Burns & soot in a heat exchanger (C) Daniel Friedman Furnace Heat Exchanger Life Expectancy & Warranty Periods
Guide to cause & prevention of furnace heat exchanger failures

  • FURNACE HEAT EXCHANGER LIFE - CONTENTS: what is the life expectancy of a residential heating furnace or its heat exchanger? How long do furnaces last?Typical Residential Warm Air Heating Furnace Heat Exchanger Life. 13 Factors that Impact Residential Warm Air Heating Furnace Heat Exchanger Life. Should a Leaky Heat Exchanger be Repaired or Replaced? Table of Residential Heating Furnace Heat Exchanger Warranty Period
  • POST a QUESTION or READ FAQs about furnace heat exchanger life expectancy & warranty periods

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Furnace heat exchanger life:

In this article we discuss residential forced warm air furnace heat exchanger life in more detail, explaining the factors that impact the life of the heat exchanger, things you should do to maximize the life of the furnace heat exchanger, and similarly, things you should not do because they are likely to destroy your furnace before its time.

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Furnace Heat Exchanger Life & Warranty Periods

Typical Residential Warm Air Heating Furnace Heat Exchanger Life

Rheem Upflow / Horizonal Flow Furnace Heat Exchanger (C) InspecAPedia & Rheem ECCOWhat is a Heat Exchanger?

Furnace heat exchangers transfer heat from the burning fuel (typically LP gas, natural gas, or heating oil) into building air. In most designs combustion gases pass from the combustion source (oil or gas flame and combustion chamber) through the heat exchanger's interior tubing to an exhaust point that vents gases through the heater's flue and chimney (sketch at left).

What happens if a heat exchanger leaks?

If a heat exchanger develops a leak (through rust perforation or by cracking due to metal fatigue) the heating system is most likely unsafe and needs repair or replacement. There are two principal reasons to talk about furnace heat exchanger life:

1. Safety: a leaky heat exchanger can be dangerous, risking carbon monoxide poisoning.

2. Cost: although it is possible to replace a leaky heat exchanger on many furnace models (not all), the labor cost and total cost investment in such a replacement in an older furnace is questionable enough that more often the ultimate cost is that of a new heating system.

A while back at HEAT EXCHANGER LEAK TEST reader Marlin asked "what is the normal life of natural gas furnace?" to which we replied "Just about the warranty period - manufacturers know their equipment well; warranty periods run from 10 years to lifetime." But this was a bit too glib. Here we provide the details about the causes of leaks in furnace heat exchangers and about furnace heat exchanger life expectancy.

Why do we care about leaky furnace heat exchangers? Furnace heat exchanger leaks may vary from trivial - even below the limits of detection, potentially fatal.

Watch out: Dangerous carbon monoxide gas leaks (CARBON MONOXIDE - CO), potentially fatal, can be present intermittently depending on variations in heating system operation and building conditions. Actual risk of CO poisoning varies even when there is a leak in a furnace heat exchanger depending on where the leak is, its size, the fuel used (gas vs. oil) and other factors that we discuss in taxing detail in a companion article: HEAT EXCHANGER LEAK TEST.

13 Factors that Impact Residential Warm Air Heating Furnace Heat Exchanger Life

Photograph of furnace rust damage.

The top two most commonly-cited causes of leaks or failures of a forced warm air furnace heat exchanger are corrosion and metal fatigue.[21] To understand the actual causes of heat exchanger failures in a bit more detail is to know how to reduce the risk of this potentially dangerous and costly defect.

  1. Adjustment of the furnace burner (oil or gas), fuel to air mixture, or combustion air defects: any improper operation that causes the furnace burner to run too hot or too cool can damage the equipment in a variety of ways: thermal fatigue, condensation, production of corrosive agents.
  2. Airflow restrictions: anything that slows the flow of building air over the furnace's heat exchanger risks subjecting that component to high temperatures, increasing metal fatigue and shortening the unit's life.

    Examples of airflow problems include dirty air filters, crushed, damaged air ducts, even improper original duct system layout and design. Beware of more subtle dirt that slows air flow such as a dirty squirrel cage blower fan - a component not normally included in furnace cleaning jobs. .

