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Al’s Plumbing, Heating & A/C in Plano, Texas provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (same company as American Standard) and Coleman HVAC (same company as York HVAC).

Al’s also provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s is near your home in Plano, Allen, and Frisco.  We service all homes in southern Collin and Denton Counties with no travel charges.

Call Al’s today to discuss any concerns or problems you have with your HVAC System or Plumbing.  We will arrange an appointment at your convenience and offer 24/7 Emergency Service.

This article is about ways to determine if a gas furnace has a cracked heat-exchanger.   Al’s Heating & A/C provides repairs of all brands of Central A/C, Gas or Electric Furnaces, & Heat Pumps.  Al’s sells and installs new HVAC systems from American Standard (made by the same company as Trane), Ameristar (made by same company as American Standard), and Coleman HVAC (made by the same company as York HVAC).    Al’s also provides repairs and replacements of every plumbing component throughout your home.

Calls Al’s today to discuss any concerns or problems you are having.  We can arrange an appointment at your convenience.

photo of heat exchanger in gas furnace

Photo Source: Dreamstime

SHOWN: A New Gas Furnace Heat Exchanger 

Click Here To See A Cracked Gas Furnace Heat Exchanger:  Photo Of Cracked Heat Exchanger

How To Determine If A Furnace Has A Cracked Heat Exchanger 

Most problems with a gas furnace can be repaired, though the repair cost is not always justified.  Most repairs require a component that will return the furnace to normal and safe operation.  A furnace with a cracked Heat-Exchanger is usually an exception, because of the cost of the repair.

Note: Electric furnaces do not have a heat-exchanger.

The problem with finding a crack in a furnace heat exchanger is that you can see very little of the heat exchanger without disassembling the furnace.

There are a two ways that are typically accurate indicators a heat exchanger is cracked.  You must do both to ensure an answer you can be confident with.

1. If The Heat Exchanger Is Cracked, Air Is Forced Into The Combustion-Chamber (where the burners are located) When The Blower Fan Turns On.  This Distorts The Burners’ Flames. 

Click Here To See Flames Distortion While Blower Is Running:

 Cracked Heat Exchanger Causes Distorted Flames

In many cases, owners discover they have a cracked heat-exchanger because the furnace shut down.  Furnaces are equipped with a safety-feature called a “Flame Rollout Limit Switch”.  If the flame comes outside the proper area, the Flame Rollout Limit Switch senses this and shuts the furnace down to protect itself and your home.

Click Here To See A Flame Rollout Limit Switch: Photo Of Flame Limit Rollout Switch

 

2. If A Heat-Exchanger Is Cracked, Air Forced Into The Combustion-Chamber Will Cause The Oxygen Reading In The Furnace’s Exhaust To Rise To Abnormal Levels.   This Will Be Detected With A Combustion Gasses Tester.

If you have been told your furnace’s heat exchanger is cracked, ask the tech to show you the exhaust’s Oxygen Readings when:

  • The Burners Are On & Blower Is NOT Running.  This occurs while the furnace is warming up before the blower turns on.
  • If the Oxygen Reading rises as the furnace warms up, this is because the crack in the heat-exchanger is opening larger as it heats up.
  • As the crack gets larger, increasing amounts of oxygen enter the combustion chamber while the furnace is warming up.

Click Here To See Oxygen Reading Climb (at time 1:09) As Furnace Is Warming Up:

CRACKED Heat Exchanger – Oxygen Reading Rises While Furnace Is Heating Up (at time 1:09)

 

  • Burners Are On and Blower IS Running.
  • If the Oxygen Reading rises to abnormal levels once the lower turns on, this is because the blower is pushing air into the combustion-chamber through the crack in the heat exchanger.

 

Click Here To See Normal Oxygen Reading After Blower Turns On (at time 2:40):

Oxygen Reading Remains Stable: Heat-Exchanger NOT Cracked (at time 2:40)

 

If the heat exchanger is cracked, the Oxygen Reading will change a lot when the blower turns on.  This is because air is leaking (through the crack in the heat exchanger) into the combustion chamber.  The extra air will cause the Oxygen reading to change notably.  In the video above the furnace techs says the Oxygen Reading could rise as high as 40-50% if the heat-exchanger is cracked.

NOTE:  This test should be performed by a trained HVAC Technician.

Heat-Exchanger Cracks

Click Here To See A Cracked gas Furnace Heat Exchanger:  Photo Of Cracked Heat Exchanger

Heated metal expands.  As metal cools, it contracts. This recurring expansion & contraction is part of the normal furnace heating cycle. All heat-exchangers eventually fail due to metal fatigue caused by expansion and contraction.  Metal fatigue can be witnessed by bending a paperclip back and forth.  Over time, the metal fatigues and the paper clip breaks.

Some factors that can accelerate heat-exchanger failure.  These factors are usually:

  • Poor furnace maintenance
  • Improper installation
  • Furnace manufacturer design

In the past, the only way to check for heat-exchanger crack(s) was to perform a visual inspection.  Today there are scopes & camera equipment to help search for cracks.  But even with these devices, it’s still not possible to see the entire heat-exchanger.   Unless the furnace is disassembled to the point so you see the entire heat-exchanger, a visual inspection can miss a crack(s).   In the photos just above, you can see how enclosed the heat-exchanger is inside the furnace.

