Originally Posted By: Scott Logan
This post was automatically imported from our archived forum.
I had my furnace inspected yesterday and two hairline cracks were found on two of the HEs. On many sites, and also according to the repairman who found the cracks, this will cause CO to leak into the house. He told me I needed to buy a new furnace, and seemed insistent on me setting up an appointment with is company’s sales rep.
Now, because money is tight, and he seemed somewhat pushy for a sale, and because I like to research things I looked up information pertaining to cracked heat exchangers. I found most sites did indeed support the premise that cracked HEs are a danger and cause carbon monoxide to leak into the heating system, and should be replaced.
However, I have also found some sites that say that this is myth - that failed combustion(or inefficient) causes CO, /not/ cracked heat exchangers.
The reason I fail to believe that a cracked heat exchanger would cause CO problems is that the inside of the HE is exposed to air already - what would it matter if the back side was also exposed? And even if that were a concern, as far as air being leaked in, the combustion is occurring almost 2 feet in front of and 10 inches below where the cracks occur - so how would it affect combustion and cause CO? I can see that cracks in the HE would perhaps cause inefficient usage of the heated air and cause loss of heat, but why would it cause a CO problem?
What is the real take on this? I hope to find some honest answers, as none of you are trying to sell me a new furnace, as was the repairman. 
I've also included the link for one of the sites that states that cracked HE's making CO is a myth:
http://www.contractingbusiness.com/news/article.cfm/newsarticleid/896
Thanks for any information and assistance!
Scott