    Greenheck points out that "Other than a corrosive environment, the airstream temperature rise is the largest factor driving heat exchanger material selection."[21]
  3. Equipment specifications, construction quality and materials of the furnace such as grade and thickness of steel used
  4. Fan limit switch operation or any event that subjects the heat exchanger to abnormally high temperatures. For example, . if the fan limit switch is modified, damaged, or improperly adjusted then the heat exchanger can be subjected to a too-high operating temperature or it may be subjected to abnormally high temperatures if the blower fan shuts off too early at the end of a heating cycle.
  5. Furnace type: while a multi-stage furnace is probably more economical to operate, this design may subject the heat exchanger to higher temperature fluctuations. (This concern may be offset by improved manufacturer's warranty terms.)
  6. Gas pressure: in gas-fired furnaces, if gas pressure is too low the furnace heat exchanger may be subjected to excessive wet-time increasing corrosion in the unit. In oil fired furnaces improper burner adjustment may produce similar corrosive effects if soot combines with moisture.
  7. Heat exchanger materials: some warm air heaters such as some models of Rheem's gas furnaces using a stainless steel construction assert improved corrosion resistance and resistance to thermal fatigue [12] . Heat exchanger materials need to resist both corrosion and the effects of temperature cycling. Commercial and indirect-fired heat exchangers in some commercial equipment offer alternatives to steel: aluminized steel (the aluminum corrodes to form an aluminum oxide resisting further corrosion), and stainless steel (chromium content resists corrosion by a mechanism similar to the aluminized steel product).[21]

    As aluminized steel approaches 1100°F the aluminum begins scaling, exposing the steel. This temperature corresponds to an airstream temperature rise of approximately 70°F. However, at temperatures below the aluminized steel scaling point, the aluminized steel tends to outperform stainless steel with respect to heat stress cracking.

    From this information, Greenheck recommends aluminized steel for temperature rises of 60ºF or less and stainless for temperature rises greater than 60ºF. For heating and ventilating applications and make-up air applications in mild climates where the airstream temperature rise is less than 60°F, aluminized steel will offer long furnace life and minimize the chance of heat exchanger stress cracking.

    For make-up air applications in cold climates where airstream temperature rise exceeds 60°F, stainless steel is recommended. [21]
  8. Installation: installation errors, even mechanical damage
  9. Maintenance level & frequency of the heating system; regular cleaning & maintenance extends equipment life. Oil burner soot forms corrosives when left in place in the off-use season. Failure to keep the heat exchanger clean subjects it to higher temperatures, potentially damaging this key component.

    If the furnace is capped by a cooling coil, maintenance must assure that its condensate is properly handled and the coil kept clean.
  10. Moisture: exposure of the heat exchanger to moisture and thus rust: leaky humidifier, especially a humidifier or A/C drip pan located above the heat exchanger; humidifier or condensate leaks onto the heat exchanger, chimney leaks from condensate or actual water entry; a heat exchanger in a furnace located in a wet or damp basement or crawl space is at extra risk of rust damage & perforation.

    The heat exchanger is also exposed to extra moisture simply from condensation if the system has long off-cycles during the heating season.

    Corrosion occurs in the heat exchanger with the combination of water primarily with nitrogen and sulphur [21] to create sulfuric acid and other corrosives.
  11. Operating duty cycle of the furnace
  12. Operating air speed: slower airflow around the heat exchanger may subject it to higher temperatures.
  13. Operating environment besides moisture listed above: e.g. a heater at an indoor pool exposed to chlorine means shorter life)

With all of these, and given that the manufacturers have a greater database of experience than the rest of us (and keep actual performance a trade secret), I figure we should quote anticipated furnace heat exchanger life as about that of its warranty period, excluding exceptional events. I will research for any updates to our list of scholarly articles on the topic and will include them in our article.

Photograph of rust on a furnace warning of unsafe heat exchanger.

Moisture dripping onto the heat exchanger

is evident when we see an add-on air conditioner evaporator coil atop an older furnace, questionable or leaky condensate handling, rust stains atop the furnace, and similar clues.

