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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.

Originally Posted by trouble time

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 .

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.

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

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.)

Originally Posted by chuckcrj

The ones with cracks.

I'll have to pull the readouts of the combustion analyzer tomorrow, I'll let you know though.

Originally Posted by chuckcrj

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.

Originally Posted by JonesHVAC-R

For which?


.

The ones with cracks.

Originally Posted by chuckcrj

What were the CO levels in the flue?

For which?

Originally Posted by chuckcrj

Carbon buildup? That is just a symptom of a larger problem.

I agree, the furnace was 20+ years old and in a rental unit so I just recommended an upgrade to the landlord who agreed that would be most cost effective.

Originally Posted by JonesHVAC-R

Actually, out of 4 calls this month I had 3 homes reading anywhere from 3-9ppm and 1 reading above 20ppm(shut furnace down before it got any higher). Out of those 4 two had cracked HX's. The one with 20ppm+ was carbon build up in the HX and the exhaust, customer upgraded anyway. The last one had a bad inducer assembly.

What were the CO levels in the flue?

Carbon buildup? That is just a symptom of a larger problem.

Originally Posted by bigtime

Has anyone anywhere found a home with carbon monoxide in the living space, and the cause was a small crack in the furnace heat exchanger? If so Id like to hear the details.

On any residential co problem, Id put my money on a vent problem. Spend more time inspecting vents...

Actually, out of 4 calls this month I had 3 homes reading anywhere from 3-9ppm and 1 reading above 20ppm(shut furnace down before it got any higher). Out of those 4 two had cracked HX's. The one with 20ppm+ was carbon build up in the HX and the exhaust, customer upgraded anyway. The last one had a bad inducer assembly.

Originally Posted by JonesHVAC-R

Are you saying that if a heat exchanger is cracked that CO will not get into the home?

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.

Another question. Has anyone anywhere found a home with co in the living space and it was casued by a gas pack?

Has anyone anywhere found a home with carbon monoxide in the living space, and the cause was a small crack in the furnace heat exchanger? If so Id like to hear the details.

On any residential co problem, Id put my money on a vent problem. Spend more time inspecting vents...

Originally Posted by chuckcrj

If the furnace is spilling CO and causing house levels anywhere above zero then yes new is the first choice. Usually there is a repair option as well if the HO can't afford new. (unless the HX is cracked, which is almost never the cause of CO getting into the home)

Are you saying that if a heat exchanger is cracked that CO will not get into the home?

Originally Posted by martyinlincoln

Got a perfect example of why that's important today. Lennox G20 that another company replaced the heat exchanger last year. It had the typical stress mark and rust line along the back but passed water test. Cleaned the burners,crossovers,pilot assembly and flame sensor then put it back together to get some flue gas readings. Stuck the probe in the flue and had 4.2% O2 and over 9000 ppm of CO,I know should have pulled the probe out way before that to save the sensor. Gas valve was cranked all the way in and reading 7.2", backing it out didn't change the pressure. Installed a new gas valve and made a new sheet metal flange that the bone heads left out. CO 14ppm with 7.2 O2 after fixes.

7.2"!! I had a tech once turn one down to 2" while I was away... I got back and asked why so low and he replied that is where it needed to be in order for the burners not to snuff out... Not quite sure what the hell he was thinking there... I told him to come with me and it turned out they weren't snuffing at all but they cutting out from the rollout sensor. Old Bryant 80% rooftop unit with just about everything rusting... gave them the option of repair or new unit, they took the new unit

Originally Posted by JonesHVAC-R

Curiousity getting the better of me..... how many of you use a CO meter (calibrated before entry to home) while doing clean and checks?

Got a perfect example of why that's important today. Lennox G20 that another company replaced the heat exchanger last year. It had the typical stress mark and rust line along the back but passed water test. Cleaned the burners,crossovers,pilot assembly and flame sensor then put it back together to get some flue gas readings. Stuck the probe in the flue and had 4.2% O2 and over 9000 ppm of CO,I know should have pulled the probe out way before that to save the sensor. Gas valve was cranked all the way in and reading 7.2", backing it out didn't change the pressure. Installed a new gas valve and made a new sheet metal flange that the bone heads left out. CO 14ppm with 7.2 O2 after fixes.

Originally Posted by chuckcrj

A rusted heat exchanger is not a failure if there is no "visible crack or hole".

What type of heat exchanger is it? When you open up the supply duct and look at it are the seams folded and welded. Because those particular H/E are tanks and seem to last. With a bore scope through the burner section they look cracked but indeed they are not.

I agree no visible crack or hole = No red tag

Originally Posted by JonesHVAC-R

Lol, I agree there! Leads to my next question...

How many of you when entering home and get a reading anywhere from 1-6ppm recommend replacing the furnace right there? (assuming the CO is coming from the furnace during operation)

If the furnace is spilling CO and causing house levels anywhere above zero then yes new is the first choice. Usually there is a repair option as well if the HO can't afford new. (unless the HX is cracked, which is almost never the cause of CO getting into the home)

lol...loaded question

but yes... i do carry my co detector into every job.....responses from homeowners vary, but most are impressed