The Problem

Heat Exchanger Cracks Rarely Cause Carbon Monoxide, But Require the Most Time to Identify

Because heating service people have been trained to inspect heat exchangers for minor cracks, they spend the majority of their service time in your home doing just that — looking for cracks. Unfortunately, they really haven’t been trained to survey the entire home and find out how it is operated and to determine whether there is adequate combustion air and whether fresh-air intakes are required.

Basically, they walk past the potentially fatal problems with combustion air and flues to look for heat exchanger cracks that rarely affect the indoor environment.

If you have a typical, residential 65% to 80% AFUE, forced-air gas furnace with an air-conditioning coil and duct work attached to it, then carbon monoxide from a heat exchanger crack is NOT going to occur. At least in 99% of the cases.

There’s always an outside chance that an odd-ball installation creates a problem. If you have an old gravity-furnace, or floor furnace or duct-furnace with a propeller fan, or a suspended unit heater, then it’s a different story. Even old Williamson and AFCO furnaces could dribble carbon monoxide into the home if there was no a/c coil on the furnace and the duct work was over sized.

However, furnaces equipped with air-conditioning coils and duct work attached don’t bleed carbon monoxide from the fire-side of the heat exchanger to the indoor-airstream (through a hole or crack.) The indoor blower creates too much air pressure inside the furnace cabinet. Any time there’s a hole or crack, air moves from the blower air stream, through the crack, INTO the heat exchanger. It’s never the other way around.

Somehow safety issues have turned a simple
problem into a rushed, selling situation
and a FORCED furnace replacement.

At the same time, the real safety problems,
the kind that causes death and injury,
are being ignored.

Somehow, it seems like the HVAC industry has ignored the fact that modern furnaces don’t operate the same way the original coal and gas-fired gravity furnaces did. When those early furnace had a breach in their heat exchangers, carbon monoxide, flue gas and soot were definite problems.

That changed when more compact furnaces were developed with integral blowers and air-conditioning. Unfortunately, the testing agencies and “authorities having jurisdiction” felt it would be safer to simply require ANY heat exchanger with a defect be replaced.

Almost every natural gas utility has mandated (made it part of their policy) that gas furnaces be replaced (or their heat exchangers replaced) if a hole or crack is detected, no mater how small. Consequently, service companies make furnace heat exchanger checks their high priority when performing routine maintenance or repairs.

Many local ordinances require you to have the gas utility “inspect” your gas furnace to insure it operates safely and the heat exchanger is intact before a change in property ownership can take place.

In fact, if you are trying to sell your home, this is one area where you can not negotiate with a potential buyer. You are REQUIRED to replace the furnace (or heat exchanger) before the sale can proceed.

This situation may appear to be OK from a safety standpoint, but consider the following:

  • The reason heat exchangers appear to be critical to safety is because of a misguided belief that a crack or hole in a heat exchanger will allow carbon monoxide to enter a home. For standard efficiency, 80% AFUE or less furnaces, this is a myth.
  • The fear of carbon monoxide from a simple heat exchanger crack is a hold over from the “old” days of “gravity furnaces” with pot-belly (round) heat exchangers. These furnaces might be coal-fired, oil-fired or gas fired. In many cases they were upgraded with gas conversion burners or in-shot burners (circa 1950’s.) Splits in those heat exchangers caused problems with carbon monoxide entering the home. The coal-fired and oil-fired burners produced plenty of other unsavory gasses besides carbon monoxide so it was usually easy for an occupant to tell that something “bad” was in the air. They could smell it or it would make their eyes water. With gas conversion burners, very little odor was emitted which made it hard for folks to know that their heat exchanger had split open.  In fact, gas conversion burners had the ability to “push” the products of combustion into a home’ s air stream and could sometimes produce high levels of carbon monoxide.
  • Gas furnaces with heat exchangers made in the last 20 to 30 years do NOT emit carbon monoxide just because of a crack or hole. If a furnace is generating high levels of CO, there are other problems that need to be identified and solved. When you see diagrams where they’ve circled a little hairline crack and are calling it dangerous … well let’s just say that’s what they may have been taught, but it is not the facts.
  • Visual heat exchanger checks are questionable at best. Short of dismantling the furnace, there is NO definitive way to guarantee that a heat exchanger does NOT have a crack or hole. In many heat exchangers, it’s almost impossible, even with a remote camera, to inspect all surfaces for cracks.

