Originally Posted By: kelliott This post was automatically imported from our archived forum.
Haven’t heard of it. Do you know how do you use it? How do you find a cracked in a heat exchanger where you can’t access it, with a spray bottle of liquid?
Originally Posted By: dbowers This post was automatically imported from our archived forum.
Some old time HI’s and HVAC contractors drill a hole in the sheet metal case housing the evaporator coil and spray a solution of mineral oil and water in there. About 15-20 minutes later they look for signs of moisture in the HE area. If present the HE has cracks, holes, etc.
This may be similar substance in a pre-mixed formula.
Originally Posted By: ssopha This post was automatically imported from our archived forum.
To use H.E.A.T, spray the stuff into the return intake of the HVAC and watch the flame pattern, if it changes you have a crack in the heat exchanger some where. Supposedly the change is very noticeable if cracks exist.
Originally Posted By: kelliott This post was automatically imported from our archived forum.
hmmm, drill a hole thru the plenum, and inject this material into the area, and hope it somehow migrates underneath the coil condensate pan, and runs down around the heat exchanger and thru a hole, which is most likely going to be in a seam at one end or the other of the heX. Is that the gist of it?
I dunno. Having seen several styles of heat exchangers up close and personal, I can't believe that would likely be very accurate, when you consider the twists and turns of a heat exchanger. And if its not accurate, what's the point? I might as well just report that it looks good to me, and PROBABLY isn't leaking. Or, I could say, don't see nuthin, so I'm bettin, there's nothing to worry about...! 
I basically use the 3D disclaimer statement for all heX which basically says, [extreme paraphrasing] no possible way to see it all, so can't tell you one way or the other. Call a HVAC expert and let them stick their neck in the noose 
Or is that the chicken way out? I just can't see me pulling a drill out of my bag and popping the furnace full of holes to do that test. Do you know inspectors who do? I'm really curious about this now.
Originally Posted By: kelliott This post was automatically imported from our archived forum.
Oh, Souksana your reply came in while I was typing mine. So it is injected into the Return air, so it flows past the HeX and supposedly is going to be sucked into the burn chamber and makes the flame go squirrely. That sounds better than drilling holes in the furnace, but still, I’m skeptical. If that hole is in the top of the HeX tube, it seems to me the air movement rushing past the HeX wouldn’t let it pull back down into that heat chamber, so it would lie to you. On the one hand, you’re doing the client a service by informing them if you DO find a leak, but if you do the test and it fibs, then it seems to me you’re on your way to trying out your E&O. when the family takes your word for it that the furnace was safe, and wake up dead a week later from Carbon Monoxide. It would make me vewy vewy nervous. I think I’ll stick with the disclaimer.
Originally Posted By: ssopha This post was automatically imported from our archived forum.
Keith,
I would also test CO in the house if I do find that the HeX have a crack. As an HI, I know that I am going above and beyond the SOP to make my client happy. As you said I am testing my E&O, maybe I should just stick with my disclaimers and move on.
If you don't mind me asking, do you just disclaim about the possibilities that the cracks may exists and move on or do you do some kind of test?
Originally Posted By: Blaine Wiley This post was automatically imported from our archived forum.
On the rare times I see a gas furnace, I add this note in my report:
NOTE: Without removing the burners to gain complete access, and with the limited viewing area of the heat exchanger, a thorough inspection is not possible. The visible portions of the burn chamber and heat exchanger were rusted, but there were no visible holes or cracks at the time of the inspection.
I've seen two gas furnaces in the past 14 months. The flames tumbled badly when the blower started on one of the, and yepper, it had a cracked HE.
Originally Posted By: Brian Wesley Jamison This post was automatically imported from our archived forum.
I know that there are various signs an inspector can look for when inspecting a heating unit for cracks, such as, flame rollouts when the air handler comes on and Co in the ambient air. In my training manual it states that another good indicator for this, on fan assisted units, is to watch for a change in O2 with a combustion analyzer when the air handler comes on. My question is, will this work for an atmospheric unit as well?
Originally Posted By: Rich Clos This post was automatically imported from our archived forum.
There are two things to remember about cracked heat exchangers,
One. Some cracks allow the conditioned air blower to create a negative pressure in the exchanger, thus it sucks out fumes into the air stream
Two, some cracks create a 'possitive' pressure inside the exchanger.