If You Are Told Your Furnace Has A Cracked Heat-Exchanger

  • Ask the technician to show you the crack.
  • If the tech cannot show you the crack.  Stop there and get a second opinion.
  • Ask the tech to show you the results from a Combustion-Gases Analysis.
  • If this test was not performed, and the tech is not equipped to perform one.  Stop there and get a second opinion.

Immediately Get A Second Opinion

  • Find a different HVAC Contractor who performs Combustion-Gases Testing / Analysis (it’s called different names).  This step is often part of a furnace tune-up.  Get tune ups only from HVAC contractors who include exhaust-gases testing.
  • Don’t tell them why you want the test. Simply order a furnace tune-up.  Ask to confirm their furnace tune-up includes combustion-gases testing.
  • Short of seeing a visible crack, a combustion-gases analysis is the surest way to determine if the heat-exchanger is cracked.

 

A Cracked Heat-Exchanger:

Either The Heat-Exchanger Or Furnace Must Be Replaced

Your Options If The Heat-Exchanger Has Cracked

  • Replace The Heat Exchanger.  If the heat exchanger is under warranty, this is a good way to go.  If the part is under warranty but not available, ask the contractor to call the manufacturer and request the cost of the heat exchanger be removed from the new furnace’s price.  The warranty will pay for the part, you must pay installation labor charges.
  • If the heat exchanger is not under warranty, compare the cost to replace it (parts & labor) compared to a replacement furnace.   Also consider the factors just below.
  • Replace The FurnaceFactor in the existing furnace’s efficiency & age.  There are several other expensive furnace components that can fail with time.  Two are the control-board (the furnace’s brain) and the blower fan.  If a furnace is out of warranty and more than 10 years old, it’s likely best to replace it.

The Benefits Of A Combustion-Gases Analysis

  • With a cracked heat-exchanger, the amount of oxygen inside the combustion-chamber rises while the blower fan is running.  This is because air is entering the combustion-chamber through the crack in the heat-exchanger.  This raises the amount of oxygen in the exhaust gases.
  • It tests under actual operating conditions.
  • It can be easily done during a normal service call that includes combustion gases testing.
  • It may also indicate how dangerous a crack is.

Example: With a severe crack, the (combustion-gases) oxygen level rises considerably while the blower fan is running.  This gives the tech more confidence the heat-exchanger is cracked.   Test readings provide documentation that a furnace with a cracked heat-exchanger is not safe.  It may be “Red Tagged” meaning it’s immediately shut down and taken out of service.

SOURCE: https://www.achrnews.com/articles/103307-checking-for-cracked-heat-exchangers    Established in 1926, The Air Conditioning, Heating and Refrigeration weekly news magazine is the HVAC Industry’s direct communications link for HVAC Contractors and those buying their services.

WHY A FURNACE IS RED TAGGED

Red-Tagging  is when a Furnace Technician or Utility Representative shuts a furnace down because it is unsafe.    The best way to avoid a furnace being red tagged is to keep the heating system well-maintained.

If Your Furnace Is Red Tagged: 

  • Ask the technician to show you specifically what caused the furnace to be red tagged.
  • Get a second opinion right away.
  • Tell the contractor you have a red-tagged furnace.   Many contractors will make every effort to provide for Emergency or Next Day Service when a furnace is disabled.

Why To Get A Fall Furnace Tune Up

Get A Furnace Tune-Up Each Fall.  This can save you the worry, and higher Emergency Service rates because your furnace shut stopped working during cold temperatures because of  something that would likely have been discovered during a Tune-Up.

Example 1:  A dirty Flame-Sensor will stop a furnace from working.  It’s most likely to happen when it’s very cold and the furnace is running a lot.  As part of a Furnace Tune-Up, the Flame-Sensor will be cleaned.

The Flame Sensor is a located at the burner assembly.  It sits in front of the burner’s flame.  The purpose of the flame sensor is to confirm a flame is present whenever the gas valve is open.  If the flame sensor is dirty, and cannot determine a flame is present, the furnace will close the gas valve and shut down to protect the home from a gas explosion.

Example 2: Air entering & exiting the burners has dust particles in it. These dust particles begin to form a coating of dust on and around the burners.  This needs to be cleaned away for proper and efficient burner operation

HOW The Heat-Exchanger Keeps Combustion-Gases Separate

From The Home’s Indoor Air  

  • Burners create heat + combustion-gases.

  • Heat + combustion-gases move inside the heat-exchanger’s chambers / pipes.

  • The heat is extracted as it warms the heat-exchanger’s chambers / pipes.

  • Exhaust-gases then exit the furnace.

  • Blower fan turns on and blows the home’s indoor air along the outside of the heat exchanger’s chambers.

  • Heated air is then recirculated throughout the home.

This YouTube Video Shows How a Heat-Exchanger Works: How A Furnace Heat Exchanger Works

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Al’s Plumbing, Heating & A/C in Plano, Texas provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (same company as American Standard) and Coleman HVAC (same company as York HVAC).

Al’s also provides full service plumbing maintenance, repairs and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s is near your home in northeastern Dallas, Plano & Garland.  We service all homes in southern Collin and Denton Counties with no travel charges.

Call Al’s today to discuss any concerns or problems you have with your HVAC System or Plumbing.  We will arrange an appointment at your convenience and offer 24/7 Emergency Service.