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Do furnace pros regularly check for heat exchanger cracks, and by what methods?

Do furnace pros regularly check for heat exchanger cracks, and by what methods?

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Old 03-02-08, 03:12 PM
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Do furnace pros regularly check for heat exchanger cracks, and by what methods?

Thought of this thread when I saw pflor's pic (on another thread near the top) on a scope used for checking?

I have seen many furnaces built where it does not seem like there is a real easy way to look into the heat exhanger area. So I was wondering if pros, when paid to do so, are likely really carrying out this job properly, and if they bother dismantling parts to be able to get in for a good look.

Do some of you pros care to share how you go about it on some of the makes of furnaces?
 
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Old 03-02-08, 03:55 PM
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I am not a pro yet but maybe someday. There are two methods I am aware of. The old style furnaces without combustion blowers can be checked by watching the flames. The airflow around the heat exchanger will cause the flames to dance if there are cracks in the chamber. On newer furnaces with combustion blowers there is a method where a chemical is sprayed around the chamber. With the chamber inlets blocked, the combustion blower will draw the chemical into the chamber and can be detected at the flew outlet using a refrigerant leak detector.
 

Last edited by tater1800; 03-02-08 at 05:20 PM.
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Old 03-02-08, 05:43 PM
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They have long mirrors for this!
 
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Old 03-02-08, 05:46 PM
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Heat Exchanger Cracks

There are several methods. I use an electronic combustion analyzer. If there is a change in the composition of the exhaust gases with the fan off & on, that is a good indication of a leak in the heat exchanger. When a change is detected, that is justification for pulling the furnace apart.
 
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Old 03-04-08, 09:16 AM
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airman,

have you used such mirrors and found with inserting a mirror way deep into the burner areas that you can actually tilt the mirror and see? I can't imagine how this could work. Wouldn't the mirror head have to be awfully small, and then the farther you hold it away from you, the farther it be hard to see? And you also have to get lighting in there also and not have the miurror block the lighting (unless the mirror you speak of has it's own light?). I have a telescoping mechanics mirror and there is no way you would always be able to get it in, here and there, and get the mirror tilted just right, that *I* can tell anyway.

Grady,

Is this method (you speak of) industry-backed as far as say if there were a lawsuit where someone was overcome with CO and they had hired a contractor to "inspect" the heat exchanger, that such a method, as the electronic analyzer method, would be backed up by the courts as being acceptable/equivelant to inspection?

I am wondering, that if say there were ever changes in negative pressure in a house, if during one visit everything might appear okay, yet there still could be a crack or hole in the exchanger that might be there and not produce any suspect reading due to how the pressure was at that particular moment, but may come into play under other conditions? Or, with at least the newer high efficiency draft inducer furnaces, is this impossible, where your test method is 100% reliable?

Based on what I said above, would perhaps the electronic analyzing methoid NOT be as a reliable a method on some of the older furnaces that simply updraft the flue gases out a chimney?, like say some of those old furnaces in mobile homes from the 60's and 70's? (and houses too).

tater,

I am thinking that what I said to Grady may have the same bearing with your method. Maybe the dancing flames will not always happen. In fact, I know they don't. I know of an older natural chimney venting gas furnace that has 2 heat exchanger cracks and there is no dancing when the blower comes on. (The person I work for has been informed of this and plans on getting new furnace in near future.) Up to 3 CO detectors have been placed in this house at different times and currently the readings are all 0, but one is still afraid, wondering if there could be some fluky change in house pressure, partial chimney blockage by some nest, or ?, that maybe that could change things.
 

Last edited by ecman51; 03-04-08 at 09:23 AM. Reason: added last paragraph
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Old 03-04-08, 10:47 AM
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Do furnace pros regularly check for heat exchanger cracks, and by what methods?

You can only do so much with mirrors because of the light and configuration. Often, you even have to dissasemble a portion of the furnace to get complete acces.

Dancing flames and sprays are only good for determining if there is a small leak.

There is no 100% test since a tight crack can open up quickly when the furnace is running even if everything was fine the day before.

There are many furnances that have a history of failures in certain areas and many HVAC people know what they are and where to look.

If you have an older furnace and are concerned. consider a newer high efficiency unit that will pay for itself quiclkly. The furnaces are getting so close to 99% efficient, waiting for improvement does not pay. the newer furnaces with the good variable speed fans will also decrease your AC costs and make everything more uniform and comfortable.

If you have a failure of your heat exchanger, it can easily be too later to do anything, because of the quick and fatal results.
 
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Old 03-04-08, 11:15 AM
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Wink

Like said you have to warm the furnace up some then check it for cracks . Then have to blower on can tell a lot You can still buy the old smoke bombs. They work. Might check on the PC and see what furnace heat exchangers have a recall on them. check this one.

http://www.furnaceclaims.com/
 
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Old 03-04-08, 03:16 PM
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HX Cracks

In the 5+ years I've been using the electronic instruments, I've never had it lie to me. A lot is knowing how to interpret the data. Numbers are just that, numbers. Knowing what they indicate is where you get what you pay for with a professional. With older natural draft equipment, readings have to be taken upstream of the draft hood. Often this means doing 4,5,6, or more tests, but only then can you get good data.
NO test method is 100% except complete disassembly & pressurization of the heat exchanger. If that is done, one could condemn a heat exchanger which is actually acceptable by government standards which allow a small amount of leakage.
 
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Old 03-04-08, 06:24 PM
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I'll get some info on the mirror for you.
 
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Old 03-04-08, 07:53 PM
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This all sounds like smoke (bombs) and mirrors, to me.

All info so far is interesting. Say more, Ed, about the smoke bomb test. Sounds archaic, but - effective?
 
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