If there is CO getting into the home, the crack is the least likely culprit. In fact it is right up there with winning the lottery, just about impossible.
I agree the crack isn't the cause of CO developing... CO is caused from unburned fuel... The reason for the unburned fuel is what needs to be addressed. However, If you mix the two together the homeowner is looking at a very large expense as a hole or crack is definately a compromise and I don't know about you but I don't want my company liable by leaving a compromised HX in someones home and just fixing the reason for the unburned fuel... Just my honest opinion.
Uh, I gotta ask. So if you all agree that a crack in the heat exchanger doesn't pose a CO threat,
then what's wrong with a crack in the heat exchanger? Please explain the "compromised".
If it is all about some future threat, what threat is that and how long realistically before
that threat would appear?
(I'm lurking, not arguing. All of this is unfortunately new & puzzling stuff to me.)
Wait. I have a contribution.
On another thread, "where can I find west coast combustion analysis training?", I found
a link to a 52 page PDF on Testo's website. On page 28, it talks about finding heat
exchanger cracks and agrees that CO analysis won't change, but rather O2 levels
will, or might. Fascinating stuff.
So here again is the link: http://www.google.com/url?sa=t&rct=j...nOAgyjFgEodNXw
George the issue boils down to liability. Since none of us have a crystal ball and we can't tell when that crack is going to split open it's a CYA thing.
When they do open enough to disrupt the flame large amounts of CO can be produced,soot forms causing the cell to not vent correctly and the CO then spills into the home. I recall one like that two winters ago. New customer that called because the CO detector was going off. They shut the furnace off then called us. I got there and fired up the furnace first to see if it was the source of CO and my analyzer showed 800ppm spilling out the front of the furnace yet the roll out switch was not tripping. The top of that cell was 100% blocked with soot and there was a crack that must have opened up as the exchanger heated.
A cracked heat exchanger can be a bad situation. But with the newer furnaces that are essentially negative pressure, is there any harm? Today I found a heat exchanger, 16 years old, very rusty on the inside with seems that are 1/8 to 1/4 inch separated. No indication of a crack, but it made me nervous just looking at it. I brought the customer down to the furnace and explained that although I could not find a definitive crack, my gut feeling is that if I pulled the furnace out, I would find one. I used the bore scope and could see signs overheating. I red tagged it.
Questions. How far do you go to find a crack if you suspect one? What do you let go?
We have guys at my company that will actually pull the h/x to show a customer a crack or rust hole. I personally just look with my camera and show the customer, explain there is no way of knowing when it will rust through and that I won't be there everyday to check. If its really bad its better to red tag it and cover your butt .
Last crack I found was just last Friday and it was as hairline as you can get while still producing resistance when dragging a wire across it. I brought them both down and showed them how I shut the gas cock, turned the gas valve off and left the disconnect off. I fully explained to them the possible dangers of reversing my actions and ignoring the red tag. I also explain how CO is produced (incomplete combustion) and that a crack in the HE will not necessarily produce CO.
The reason I take these steps? Simple. As this and multiple other lengthy threads in this forum (I spent most of the day reading them) and others clearly demonstrate: We as an industry haven't a clue as to WTF we are doing when it comes to this particular issue. My method demonstrates the best possible compromise I can negotiate between all I read. My company is covered and I am protecting my customer in as much as they will let me.