Inspecting inside the furnace below the A-coil or evaporator or cooling coil one might see actual rust damage to the heat exchanger. Even if damage is not immediately visible, don't assume that a visual inspection of the heat exchanger is comprehensive. It's not.

At below left we illustrate a hole burned/rusted through the heat exchanger of an old oil-fired furnace.

At below right we were concerned about the burned fragments in the left side of the photo.

Rust hole in furnace heat exchanger (C) DanieL Friedman Burns & soot in a heat exchanger (C) Daniel Friedman

Our photo at below left shows variation in the gas flame of that furnace - a possible indicator of a heat exchanger leak. At below right we see what I call "exfoliating rust" (red arrow) that shows up in thick flakes or chunks - this is not superficial rust.

Our blue arrow points to a pile of this rust debris beneath the gas burner in a furnace that was installed in a damp area - the heat exchanger is suspect even before a thorough inspection.

Rust hole in furnace heat exchanger (C) DanieL Friedman Burns & soot in a heat exchanger (C) Daniel Friedman

Our two photos below show a severely rusted gas furnace interior, and our red arrow (below right) points to a severe crack in the heat exchanger.

Rust hole in furnace heat exchanger (C) DanieL Friedman Burns & soot in a heat exchanger (C) Daniel Friedman

Should a Leaky Heat Exchanger be Repaired or Replaced?

LARGER VIEW of heating furnace parts and air flow, showing the heat exchanger

Just ask the equipment manufacturer. OK so everyone wants to sell you a new furnace or an expensive heat exchanger replacement. It's not just greed. No one wants to bear the risk of promising you that a repaired heat exchanger is safe.

Our photo at left shows the heat exchanger in a new gas furnace we installed in a Poughkeepsie NY Home.

We heard from folks describing repair attempts using high-temperature resistant epoxy, welding, and other low-cost solutions.

Any such repair is likely to void the manufacturer's warranty and each of them has a warning or three to keep in mind: epoxy may not bond reliably or may not withstand the furnace operating conditions;

MIG welding can avoid burning a big hole in the exchanger but if the welder is not an absolute expert the welding job may cause further metal fatigue and more heat exchanger cracking even larger than before; carbon monoxide gas is itself odorless and colorless; you may be depending entirely on carbon monoxide detectors for the life and safety of building occupants.

In fact Keith Prach, an expert on heat exchanger failures & testing notes that when a heat exchanger fails by cracking,

Cracks generally form at sharp corners and on or around welded seams. The stresses and forces at these locations make the metal more susceptible to crack initiation.[Prach later adds] Any area where the metal of the heat exchanger is configured with curves, ribs (concave or convex), indentations, dimples, or hot spots..., and weld seams are most likely to crack. [1]

Rusted leak-suspect heat exchanger on a home heating furnace (C) Daniel FriedmanPrach continues to describe the initial state of heat exchanger cracks as small, difficult to see, but growing ever larger as the heater goes through heating cycles. Adding welds, in my OPINION means adding stress points for future heat exchanger cracks.

OPINION: I would not try to repair a furnace heat exchanger.

If the furnace is generally in good condition and operates at a good efficiency but has suffered a cracked heat exchanger, one might consider a heat exchanger replacement when the cost of the total job is about half the cost of a new furnace and of course also if the furnace heat exchanger remains covered by the manufacturer's warranty.

On older furnaces and non-factory warranty heat exchanger replacements we're left with some questions: is the new heat exchanger warranted? Is the work proper, complete, safe? Were the same furnace heat exchanger leak tests performed after the repair as before?

