Heat Exchangers... and carbon monoxide detectors, etc.

Originally Posted By: jwatts1
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Does anyone inspect heat exchangers or use carbon monoxide detectors as part of your inspection…


What are the best techniques for heat exchangers, or do you just not inspect at all? Correct me if I am mistaken, but most systems would have to be extensively dismantled for a full inspection..?

Please let me know....
thanks,
Justin. ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif)


Originally Posted By: kmcmahon
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With todays high efficiency units it’s all but impossible. But some of the older models you can sneak a mirror in and try to see what’s going on. I haven’t had much luck as there’s always too much crap in the way.



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Originally Posted By: pdacey
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I do not examine the heat exchanger. most of the time you can’t see it or you would have to dismantle too much to get to it.


I do use a CO detector. While the heat is running I go around to all of the registers and put the probe as close as possible to the register and take a reading.


--
Slainte!

Patrick Dacey
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www.southwestinspections.com

Originally Posted By: Gary Reecher
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The following information is gleaned from over 15 years as a residential HVAC service technician.


If you find co present in the plenum then the heat exchanger is defective. With that said you can also have a defective heat without having CO present in the supply plenum. So you can never say that a heat exchanger does not have a defect based soley on the absence of Carbon Monoxide.

There is no single method of inspecting heat exchangers. Think about it. Would you inspect a Pulse heat exchanger the same way as a clamshell heat exchanger , a clamshell heat exchanger the same way as a tubular heat exchanger ?


Types of Heat Exchanger Failures
1. Cracks.
2. Rust perforations.
3. Leaking heat exchanger seams.
4. Loose or missing screws securing cells.
5. Broken crimped rings
6. Broken or leaking seals or gaskets, including cemented seals.
7. Missing factory welds on seams.


Inspecting Heat Exchangers

1. Flame deviation test. Burner flame moves when the circulator blower comes on. If you do not locate a crack or perforation the heat exchanger seams can be leaking or the metal may have pinholes rusted through.

2. Visual inspection of burner chamber area and exterior of heat exchanger using a flashlight with high candlepower such a rechargeable Mag Lite.

Use a variety of mirrors. Small round and oval mirrors that have long telescoping reach are available at most welding supply stores. A large round mirror with long reach is also available through Sears.

For older heat exchangers have a mirror made at local glass shop 1/4" thick x 1-3/16" width x 24" length. A suitable carrying case can be made from 1-1/4" PVC pipe and fittings.

3. Water Spray Test.

Remove furnace blower assembly and the fan/ limit to prevent damage to these components. Spray the exterior of the heat exchanger with a water/soap solution 1 gallon water/ 1 tablespoon soap using a garden sprayer. Inspect the interior of heat exchanger with mirror and flashlight observing for evidence of water indicating a crack, rust perforation or crimp leak.

By shining a light on the outside or the inside of the heat exchanger area and examining the opposite side look for light penetration.

4. Measuring for CO in the plenum.

A CO detector cannot tell you if a heat exchanger is good. A CO detector can indicate a heat exchanger is cracked only if all of the following conditions occur simultaneously:

a. The flame generates enough CO (lack of oxygen, excess fuel, high temperature).

b. Enough exhaust gases are emitted from the heat exchanger crack or perforation.

c. The exhaust gases from the crack are not diluted too much before coming in contact with the sensor. A cracked heat exchanger may leak CO in a small stream. You may measure high concentrations only an inch away.

d. The heat exchanger is the only possible source for the CO detected.

Note: I have not tried this but have heard of some that will spray WD-40 or Gunk penetrating oil into the burner chambers (not the outside) of heat exchangers of furnaces with inshot burners to generate CO to see if CO will leak to the outside of the heat exchanger.

5. Combustion meter measuring undiluted flue gases.
One sign of a cracked heat exchanger is a change of oxygen concentration in the flue gases of greater than 1 / 2 % oxygen, or a change in the carbon monoxide level greater than 25 ppm. This change is measured by comparing readings before and after the circulation blower has turned on. For this test to be valid , CO levels must be present in the flue gas.

