & Inspection in Draper, Utah

A cracked heat exchanger is a legitimate furnace failure — a structural breach in the steel or stainless steel wall that separates the combustion products in the flue gas circuit from the conditioned air in the supply air circuit. When that wall fails, the flue gas and the conditioned air mix. Carbon monoxide enters the living space through the supply air distribution system. In a tightly sealed winter home in Draper, Sandy, or SunCrest, that CO accumulates.

A cracked heat exchanger is also the most commonly misdiagnosed furnace condition in the south Salt Lake Valley — condemned without visual evidence by contractors using diagnostic methods that cannot confirm a crack, to homeowners who have no easy way to verify the claim. We have overturned more than 14 competitor condemnation quotes in the past three heating seasons in our service area using borescope inspection and combustion analysis. In some of those cases the heat exchanger was fine. In others, the heat exchanger had a real problem that the first contractor’s method would not have definitively identified even if the conclusion had been correct.

This page explains what we do to confirm or rule out a heat exchanger problem, what our findings mean for your family’s safety and your decision-making, and when a cracked heat exchanger genuinely requires furnace replacement versus other options.

What the Heat Exchanger Does

The heat exchanger is the core thermal transfer component of a gas furnace. In a typical upflow furnace, the primary heat exchanger consists of a series of folded steel or stainless steel cells arranged around the burner compartment. Combustion gases flow through the inside of these cells from the burner section to the inducer. Conditioned air from the return duct flows across the outside of the cells, absorbing the heat conducted through the cell walls before continuing into the supply plenum and distribution system.

This two-circuit arrangement is the furnace’s fundamental safety feature: the combustion products (CO, CO₂, NOx, water vapor) stay inside the heat exchanger cells and exit through the flue vent, while the conditioned air that reaches occupants never contacts the combustion gases directly. When the heat exchanger wall fails — through cracking, perforation, or stress fracture — that separation is compromised.

90%+ AFUE condensing furnaces have a secondary heat exchanger in addition to the primary exchanger. The secondary exchanger extracts additional heat from the flue gases by cooling them below the dew point, condensing water vapor out of the exhaust stream (producing the condensate that drains away). Secondary heat exchanger failures are less common than primary failures but occur on condensing units in the 12–18-year age range, particularly in the south Salt Lake Valley where hard condensate water from Wasatch snowmelt (15–25 grains per gallon) accelerates scale buildup on the secondary exchanger’s internal surface.

How Heat Exchanger Failures Occur

Thermal Fatigue

The most common cause of heat exchanger failure in residential furnaces. Each time the furnace starts, the heat exchanger metal expands rapidly as it heats to combustion temperatures (600–1,200°F at the primary exchanger surface). Each time the burner cycles off, it contracts. Over 15–20 years of cycling — approximately 100,000–150,000 start-stop cycles over the furnace’s life at typical south Salt Lake Valley cycling rates — this thermal stress accumulates and eventually cracks the metal at stress concentration points: weld seams, bend radii, and areas where the cell geometry changes cross-section.

Thermal fatigue is accelerated in two specific conditions common in our service area:

  • Altitude derate skipped: A furnace running at sea-level gas valve settings at SunCrest or Traverse Ridge elevation runs with excess fuel relative to available oxygen. The rich-burn combustion produces higher-than-designed flame temperatures at the primary heat exchanger surface. Over 5–10 seasons, the elevated combustion temperature accelerates thermal fatigue in the heat exchanger cells significantly compared to a correctly derated installation at the same elevation.
  • High static pressure reducing airflow: A furnace operating with restricted supply airflow (oversized MERV filter, collapsed flex duct, undersized return) runs at elevated temperature rise — the supply air absorbs the designed heat input over less airflow volume, resulting in higher air temperatures. The heat exchanger metal runs hotter than design intent. Over years of operation above the rated temperature rise, this accelerates thermal fatigue at the cell walls.

Corrosion

Condensation forms on 80% AFUE (non-condensing) furnace heat exchangers during cold-start cycles when outdoor temperatures are below approximately 40°F — the flue gas cools below its dew point in the first few minutes of operation before the heat exchanger reaches steady-state temperature. This condensate is slightly acidic (from dissolved CO₂ and NOx in the flue gas) and can cause pitting corrosion on the heat exchanger surface over years of seasonal cold-start exposure. The outlet end of the heat exchanger cells, where the exhaust gases are coolest, is the most common corrosion site.

Manufacturing Defects

Some heat exchanger failures in systems under 8 years old are attributable to manufacturing defects: incorrect weld joint geometry, substandard steel grade, or dimensional tolerances that create stress concentrations not present in the design specification. Manufacturer warranty claims (most major manufacturers offer 20-year limited heat exchanger warranties on residential equipment) cover manufacturing-defect failures if the furnace was registered within the required window and annual maintenance was documented. We file heat exchanger warranty claims on behalf of customers whose equipment meets the coverage criteria.

