Cracked Heat Exchanger

[John Allingham]

I have a couple of furnace questions that I would appreciate some help with:
(1) Is it possible to have CO leaking from a cracked heat exchanger on a high efficiency furnace? The induced draft fan keeps the H/E interior at a negative pressure. It seems to me that this would cause air to leak into the H/E rather than gases to leak out.
(2) For a standard efficiency furnace, have there been any fatalities caused by a cracked H/E. I did some research in Canada and couldn't find any. There have been numerous CO related deaths due to blocked venting, cars left running in garages, barbequing indoors, etc but none that I can find due to a cracked H/E. Has there been any documented cases in the US?

[gbeaumont]

(1) Is it possible to have CO leaking from a cracked heat exchanger on a high efficiency furnace? The induced draft fan keeps the H/E interior at a negative pressure. It seems to me that this would cause air to leak into the H/E rather than gases to leak out.

Hi John, I believe that Co can still easily be drawn into the supply air due to the venturi effect within the plemumn, the draft fan does not produce a huge ammount of draft.

(2) For a standard efficiency furnace, have there been any fatalities caused by a cracked H/E. I did some research in Canada and couldn't find any. There have been numerous CO related deaths due to blocked venting, cars left running in garages, barbequing indoors, etc but none that I can find due to a cracked H/E. Has there been any documented cases in the US?

John I am not aware of any deaths associated with CO from this sourse however I have personally know of 2 instances of sickness caused by this issue, IMHO death is a real possibility.

Regards

Gerry

[bkelly1]

Here are a couple I found in the last couple of weeks.

[Patrick Bolliger]

One factor that we should all keep in mind is the possibility that most "older" homes are not as "air tight" (windows/ doors/ walls) as newer homes with high efficiency cat 4 condensing units. You have to also consider the possibility that CO detectors and areas of the country that do not rely on gas / propane heating as much also affect statistics. Older homes in heating areas like in my area (midwest) have more Cat 1 natural draft units installed in basements, enclosed basements and closets where CO generation is more likely then cat 4 high efficiency units with combustion air coming from the outside via PVC piping. This is not to say that all sources of CO come from your FAU. The kitchen range, water heater, garage (car) and some space heaters, fire places are other sources..

So what does my city do? Tell everyone to get a CO detector! Save lives! Doesn't take away the fact that "their" installation is potentionally dangerous but to have a warning when the concentration is in the range of the EPA or other governmental organization that sets standards states so.. Deaths occur every year around here..

Check UL, insurance companies websites like State Farm and you should find numbers..

[jrupert]

Yes it is possible to have carbon monoxide leak into the home from a heat exchanger in a inducer draft fan furnace. The pressure with in the heat exchanger is still greater then that out side it until the blower kicks in and even then the risk of pulling C02 in to the house air is present.

Yes deaths have occurred here just a few
http://www.dailystandard.com/date/2006/03/02/news/headline2.htm
http://www.carbon-monoxide-poisoning-injury.com/news.htm
http://www.homesafe.com/coalert/cofacts.htm
http://www.coheadquarters.com/COEpidem/coepidem02.htm

[Russel Ray]

Here's one from About Homes. It is the best web site I've found for current news on CO deaths and injuries. They update it on a daily basis.

INF-0179

If that site doesn't make one sit up and take action, nothing will.

[David P. Valley]

Here's a very informative thread that was posted last year...
Attachment 2022

[John Allingham]

Thanks everyone, but unless I missed it, none of these deaths were directly attributed to a cracked furnace heat exchanger. Please repeat the link if I did miss it. Thanks again.

[Russel Ray]

INF-0179

I know there is at least one because I found it over there before. That was last December that I was looking. Their list is very extensive and you have to have a lot of time to read through every post to find that one item.

[Dean Call]

First of all furnaces do not produce CO, they produce CO2.
IF they are burning properly and getting ample make up air.
Secondly, a crack in a heat exchanger can't let hardly any gases pass through because the opening is so small plus the pressure from the blower is much greater then the pressure inside the heat exchanger. (assuming "crack" doesn't really mean "large hole")

That's not to say that a cracked heat exchanger is not potently very dangerious because it is.
As an example, say the flue starts dumping CO2 in the furnace room for whatever reason and rather than good clean make up air, the CO2 starts getting drawn in, mixed with the fuel and gets burned in the place of oxygen, the second time through the burning process produces CO.

That same thing is what happens when there is not enough makeup air at the furnace or the flue is not drawing.

[Russel Ray]

Originally Posted by Dean Call

First of all furnaces do not produce CO, they produce CO2.
IF they are burning properly and getting ample make up air.

That's a dangerous statement, even with the "IF."

Anything that burns organic fuel (such as wood, oil, gas, etc.) will produce carbon monoxide because it is a natural byproduct of the burning process. The only time that carbon monoxide would not be produced is if a system were 100% efficient. And 100% efficiency doesn't exist on this earth outside of a laboratory, and I'm not sure that it exists in a laboratory either.

I think a Google search and a day's worth of reading is in order.

[Gary Reecher]

First the Gas Research Institute 3 point inspection method states in their first step. Visual inspection: any visible crack requires replacement of the heat exchanger or the furnace.

In spite of the claims that a negative draft induced furnace will not allow carbon monoxide leak out I have found a couple of the exceptions. In spite of engineering claims nothing is 100 percent. A furnace heat exchanger is a curved surface air flowing across such surfaces can do some mighty strange things. One instance I wished I had a video camera. A visible crack above a burner section. Yet when the circulating blower came on rather than the flame blowing away from the crack it floated right up into the crack. Seeing that will happen make believe anything is possible.

[John Allingham]

Originally Posted by jrupert

The pressure with in the heat exchanger is still greater then that out side it until the blower kicks in and even then the risk of pulling C02 in to the house air is present.

Hi John
On my high efficiency furnace, the induced draft blower kicks in sometime before ignition. Therefore the H/E will be under negative pressure anytime the gas is on. Aren't they all like that?

[Gary Reecher]

Originally Posted by jallingham

Hi John
On my high efficiency furnace, the induced draft blower kicks in sometime before ignition. Therefore the H/E will be under negative pressure anytime the gas is on. Aren't they all like that?

Most but not all. Comfortmaker at one time had one model of their furnaces that had a combustion air blower blowing air into the burner box. Rheem Ruud roof top units also use a small combustion air fan that blows air into the burner box.

As I stated in the heat exchanger inspection methods: One method does not fit all furnaces. You have to choose the inspection method for the type furnace and heat exchanger.

[jrupert]

1). Furnaces using a draft inducer are still injecting large amounts of gas and air into the heat exchanger (around 30 cuft of air per 100,000btu of gas) this neg pressure is relative to the air around it and it is still at times greater then the air out side the heat exchanger and it will leak This is a serious and dangerous issue, leaks / cracks are dangerous. No matter what type of furnace.

The issue is when the blower kicks in and introduces additional air into the heat exchanger through the crack, that combustion is effected and the possibility of carbon monoxide exits,.

2). Furnaces that are operating normally will produce Carbon Dioxide, when combustion is effected so it is not burning properly they it can produce Carbon Monoxide. A furnace with a crack may burn clean and not produce C02, but it still must be replaced.