Heat Exchanger Repair in Kirkwood and West St. Louis County
The heat exchanger is the component that physically separates the combustion gases inside the furnace from the supply air that circulates through your home. Combustion products — including carbon monoxide, nitrogen oxides, and water vapor — pass through the heat exchanger’s interior tubing on their way to the flue. The supply air passes over the exterior of the heat exchanger, picking up heat through the metal wall that separates the two streams. When that metal wall cracks, combustion products including carbon monoxide enter the supply air and circulate throughout the home. Carbon monoxide is colorless, odorless, and produces flu-like symptoms (headache, fatigue, confusion, nausea) at low exposure levels and unconsciousness or death at higher levels. Heat exchanger inspection is the most important safety inspection performed on residential furnace equipment, and Hawkeye inspection borescope verification on every diagnostic visit and tune-up is how we catch cracks before they produce a CO event.
Why Heat Exchangers Crack
Heat exchangers crack through accumulated stress over the equipment’s service life. Specific failure modes:
- Thermal cycling stress. Every heating cycle expands the heat exchanger metal as combustion gases heat it, then contracts the metal as the equipment cycles off. Over 15–30 years of typical residential operation (10,000–50,000 cycles depending on equipment runtime), metal fatigue accumulates at stress concentration points — typically at weld seams, bend radii, and section transitions.
- Restricted airflow. Equipment running with restricted airflow (dirty filter, undersized ductwork, blower motor wear, dirty evaporator coil for AC-equipped systems) produces elevated heat exchanger temperatures, accelerating thermal fatigue. This is the most preventable cause of premature heat exchanger failure. Annual tune-up static pressure measurement and filter replacement catches airflow restriction before it damages the heat exchanger.
- Condensation on non-condensing equipment. 80% AFUE equipment is designed to operate above the flue gas dew point — the combustion products should leave the heat exchanger hot enough to prevent water vapor condensation. Equipment with restricted airflow or oversized capacity may produce condensation inside the heat exchanger, accelerating corrosion of the metal.
- Improper condensate handling on condensing equipment. 92%+ AFUE condensing equipment produces acidic condensate (pH 3–5 typical) that must drain properly through the secondary heat exchanger and out the condensate line. Clogged drains, improper slope, or freeze damage can cause condensate to back up into the heat exchanger, accelerating corrosion.
- Manufacturing defects. Specific equipment generations have had higher-than-typical heat exchanger failure rates due to manufacturing process issues. Affected manufacturers have addressed these through warranty service programs.
- Burner flame impingement. Improperly adjusted gas pressure, dirty burners, or improper combustion air can cause flame impingement on the heat exchanger surface, producing localized overheating and accelerated cracking.
Cracked Heat Exchanger Symptoms
Cracked heat exchangers don’t always produce obvious symptoms before becoming dangerous. Some symptoms that may indicate cracking:
- Flu-like symptoms (headache, fatigue, dizziness, nausea) that improve when leaving the home and return when re-entering, particularly during heating season
- CO alarm activation, even at low levels
- Soot accumulation around the furnace or in supply registers
- Yellow or orange burner flame (should be blue with stable flame pattern; yellow or unstable flame indicates improper combustion that often accompanies heat exchanger issues)
- Persistent “burnt” or metallic smell from supply registers during heating operation
- Visible signs of physical damage to the heat exchanger during inspection (rust, soot, cracks, perforations)
- Elevated CO measurements during combustion analysis
If carbon monoxide alarm has activated in your home, evacuate immediately, call 911, and contact your utility company to shut off gas service. Do not re-enter the home until first responders verify safe CO levels.
How We Inspect for Heat Exchanger Cracks
Step 1: Combustion Analysis
Bacharach Fyrite Insight Plus measurement at the flue. CO air-free measurement quantifies combustion product carbon monoxide independent of dilution from excess air. Healthy residential equipment produces under 100 ppm CO air-free at steady-state operation. Elevated readings (100–400 ppm) indicate combustion issues that may include heat exchanger cracks; readings above 400 ppm indicate serious safety concerns requiring immediate attention.
Step 2: Hawkeye Inspection Borescope
The Hawkeye inspection borescope is the primary diagnostic tool for heat exchanger inspection. The flexible camera probe enters the heat exchanger through access points (typically the burner compartment or flue connection) to allow direct visual inspection of interior surfaces. Inspection covers:
- Visible cracks at any size or location. Even hairline cracks in primary heat exchanger metal are replacement-warranting.