This is why the Oxygen level on a furnace will increase with a crack that allows air to blow INTO an exchanger.
Years past we would use salt water and spray it into the heat exchanger while it was running. Somewhere down the path of supply air a halid detector, an instrument used to test for refrigerant leaks would be used. If the flame turned yellow you had a 'sucking' leak and the exchanger had a crack. Not very reliable to say the least.
Visual inspections on exchangers isn't even proof possitive that you don't have aleak. It only takes a pin head on a five ton blower to poision a family over a period of time.
Flame movement and change in color etc is a good indication of a 'possitive' leak. Also, a mirror on the draft diverter will help show a possitive leak with slight spillage.
A pressure testing instrument for flues will work with a sealed combustion unit. If the pressure changes when the blower comes on it is a suspected exchanger problem.
Smoke tests have been used, and other system. ASHRAE has approved methods and equipment, but I can't afford them!
Originally Posted By: Lee Rohlf This post was automatically imported from our archived forum.
Visible Defects claims they have a system for locating even the smallest heat exchanger cracks.
The system uses an ultraviolet dye along with a UV spotlight. A flexible cigarette wand camera can see into and record for customer viewing the damaged area.
Originally Posted By: Trevor This post was automatically imported from our archived forum.
I bought a house and had a licensed gas tech come out to clean the unit. It’s 17 years old and the HI said I probably have a couple of years left on the unit. He said it needed a good cleaning due to yellow flames.
Well the gas tech came out and tested the heat exchange by lighting a wick and placing it in the chambers. 2 out of 3 chambers kept the flame, but the 3rd would cause the flame to flicker and in some cases blow it completly out, near the front of the chamber. He then concluded that the HeX was cracked.
Is this a good way to check for cracks? It seams kind of primitive and I thought he might have some kind of tool to detect a leak. Any input would be greatly appreciated.
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:
Originally Posted By: jpeck This post was automatically imported from our archived forum.
Scott,
As long as you are willing to BET YOUR FAMILY'S LIVES on NOT replacing them, nothing anyone can say will dispel your unwillingness to spend the money, because money is tight.
I suggest you answer your inquiry this way: If money was not tight, would you replace them for safety's sake?
If your answer is no, there is not much we can do or say.
If your answer is yes, then the cost of replacing the furnaces is the monetary value you are placing on your family's lives.
I have tried to reduce it to the simplest of terms, in the terms you are using - $$$$$.
Originally Posted By: rrushing This post was automatically imported from our archived forum.
Think of a heat exchanger this way…
The combustionable gas has to be separated from the warm air entering the home. A heat exchanger serves that purpose, which is usually nothing more than just a piece of sheet metal.
The two sides of the sheet metal separate the exhaust air combusted by the burners and on the other side is the fan blown air that enters the home. Now, if you have a crack in the heat exchanger, guess what... you now have unspent/ unburned gas entering the fan blown air and distrubuted throughout the home for all to consume.
J.Peck put you on the right thought process... If you can't afford to do it now, think of your survivors, if any... Will they be able to afford it after you (or they too) are gone?
Originally Posted By: Scott Logan This post was automatically imported from our archived forum.
It’s not unwillingness to spend money for my family, it was to do so when there seemed doubt as to whether a cracked HE would /actually/ cause a health threat. Many interent sites suggested that it would not, and therefore why would one spend money on something that is not a threat?
By what you've explained, there is and as such has convinced me of the need to replace the furnace. Unless there is a known patching material you could use to repair any cracks. I'm capable of removing and replacing the panelling/insulation of the furnace and now that I know what to look for, could easily locate any cracks that do/might exist and repair them if there exists a sealing material suited for the job. Any suggestions?
I thank you guys for the explanation as the fellow Ihad in for the cleaning/repair wasn't all that informative. 
Originally Posted By: jpeck This post was automatically imported from our archived forum.
Scott Logan wrote:
if there exists a sealing material suited for the job. Any suggestions?
None that I am aware of.
Plus, the cost (if paying someone to do it) and effort (either for you or them) to get to the heat exchanger, and to button it all back up afterward, is most of the cost and effort.
The actual cost of the heat exchanger itself is not that much.
We have very few gas furnaces down here, but I've been told that the cost and effort to replace a cracked heat exchanger is better applied to a new furnace if the furnace is very old at all.
Anyone more familiar with this please add your comments.