Check Bacharach's site Checking for Cracked Heat Exchangers
http://www.bacharach-training.com/Tips/Cracked.htm

6. The American Gas Association developed FURNACE HEAT EXCHANGER LEAKAGE TEST injecting a nitrogen and methane gas mixture into the burner chamber. The heat exchanger outlet of the heat exchanger is plugged and a combustible gas detector is used to check for gas leakage on the exterior. A detailed fact sheet on the AGA test procedure is available at
http://www.aga.org/pdf/publicinfo/codesstandards/twfacts8612b.pdf

Test Products International advertises the J&N Associates H.E.T. Kit and HXG-2 Combustible Gas Detector on their web site which does the above AGA test.
http://www.testproductsintl.com/gas.html


7. Magnehelic gauge test. Tape shut burner chamber openings and flue outlet. Connect magnehelic gauge to inducer pressure sensing port. Operate circulator blower. Movement of gauge needle indicates leakage into chamber.

8. Vapco H.E.A.T. Spray catalog number HT-1Q. Sprayed into the blower compartment on opposite side of motor. If burner flame changes color there is a leak in the heat exchanger.

Vapco http://www.vapcoproducts.com/catalogPDF/P19-outline.pdf

9. Magna Flux dye penetrant test. Using cleaner then penetrant and then cleaner over suspected area developer is then sprayed. Penetrant which has seeped into cracks, perforations or pinholes is pulled out by the developer agent. Full length of crack is seen not just what may be seen without theis test. Magna Flux cleaner, developer , red penetrant and zyglo fluoroescent penetrant is available through welding supply stores.

9A. Flourescent Dye with UV light inspection system from Visible Defects http://www.visibledefects.com/

10. Smoke Bomb test. Smoke bomb is placed inside burner chamber and lit. Evidence of smoke on the exterior of the heat exchanger indicates leakage.

10A. Smoke puffer test at the burner inlet and watching the smoke if it sprays away from the burner opening you may have a leak in the heat exchanger. [url] http://www.comfortinstitute.org/Brochures/smokepufferv2.htm[/url]


11. Camera systems can gain you access to some narrow openings and the inspection can also be taped for viewing by the home owner or for training. A couple sources for cameras are:

The Inspector http://www.shamrockindustries.com/home.html

IC Cam http://www.rotobrush.net/IC%20Cam.htm

Abatement Technologies http://www.abatement.com/residential/hvac_video.htm


12. Optical boroscopes can also get you access to some narrow openings. Yet do not offer the ability to tape the inspected areas.

Testoview http://www.testo.com/testoview.htm


13. Pressure Testing - Lennox Pulse Furnaces using kit part number 74K96.
Most failures on the Pulse occur at the solder joints at the condenser (secondary hx) outlet tube. However failures can occur at other areas[/b]


--
Gary Reecher, CM
HVAC Service Technician

MechAcc's Carbon Monoxide Site Links

Originally Posted By: kmcmahon
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Good info Gary. Thanks! icon_smile.gif



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Originally Posted By: Brian A. Goodman
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Whew! Info-heavy post Gary, good show. I tell my clients I can never see more than a little of the heat exchanger, but I look to see whatever I can see. Sometimes serious problems are plainly visible, sometimes you can see that it looks pretty good (though I never report that in writing, only problems). I’ve seen 'em with rust flaked off and piled high enough to cover burners, and with pieces of rusty metal loose inside them. For those reasons I look, but I don’t spend a lot of time on it and my contract specifies it as an “informational item only”.


I carry a low-level CO meter in my bag, which I set out at the property while I work. Twice it's gone off before I even got around to taking it out. The rest of the time it's on my wall at home, and I recommend it to all of my clients with gas appliances.


Originally Posted By: lkage
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Can always learn from a specialist.


Thanks, Gary


Originally Posted By: Gary Reecher
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A good LOW level alarm is CO Experts check http://www.coexperts.com for the information about this alarm. Less cross sensitive to household chemicals. Do a Google search for it and believe you can purchase them from an out fit called aeromedix.


Heat exchanger inspection classes. Try to get Ellis Prach from Heat Exchanger Experts to set up a class. He's a heating contractor from Colorado that will bring out over 50 different heat exchangers and furnaces different manufacturers and models. Go to http://www.heatexchangerexperts.com to see if there is a class schedule near you or to contact him to set up a class. He also has an inspection book with photos of typical failure areas for different model funraces and is updated annually.



--
Gary Reecher, CM
HVAC Service Technician

MechAcc's Carbon Monoxide Site Links

Originally Posted By: dhadler
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And don’t lay the hot spoon on a lino floor or something until it cools off.