- Carbon scoring from improper flame impingement, indicating combustion adjustment issues that may have caused or accompanied heat exchanger damage.
- Condensate damage on condensing equipment, where acidic condensate corrosion has perforated or thinned the metal.
- Weld seam condition, particularly at the section transitions where stress concentrations typically occur.
- Bend radius condition, where the heat exchanger metal is most stressed during thermal cycling.
- Soot accumulation patterns that indicate combustion issues or potential leaks.
Photos and video documentation of borescope inspection go on the work order. For confirmed heat exchanger cracks, the equipment is shut down pending replacement — we don’t release the furnace back to operation with a known cracked heat exchanger.
Step 3: Visible External Inspection
Visual inspection of accessible heat exchanger surfaces from outside the unit (where geometry permits): inspection panel access, burner compartment access, blower compartment inspection looking for visible damage or unusual conditions.
Step 4: Smoke or Tracer Gas Test (When Indicated)
For ambiguous findings where borescope inspection is inconclusive, additional verification with smoke pencil at heat exchanger seams (with blower running, smoke draws toward any crack opening) or tracer gas detection (specific commercial products designed for HVAC heat exchanger inspection) can confirm or rule out cracking.
Repair Scope Decisions
Equipment Under Manufacturer Heat Exchanger Warranty
Most residential equipment carries a long heat exchanger warranty — typically 20 years on top-tier units, 10 years on mid-tier, lifetime on premium units like the Lennox SLP99V. For equipment under warranty, the manufacturer covers the replacement heat exchanger; the customer pays labor and any associated component costs.
Heat exchanger replacement is a significant labor operation:
- Equipment disassembly to access the heat exchanger
- Refrigerant recovery if the evaporator coil sits above the furnace (common configuration in upflow furnaces)
- Heat exchanger removal and replacement
- Reassembly with appropriate gaskets and sealants
- Refrigerant recharge and system verification
- Combustion analysis verification of safe operation
Typical labor cost for warranty heat exchanger replacement: $1,200–$2,400 depending on equipment access and configuration. Plus any associated component replacement (filter-drier, refrigerant, gaskets).
Equipment Outside Heat Exchanger Warranty
For older equipment (typically 11+ years on mid-tier units, 16+ on top-tier with longer warranty), the heat exchanger may be outside warranty coverage. In this case, customer pays both replacement parts and labor:
- Replacement heat exchanger parts: $400–$1,400 depending on equipment
- Labor: $1,200–$2,400 same as warranty replacement
- Refrigerant recovery and recharge: $300–$700
- Associated components: $100–$300
- Total typical cost: $2,000–$4,800 all-in
For equipment 13+ years old with an out-of-warranty heat exchanger failure, replacement frequently doesn’t make economic sense compared to complete furnace replacement. A new 92–96% AFUE furnace installed runs $4,800–$7,200, with new manufacturer parts warranty (typically 10 years parts, 20 years heat exchanger on the new equipment) and improved efficiency over 13-year-old equipment with 80–90% AFUE rating. We present both options with itemized costs and let the customer decide.
Why We Don’t Field-Repair Heat Exchanger Cracks
Some HVAC contractors offer “heat exchanger repair” via patching, welding, or sealant application. Purisync does not perform heat exchanger field repairs. The reasons:
- Manufacturer specifications. Carrier, Trane, Lennox, Bryant, Rheem, Goodman, and other manufacturers do not approve field repair of cracked heat exchangers. Field repair voids manufacturer warranty.
- Safety reliability. Field-patched heat exchangers are difficult to verify as fully sealed. A patch that holds during the test may fail during thermal cycling, producing the original CO leak with no warning indication.
- Code compliance. Most jurisdictions require certified replacement of cracked heat exchangers, not field repair. Some areas explicitly prohibit field repair under municipal mechanical code.
- Liability exposure. A field-repaired heat exchanger that fails and produces CO exposure creates substantial liability for the contractor who performed the repair.
If you’ve been quoted a heat exchanger “repair” by another contractor, we recommend getting a second opinion on the recommendation. Either the original diagnosis was incorrect (no actual crack), or the proposed repair is non-compliant with manufacturer specifications and code requirements.
Frequently Asked Questions
- How much does heat exchanger replacement cost in Kirkwood?