    One of the better detection methods currently being used is a lighted remote camera (camera on a stick) with a water sprayer. They spray water on one side of the heat exchanger and use the camera to see wet cracks on the other side. But even this method is not a 100% guarantee that the heat exchanger is intact. 

  • Here’s the important point: the conditions that lead to carbon monoxide poisoning are usually ignored because mechanics are focused on gas appliances, specifically heat exchangers, as the likely culprits. Consequently the home is never checked to insure it can safely support the gas appliances (combustion air and properly sized flue.) The home owner is never cautioned about using their attic fan or how the furnace flue and operating other devices (like a Jenn-Air or kitchen exhaust hood) can cause carbon monoxide problems. They also fail to highlight how the home’s construction can have a big impact on carbon monoxide safety. (This is the point of this web site and the report Carbon Monoxide Myths.) 

Fear of CO is the Easy Way to make a Sale

Here’s the fastest way to make a furnace sale – perform a heat exchanger check while doing routine maintenance or repairs. (Most service companies and gas utility providers mandate that heat exchanger checks be performed whenever a furnace is serviced.)

If there’s a “crack” in the heat exchanger, a sale of some sort is almost guaranteed. In effect, the $49.00 furnace “clean and check” becomes a potential $3,000 furnace installation. (The cheaper the “clean and check”, the more likely it is that your furnace will have a problem.) In fact, there are outfits that make a good profit teaching companies how to find heat exchanger cracks – and tout their classes as “replacement sales generators”.

With all the publicity about carbon monoxide and heat exchangers, the customer’s anxiety level will be high enough that they won’t be asking many questions. They will not be in a position to get competitive bids which makes the sale a fairly easy task.

To be fair, you should understand that local ordinances and the AGA “require” that furnaces with a heat exchanger crack or other safety problem be “red tagged” and shut down. Most natural gas providers also require a red tag when a cracked heat exchanger is discovered. Most HVAC schools teach students that a heat exchanger crack is a severe safety issue requiring that the equipment be taken out of service. In other words, heating contractors think they must red tag the furnace if it has a bad heat exchanger.

The gas utilities promote heat exchanger checks and are happy to see new, more efficient gas furnaces being installed.

Why Holes Are Profitable

Needless to say, the smallest hole in a heat exchanger becomes a sales opportunity once a service technician spots it. In many cases, they spend more time looking for the little hole or crack, than they do inspecting the rest of the furnace, electrical system and flue.

The bottom line is that you are at the mercy of the technician looking at your equipment. If you deal with reputable service companies that employ people who are honest, you’ll be OK.

Going for the “cheapest” rate when selecting a service company could prove to be a lot more expensive in the long run. Ask around, check with your friends and neighbors. Use Angie’s List and check with your local BBB (Better Business Bureau.)

Like it or not, service people in many organizations receive rewards or monetary incentives based on the dollar volume they generate or their equipment sales. So, while you are thinking that there’s no reason for a service mechanic to misinform you, there may be a very good reason to “shade” the truth – his wallet.

I’m not saying all mechanics worry more about incentives versus what’s right for the customer. Most mechanics are conscientious, honest, hard working people. But, between the inducements to sell equipment and the misinformation about carbon monoxide, there are a lot of furnaces being prematurely replaced due to questionable diagnostics.

Myths Make for Easier Sales

This is just one of a number of “myths” circulating in the HVAC industry. This kind of myth stops the customer from asking too many questions. It lets the companies in the HVAC business slip out from under potential liability by simply “condemning” equipment based on some vague notion that it is un-safe to operate. With everyone’s fear of carbon monoxide and cracked heat exchangers, no one really questions the practice.

