What is your Method for checking for Cracks?

[OldSchoolMech]

So I was wondering how you resi guys look for cracks?In a heat Exchanger? What are the trade secrets or tools needed to make my life easier. I do alot of commercial id say 92% Commercial 8% Resi. Its easy to just look for cracks in RTU or Unit heater ( they crack alot) but besides from pulling the plenium and whole furnace apart what else is thier?

what about visible defects does this stuff work?


How do the smoke bombs work? Anyone got a vid of them using one?
Would a good Co2 Dectector pick up a leak at a register?

[crymtide]

cracks cause rollout in resi units which trips the rollout limit switch. So unscientific but easy. At the earliest stages a co meter will pick up the carbon monoxide but we rarely get called before the heat fails.

[Hvac216]

There's different ways based on what type of heat ex your dealing with. With ribbon type of upshot burners I prefer a simple inspection mirror. A match test with a telescoping wand also works. If the flame moves around a lot or goes out you probabaly have a crack. For a tubular heat exchanger a co test is good. High co and high oxygen with good combustion air and gas pressure is usually a crack. Also your obvious signs like rollout and yellow flames. Certain models are problematic too. Janitrols gmp from the 90's have a lot of bad heat ex.

[mark beiser]

Combustion analysis.
Watch the CO and O2 before and after the blower comes on, and as the HX heats up through the heating cycle.

You could spend an hour or more with an inspection mirror and a flashlight, or inspection camera, and never see a small breach in the HX, but 5 minutes with a combustion analyzer will let you know if there is one, even a tiny one.

[BigBacardi]

would a comb analyzer pick up a crack from a whisper heat?, that is not open, but cracked thru?

there is no one magic bullet formula.

i have found experience is best...and experience will still let alot thru.

knowing the guilty parties helps tons.....ie....whisper heat...90 % are cracked.

Goodman...gmp
bryant....394 gad....

most of these are cracked, but not all

[johnt2_2002]

As Bigbacardi said, experience plays a huge roll. You kind of know what to look for, where to look for it, and what to expect. I'm sure the same applies for commercial, I do 100% residential work...

But in general, i use a bright flashlight, mirror if required, and thorough visual inspection. If simple to remove a piece of sheet metal, I'll remove it and look at the HX, and while I'm there, evaporator coil.

If not, and space permitting, I'll drill a 1" hole in duct and use this-- http://www.dewalt.com/tools/cordless-instruments-inspection-cameras-dct410s1.aspx
Then its sealed with a rubber plug for a professional finish:).

Carbon monoxide readings can indicate problems, but its not always the case.

If I had a combustion analyzer, I'd use it the most, but I cant seem to get the boss to buy me one.......

[mark beiser]

would a comb analyzer pick up a crack from a whisper heat?, that is not open, but cracked thru?

Beats me, I haven't seen a furnace with a Lennox Duracrack HX still in operation in years. :p

I spotted problems using a CA that turned out to be due to some really small cracks.
It is important to monitor the full cycle from ignition on, and run the furnace long enough for the HX to fully come up to temperature. Dem cracks move a little at some point in the cycle, or they wouldn't be there. ;)

I still have and use an inspection scope, mirrors and HX smoke bombs, but the vast majority of the furnaces in my service area are 80% induced draft furnaces with inshot burners, which are ideal for the combustion analyzer method.

[kingkaiko2002]

I have to agree with everyone that experience does play a big role in finding cracks. Have you heard of the heat exchanger expert? Ellis prach. I would reccomend you buy his book and read it over 100 times. Typically when a heater exchanger cracks, it cracks at the weakest point. For example, most serpentine heater exchangers will crack on the outside bottom dimples. The only time I pull out heat exchanger is when I know it has a crack. That way I can show the customer and take pictures to cover my ass. Most of the time, they end up buying a furnace from me :-).

[Hvac216]

All very good points. It takes all the methods and experience to really do it properly. I'm not a big fan of cameras to find cracks, but they are usefull for selling furnaces.

[southshorejohn]

I use a combination of all of the above. With either my Insight or Testo 327 in the duct most will show up. Will add it's a lot easier if unit is oil fired between the diesel smell in ducts and wall streaks yep, I found the problem :grin2:

[OldSchoolMech]

Thank you guys for all the reply's I was just hoping for spme tips or tricks i geuss. I use all the said above methods.

Was hoping thier was something i didnt know

[MrPlumber]

It all comes down to your perspective, and experience. Usually if it is twenty + years old I go for the kill. I won't say I know every 'sweet' spot, but over time you develop some moves to make your life easier i.e. cutting out a 10" x 10" on the lower portion of a G20 - "Bag it and tag it". I guess you could say I am old fashioned, I use a light, a mirror, my fingers, and my eyes. Co detector are great tools, but don't just rely on it to tell you what is happening. In my area, we are required to give them the ppm reading when we red tag, so we can determine what type of hazard and the type of action is required. There you go, one tip to get you started.

[19degree]

Invest in a mirror and a good flash light. Lazy way is pulling the high limit and inspecting the top of the chambers down by the burners. You only get to see a portion of the HE so if you don't catch them there pull the blower and check each chamber 1 by 1. You'll find patterns after awhile carriers crack in the dimples goodmans in the burner ports and the rings comfort makers/International comfort always in the burner ports we call them money makers lol

[Glenn Harrison]

Here's an oldie but a goody thread with a bunch of different options for inspecting heat exchangers:

http://hvac-talk.com/vbb/showthread.php?t=72632&highlight=cracked+heat+exchanger

[ADillon]

For checking residential heat exchangers, there are alot of options. Combustion anylizer is gresat if you have it. If not here is a good method of checking. Of course it depends on the unit and type of heat exchanger...

-delta T across heat exchanger: If this seems abnormaly high, the unit may warrant further investigation.

-flame roll out: Upon start up, watch the flames coming off of the burners. When the blower starts up, there should be little to no deviation in the flame pattern. If there is then the blower is forcnig air through a breach in the heat exchanger

-remove high limit: Allows you to visually inspect many unit's heat exchangers. If the unit is running then any light visible through the limit opening is through a breech in the heat exchanger

-fiber optic scope/snake is a nice way to inspect heat exchangers

-A mirror or long rod that can be insterted down the burner tube and then 'drug' along the side to feel for cracks

-90% furnaces: Attach a manometer to the venting system/secondary heatexchanger or any other accessable area that is common to the heatexchanger/venting system. run the blower motor only and look for a change in pressure on the manometer. If the blower casues a change in pressure then there is a breech through which the indoor air is accessing the heat-exchanger. capping of vents is sometimes required if outside air is affecting the pressure inside of the venting system. This method can work for 80% as well but their vent systems are more likely to be affected by outside air movement.

use each check as a clue. If you don't have a high delat T or flame roll out, then you can prolly leave it alone. If you have have one or both, then proceed to the next check..use your best judgment.

[chaard]

Beats me, I haven't seen a furnace with a Lennox Duracrack HX still in operation in years. :p
.
We have plenty around here. Still replacing some hx's too.

To the OP, I use candle, mirror and my eyes. On janitrols I typically pull blower and look for crimp rings. If the pop off, they'll be in the blower housing.

Duracurves on whisperheats will crack high on the first bend.

I've used the dye method, but it is messy. It does work just not on serpentines or some Carrier hx. Their hx's are not sealed tight.