- For equipment under manufacturer heat exchanger warranty (typically 20 years on top-tier, 10 years on mid-tier, lifetime on premium units like Lennox SLP99V), the manufacturer covers the replacement part. Customer pays labor ($1,200–$2,400 depending on equipment access), refrigerant recovery and recharge if applicable ($300–$700), and associated components ($100–$300). For equipment outside warranty, replacement heat exchanger parts add $400–$1,400. Total cost typically $1,500–$3,400 for warranty replacement, $2,000–$4,800 for out-of-warranty replacement. Equipment 13+ years old with out-of-warranty heat exchanger failure frequently favors complete furnace replacement ($4,800–$7,200) over heat exchanger-only repair.
- How does Purisync confirm a cracked heat exchanger?
- Hawkeye inspection borescope provides direct visual inspection of the heat exchanger interior. The flexible camera probe enters through burner compartment or flue connection access points to inspect interior surfaces. Inspection covers visible cracks (any size, including hairline), carbon scoring from flame impingement, condensate damage on condensing equipment, weld seam condition, bend radius condition, and soot accumulation patterns. Photos and video documentation go on the work order. For ambiguous findings, smoke pencil testing or tracer gas detection provides additional verification. Bacharach Fyrite Insight Plus combustion analysis at the flue measures actual CO production during operation — elevated readings often accompany heat exchanger damage. Equipment with confirmed cracks is shut down pending replacement.
- What are the signs of a cracked heat exchanger?
- Symptoms aren’t always obvious before becoming dangerous, which is why annual borescope inspection is important. Possible indicators: flu-like symptoms (headache, fatigue, dizziness, nausea) that improve when leaving the home and return when re-entering during heating season, CO alarm activation even at low levels, soot accumulation around the furnace or in supply registers, yellow or orange burner flame (should be blue), persistent burnt or metallic smell from supply registers during heating, visible physical damage during inspection (rust, soot, cracks, perforations), and elevated CO measurements during combustion analysis. If your CO alarm has activated, evacuate immediately, call 911, and contact your utility to shut off gas service before re-entering.
- Does Purisync field-repair cracked heat exchangers?
- No. Purisync does not perform field repairs (patching, welding, sealant application) on cracked heat exchangers. Reasons: manufacturers (Carrier, Trane, Lennox, Bryant, Rheem, Goodman, etc.) do not approve field repair and consider it a warranty-voiding modification; field repairs are difficult to verify as fully sealed and can fail without warning indication during thermal cycling; most jurisdictions require certified replacement rather than field repair; liability exposure from a failed field repair producing CO exposure is substantial. If you’ve been quoted a heat exchanger repair by another contractor, get a second opinion. Either the original diagnosis was wrong (no actual crack), or the proposed repair is non-compliant with manufacturer specifications and code requirements.
- What causes heat exchangers to crack?
- Most common causes: thermal cycling stress over 15–30 years of equipment service life (the natural end-of-life mode for properly operating equipment); restricted airflow (dirty filter, undersized ductwork, dirty evaporator coil, blower motor wear) producing elevated heat exchanger temperatures; condensation on non-condensing equipment running below flue gas dew point; improper condensate handling on condensing equipment causing acidic corrosion; manufacturing defects in specific equipment generations (addressed through warranty programs); and burner flame impingement from improperly adjusted gas pressure or dirty burners. Annual tune-up combustion analysis and static pressure measurement catches developing issues before they cause heat exchanger damage. Properly maintained equipment typically reaches its service life expectation; equipment with neglected maintenance often fails 5–10 years earlier than design life.
Contact Purisync Heating and Air
For heat exchanger inspection, suspected CO production diagnosis, or replacement service, contact our 325 N Kirkwood Road office at (314) 338-5111. If your CO alarm has activated, evacuate immediately and call 911 before contacting us.
- Emergency Line (24/7): (314) 338-5111
- Address: 325 N Kirkwood Rd #245, Kirkwood, MO 63122
- Email: info@purisyncheatingairconditioning.xyz
- St. Louis County Mechanical Contractor License: #MC-2014-08439-STL
- Kirkwood Business Registration: #BL-2014-1187
- EPA Section 608 Universal: #608U-2014-385721
Office Hours
- Emergency Service: 24 hours a day, 7 days a week
- Office Staff: Monday – Saturday, 9:00 AM – 5:00 PM
- Closed: Sundays and State/Federal Holidays (emergency line always active)