How We Diagnose Heat Exchanger Failures

What We Do Not Use: The Flame Deflection Test

The flame deflection test (passing a hand, a tissue paper, or a lighted match near the heat exchanger with the burner running and the blower running) is a historical screening method that detects airflow through a heat exchanger breach by observing flame or smoke disturbance. It is not a diagnostic confirmation of a cracked heat exchanger. Blower-induced pressure differentials, duct leak-induced air currents, and the general airflow patterns in the furnace cabinet can produce flame deflection near the heat exchanger without any breach in the cell walls. A positive flame deflection test confirms there is airflow near the heat exchanger. It does not confirm where the airflow originates or whether the heat exchanger wall is breached. We do not use flame deflection tests to condemn furnaces, and we do not accept “the flame moved” as documented evidence of a cracked heat exchanger from a competitor’s report.

Combustion Analysis — The Initial Indicator

A Testo 320 Basic flue gas combustion analysis performed at steady-state operation provides the initial indicator of heat exchanger integrity:

  • CO air-free in the flue gas above the altitude-corrected target range is a combustion problem. It may indicate a cracked heat exchanger allowing return air dilution into the combustion gas circuit, but it may also indicate an altitude derate error, burner port restriction, or a gas valve manifold pressure problem. CO in the flue gas alone does not confirm a heat exchanger crack.
  • Ambient CO measured at the return air grille is the more clinically meaningful finding. If CO is present in the air being drawn into the return system at concentrations above background levels (0–2 ppm in a well-maintained home), it suggests a path from the flue gas circuit to the conditioned air circuit. This is the finding that triggers a full borescope inspection immediately.

Borescope Inspection — The Confirmation

Borescope inspection of the heat exchanger is the definitive diagnostic step. We use a flexible fiber-optic borescope (5.5mm probe diameter, with LED illumination and a high-resolution display or tablet camera attachment) inserted through the burner access panel into each heat exchanger cell in sequence.

The inspection protocol:

  1. Burners removed (on atmospheric-burner models) or primary heat exchanger access opened (on induced-draft models) to expose the inlet end of each cell
  2. Borescope probe inserted into each cell and advanced to the full visible length of the cell — typically 12–18 inches per cell on residential furnaces
  3. Systematic inspection of each cell at the inlet end, mid-section, and outlet end, noting: visible cracks, perforations, dimples (stress concentration precursors to cracking), overfire discoloration indicating rich-burn combustion, and scale buildup from condensate on non-condensing furnaces
  4. Documentation with still photos at any finding and video recording where findings are ambiguous or require a second opinion review
  5. CO measurement in ambient return air both before and after the borescope inspection, confirming whether the CO presence correlates with operational findings

Each cell is inspected individually. A heat exchanger with four cells requires four separate probe insertions. A heat exchanger with six cells requires six. We do not extrapolate from two cells to the full heat exchanger — cracking does not always occur uniformly, and a cell that looks clean at the inlet end may have a crack at the outlet end not visible from the burner access opening without probe advancement.

Finding Classifications

  • Clean inspection, no findings: All cells free of visible cracks, perforations, or concerning discoloration. Combustion analysis within the altitude-corrected target range. Ambient CO at zero or trace. The heat exchanger passes inspection. We document this in writing. If a competitor has condemned the furnace, the documentation is available to dispute the quote.
  • Overfire discoloration without structural failure: Blue-to-purple discoloration and surface scale indicating rich-burn combustion history, without visible cracks or perforations. The heat exchanger is structurally intact but has been stressed beyond design intent. Recommendation: correct the altitude derate (manifold pressure adjustment), clean the burner ports if carbon deposits are present, and schedule annual borescope inspection. The heat exchanger may have 3–7 years of remaining service life if the root cause of the rich-burn is corrected.
  • Confirmed crack or perforation: Visible breach in the heat exchanger cell wall under borescope, with or without ambient CO present in the return air. A confirmed breach is a legitimate safety concern. The options and the appropriate urgency depend on the findings below.

Repair Options for a Confirmed Cracked Heat Exchanger

Option 1 — Heat Exchanger Replacement

Replacement of the primary heat exchanger assembly is possible on some furnace models where the manufacturer or aftermarket suppliers offer heat exchanger replacement parts. This option is most viable for furnaces in the 8–15-year age range where the rest of the system is sound (blower motor, control board, gas valve, and inducer are all functional), the failure is an isolated manufacturing or fatigue crack rather than distributed corrosion, and the furnace efficiency tier (90%+ AFUE) does not make a full system upgrade compelling on cost-effectiveness grounds. Heat exchanger replacement runs $600–$1,400 depending on the furnace model and part availability, plus labor ($300–$500 for a typical residential primary exchanger replacement).