List of Furnace Heat Exchanger Warranty Periods & Life Expectancies

Table of Residential Heating Furnace Heat Exchanger Warranty Periods

Manufacturer Product Warranty or Expected Life for Furnace Heat Exchanger
Composite opinion from various sources Typical heat exchanger life - steel 15-20 years [19]
Composite opinion, several sources Typical heat exchanger life - cast iron 40-50 years
Air-Ease Furnace Warranty   [data needed]
American Standard Furnace Warranty Platinum ZV / SV / Gold ZM furnace (example)

Limited lifetime

Bryant Furnace Warranty Gas, Model 987M Lifetime
Bryant.com 4/11/13
Carrier Furnace Warranty Oil furnace Lifetime
if properly registered in 90 days, else 20 years.
Gas, non-condensing 20 years
Gas, condensing, tub & fin 2dary Heat Exch Life or 20 years (model dependent); subsequent owner: 20 years.
Small packaged products, aluminized steel heat exchanger 20 or 15 years as above
Small packaged products, stainless steel heat exchanger Life or 20 years as above
Fedders Furnace Warranty
Airwell-Fedders Warranty
Packaged units, residential 5-year limited ?
Texas Furnace Note: Airwell-Fedders may not honor Feddres HVAC warranties
Goodman Furnace Warranty Gas Furnace GMVC95 Lifetime limited warranty
Greenheck Furnace Warranty Indirect gas-fired furnaces, Commercial Units Lifetime limited warranty
Heil Furnace Warranty

Residential Gas Furnaces

Lifetime or 20 years
Warranty transferred to subsequent owner = 20 years, all products

heil-hvac.com 4/11/13

F8MX(N/L), G8MX(N/L)
20 years
heil-hvac.com 4/11/13
Janitrol Furnace Warranty
(sold through Sears Roebuck)
  [data needed]
Luxaire Furnace Warranty All systems Limited lifetime warranty
luxaire.com 4/11/13
Magic-Chef Furnace Warranty    
Maytag Furnace Warranty Gas furnace M1200-series 5 years (if not registered)
12 years, extended to lifetime
maytaghvac.com 4/11/13
Premier Furnace Warranty   [data needed]
Rheem Furnace Warranty Gas furnace heat exchanger 20 years
Gas furnace, high efficiency economy 20 years on Primary & Secondary heat exchangers
Gas furnace, high efficiency & high efficiency 2-stage units Limited lifetime
Sears Homart Furnace Warranty   [data needed]
Singer Furnace Warranty
Singer American Furnace Warranty
  [data needed]
Tappan Furnace Warranty All furnaces Limited lifetime
tappan.net 4/11/13
Trane Furnace Warranty Gas furnaces Limited lifetime
trane.com 4/11/2013
Oil Furnaces Limited lifetime
trane.com 4/11/2013
Whirlpool Furnace Warranty Gas Furnaces Limited lifetime
whirlpoolcomfort.com 4/11/13
Gas Furnaces, stainless steel heat exchanger
E.g. WGFM29/WGFD29
Limited lifetime furnace replacement
whirlpoolcomfort.com 4/11/13
York Furnace Warranty Affinity or LX series furnaces Limited lifetime
york.com 4/11/2013
Affinity or LX packaged units 20-year warranty
Latitude 20-year warranty
Latitude Model TG95 Lifetime


Watch out: most furnace heat exchanger warranties as well as overall product warranty require that you register your heating system within a limited time period after its installation, typically within 60 or 90 days. If you fail to register a more limited warranty of shorter duration may apply.

Watch out: OPINION: product warranties including furnace heat exchanger warranties are sometimes more of a marketing tool than a reliable promise. The simple comparison of warranty terms such as number of years of warranty coverage does not reflect the ease or difficulty you may have actually making a successful warranty claim among various companies.

For a comparison of the environmental impact and life variations of different types of heating & cooling equipment seen Shah (2008) [17] in our references.

CONTACT US to submit additional furnace heat exchanger warranty data

We recommend that you never rely on visual inspection alone to determine the safety of a furnace heat exchanger. Readers of this document should also

Furnace Heat Exchanger Leak Inspection & Testing

We include the text from historical articles on methods used for testing furnace heat exchangers for leaks, and the allowable or standards for heat exchanger cracks, holes, leaks, or carbon monoxide hazards from such leaks.



Continue reading at HEAT EXCHANGER LEAK TEST or select a topic from the More Reading links shown below.

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Frequently Asked Questions (FAQs) about about furnace heat exchanger life expectancy & warranty periods


Could you tell me what the normal life expectancy of a home furnace heat exchanger is? Many thanks. - J.F. 3/11/2013


Thanks for the question - it prompted us to expand our original furnace warranty information in the article above.


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