And the Media Doesn’t Help

The myths have been reinforced by repeated exposure in the media, volumes of news articles, consumer protection information and even utility company policies. It does not matter whether the myths are true or false. Every contractor, code enforcement and safety organization operates as if they are true, so they must be true. Right?

They are WRONG about thousands of CO Deaths!

Another myth that’s perpetuated by the media and government agencies is the number of deaths caused by carbon monoxide poisoning each year. Some sources declare that “hundreds” are killed each year. Other media outlets use headlines like “Thousands Die Each Year Due To Carbon Monoxide.” Well guess what … they are wrong, totally wrong! Nobody checks their facts! They simply reprint what other agencies have published.

According to the Consumer Products Safety Commission, which has been tracking carbon monoxide related incidents for the last two decades, fatalities caused by carbon monoxide poisoning averages a whole lot less than what the media report! (It’s actually less than 100 people per year for gas furnaces.) I’ve got the numbers, straight from the CDC, to prove it.



Don’t They Care If You Are Left In the Cold?

I’ve stood in service meetings and posed this question to mechanics;

“If it’s the middle of winter with 20 degree temperatures and you checked a furnace and found a small hole or crack in a heat exchanger that was NOT creating carbon monoxide (CO), would you red-tag the furnace?”

Every mechanic, without exception, said yes, the red-tag was warranted and they would shut down the furnace.

Then I asked, “What about the family and the water lines in the house? The shut-down will cause a lot of inconvenience and may cause damage to their property if the water lines freeze.” There was usually silence. Then some wise guy would always pipe up with “we have to shut it down because of liability.” (In the back of the room you can see the company owners shaking their heads in agreement.)

Here’s the Big Problem

Nobody asked the question;

“Is the crack or hole causing a combustion problem?”

If there is no major flame disturbance or rollout or other operating problems, then the furnace is probably safe to operate on a temporary basis. It may have been operating for years with the hole or crack exactly like it is.

Come on – where is common sense?

How about a little compassion?

In the dead of winter we force a family out of their home, leave them open to potential damage because of water line freeze ups and use “liability” and “danger” and “the rules” as the excuse?

Did the mechanic at least use a CO meter to test the furnace to see if it was producing a high level of carbon monoxide before they shut down the heat?

It Has Been Happening for Years, Now Everyone Believes It

This find-and-condemn concept is so ingrained in the fabric of the business that I have had mechanics not believe their own eyes and test equipment when I tried to explain what was really happening inside the furnace.

The concern for liability issues loom large and are responsible for many of the policies adopted by code enforcement, gas utility companies and HVAC firms.

I don’t mean to imply that all furnaces with heat exchanger cracks or holes are OK to operate – even temporarily. Some should be shut down and red tagged. Any system with a large flame disturbance, flame roll out, concussive ignition or evidence of overheated wiring or components should be turned off and disconnected.

However, the majority of furnaces with heat exchanger cracks will operate for years without incident. Why throw a family out of their home by condemning their equipment in the middle of winter when there is no clear safety issue?

In the end, the consumer feels the pain with premature equipment replacement, misdiagnosed combustion problems and a lot of needless inconvenience.

Homeowners need to know what is safe to operate, and what should be avoided. Most homeowners have the power to minimize their risk from carbon monoxide poisoning once they understand what to look for. But, without the knowledge, it’s easy to fall prey to quick solutions and misdiagnosed equipment.

How Does This Affect You?

If you have a gas fired appliance, like a gas stove, or a gas water heater, or a gas clothes dryer, you are affected.

You need to be aware of what dangers your appliances can pose and what you can do about them.

Misrepresenting CO issues is done by “omission.”

There are NO direct efforts or conspiracies by any government agencies or safety organizations to misinform the public. It’s a case of only presenting part of the information, and is very similar to using a statement out of context. If you never find out the full story, you assume the information you’ve received is accurate. This is also how many of the myths about carbon monoxide proliferate.

I’m here to tell you that what you’ve been hearing about carbon monoxide issues is NOT accurate. You’ve only been hearing part of the story.



Next:  Myth #1 – Heat Exchanger Cracks