Heat exchanger replacement is not viable on furnaces where:

  • Parts are not available (common on furnaces over 18–20 years old from discontinued product lines)
  • The failure is distributed corrosion across multiple cells (replacing one cracked cell leaves the corrosion mechanism active in adjacent cells)
  • The furnace is over 16 years old with other components at or near end of service life (a new heat exchanger in an aging blower motor, aging control board, and aging gas valve is not a 15-year repair)

Option 2 — Continued Operation with CO Detection

For homeowners who cannot arrange immediate replacement or heat exchanger replacement repair, continued operation of a confirmed cracked heat exchanger with CO detection in place is a risk-managed interim option. The conditions under which this is defensible:

  • CO detector(s) installed in sleeping areas and on each floor of the home, functioning and within their rated service life (most CO detectors require replacement at 5–7 years)
  • CO levels in the return air at the time of diagnosis are low (under 10 ppm at the return grille, trace in living areas — a crack that is producing 50+ ppm in the return air is a different risk profile)
  • The home has adequate ventilation (not sealed by both weather-stripping and interior doors in a way that can concentrate CO in sleeping areas)
  • The homeowner understands the risk and has a concrete plan and timeline for furnace replacement or heat exchanger repair

We document our findings and our discussion of this option in the service report. We do not recommend indefinite continued operation of a confirmed cracked heat exchanger without CO monitoring in place.

Option 3 — Furnace Replacement

The appropriate choice when the heat exchanger is confirmed cracked, the furnace is over 15 years old, other components are showing age-related degradation, heat exchanger replacement parts are unavailable or not cost-effective, or the homeowner wants to eliminate the safety concern definitively rather than manage it. We provide furnace replacement quotes during the same diagnostic visit when a confirmed cracked heat exchanger warrants it, including the full itemized estimate, AFUE upgrade comparison with utility payback calculation, and applicable rebate documentation for Dominion Energy Thermwise and IRA 25C.

Frequently Asked Questions

How do I know if a heat exchanger condemnation quote is legitimate?
Ask the contractor for documented evidence: a written service report that specifies the cell or cells where the crack was identified, the diagnostic method used (borescope inspection, not flame deflection test), the CO readings at the return air grille during operation, and photos or video of the finding under borescope. A legitimate condemnation should include all of these. A quote that says “cracked heat exchanger, recommend replacement” without specifying the location, the diagnostic method, or the CO measurement is not documented evidence — it is a recommendation without a foundation. Call us for a second opinion; our $89 diagnostic fee is the cost of verifiable documentation.
Can a cracked heat exchanger be repaired with a patch or sealant?
No — not legitimately. The high-temperature combustion environment inside a gas furnace heat exchanger (600–1,200°F at the surface) degrades any sealant or patch compound that is not the original heat exchanger metal. High-temperature epoxy patches, furnace cement applications, and similar field repairs on cracked heat exchangers may temporarily seal the breach but will fail within one to three heating seasons as the thermal cycling continues to stress the already-cracked metal around the patch site. We do not perform sealant or patch repairs on confirmed cracked heat exchangers, and we advise customers who have received this recommendation from other contractors that it is a temporary measure that delays the safety concern rather than resolving it.
My furnace is 8 years old and the heat exchanger has a crack — is replacement really necessary?
Not necessarily immediate replacement, but prompt action is appropriate. An 8-year-old furnace with a confirmed single-cell crack and a sound rest of the system is a candidate for heat exchanger replacement (if parts are available for the model) rather than full furnace replacement. An 8-year-old furnace is also likely still under its manufacturer’s limited heat exchanger warranty — most major manufacturers offer 20-year limited heat exchanger warranties on registered equipment. We verify warranty status during the diagnostic visit and file warranty claims on behalf of customers whose coverage criteria are met. If the warranty covers the replacement part, the out-of-pocket cost is labor only ($300–$500) rather than the full part-plus-labor cost.
How much does heat exchanger replacement cost versus furnace replacement?
Heat exchanger replacement runs $900–$1,900 total installed (part plus labor), depending on the furnace model and part availability. Full furnace replacement runs $4,800–$11,500 installed depending on efficiency tier and installation complexity. For a furnace under 12 years old with an isolated crack and parts available, heat exchanger replacement is usually the right economic choice. For a furnace over 15 years old, the cost difference between heat exchanger replacement and a full system upgrade narrows considerably when the remaining service life of other components is factored in, and the efficiency upgrade from an aging 80% AFUE furnace to a new 96% AFUE modulating unit may produce a payback in utility savings that makes the full replacement more attractive than the repair even on a pure economics basis.
What should I do right now if I have a cracked heat exchanger?
Three immediate steps: (1) Confirm you have working CO detectors on each level of the home and in all sleeping areas. If you do not, or if your detectors are over 5 years old, replace them today — they are available at any hardware store. (2) Call us or another licensed HVAC contractor for a documented second opinion if you received a condemnation quote without borescope photos and CO measurements. “We need to see it first” is the correct starting position before a $5,000–$11,000 decision. (3) If the crack has been confirmed by a contractor you trust, and CO is measurably present in your living space, shut the furnace off and use electric space heaters while arranging repairs — do not operate a furnace with a confirmed crack producing CO in the return air circuit without CO monitoring in the sleeping areas.

Contact Draper Heating & Air Conditioning

If you have received a heat exchanger condemnation quote and want documented evidence before making a $5,000–$11,000 decision, our $89 diagnostic includes borescope inspection, combustion analysis with CO measurement at the return grille, and a written report with photos. We serve Draper, Sandy, Bluffdale, Riverton, South Jordan, and Herriman with 24/7 emergency availability.

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