The principle being... if the exchanger is good, the rotten egg smell will be taken out of the home via the chimney, if it has a hole or crack anywhere in it, the smell will be distributed into the living space via the heating ducts, just like CO would be. I still monitor for CO with a digital 4 gas detection unit as an addition back-up, but as you have already heard, there are many conditions that can cause false or no readings at all.

The test is very cost effective, quick to perform, and quite reliable. Most HVAC company's around here use it. The sulphur is available at Pharmacy Drug Co. and at some Veterinarian places. It's bright yellow in color, and can be in powder or pellet form. It's called Precipitated Sulphurand sells for ~$15. for a lb. which lasts a long time.

Hint: try and be quick if you have to pull the spoon completely out past the heat shield to get it into the next chamber, so you don't smell up the area your working in. It's pretty smelly stuff!

I'd be happy to tell you more on how to make the spoons if any one is interested. Have a great day! ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif)




Originally Posted By: phinsperger
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dhadler wrote:
I still monitor for CO with a digital 4 gas detection unit as an addition back-up


Darrell, what unit do you use?


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
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here !

Originally Posted By: dhadler
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It’s called a 4 gas detection unit made by RKI instruments Model #GX-2001 . It simultaneously detects LEL, O2,H2S and CO. It was quite high end and probably way more than was necessary, but it’s only about 2"x3" in size and has optional auto sniffer etc… it set me back a couple grand, but I really like it. Nice toy!


Originally Posted By: kmcmahon
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I’m sure the current homeowner would love the rotten egg smell throughout the home (tough to get rid of). On the other hand, it beats dying!



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Originally Posted By: dhadler
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Kevin,


I just started doing the sulphur test about 4 months ago, and I have not
come across a cracked exchanger yet, but from what I hear it's nothing a 15 minute airing out won't cure. But, your definitely right about the last half of your statement!!
And about the current homeowner...he's not going to be a happy camper anyway, finding out his furnace is going to need replacing. The smell will probably be the least of his concerns at this point.


Originally Posted By: dhadler
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Hi Ted,


Got your email. Your question, "could heating up the furnace to full operating temp actually close up any small cracks?


Reply, In theory that makes sense, but in the case of heat exchangers, most of the cracking occurs on the stressed portions of the metal. These are the spots that are shaped during manufacturing, rounded areas that are basically stretched when the metal is bent or formed. According to my friend whos been in the HVAC business all of his working life, the cracks in these stressed areas actually opens up when the metal expands because of the shape or rounding.

P.S. don't be afraid to ask a question on the forum, no matter how trivial it seems. We are all here to learn... we're in a learning industry, the more we share our experiences, the more we learn. I'm sure all my colleeges would agree; The time you get yourself in trouble is when you think you know-it-all! We can never know to much, that's why I joined NACHI in the first place. The forum is a great resource, I try to read it every day.


Originally Posted By: Brian A. Goodman
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[quote=“Gary Reecher”][b] A good LOW level alarm is CO Experts check http://www.coexperts.com for the information about this alarm. Less cross sensitive to household chemicals. Do a Google search for it and believe you can purchase them from an out fit called aeromedix.


I missed your post the first time Gary. That's exactly the one I use and recommend to all of my clients. I downloaded the brochure from their website in PDF. I print the first page and include it with the report on any house with any fuel-burning appliances. I've checked it against my $400 Monoxor II, and it's almost dead-on.


Originally Posted By: Kip Kale
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My Hallmark oil furnace was putting out a foul exhaust smell into my home. I havnt used a co detector, but i was pretty sure that co was coming in the house. I checked every visible thing i knew to check. After careful inspection i found the chimney was clogged with ash. i cleaned it all out and cleared the exhaust pipe. That seamed to help some, but i still smell and taste exhaust in my house. I understand that a cracked heat exchanger could be the cause, but what other possibilities could it be? someone told me that the ignitor could be the cause. I am no pro, please help!


Originally Posted By: jbushart
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Gary - A great post. I have a question for you based upon your personal experience in HVAC. How difficult is it for a pro to determine that a CO leak is caused by loose or missing screws securing the cells? It seems that this would be an inexpensive repair as compared to replacing the entire unit. Your thoughts, please.


Originally Posted By: Gary Reecher
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jbushart wrote:
Gary - A great post. I have a question for you based upon your personal experience in HVAC. How difficult is it for a pro to determine that a CO leak is caused by loose or missing screws securing the cells? It seems that this would be an inexpensive repair as compared to replacing the entire unit. Your thoughts, please.


Checking the screws attaching the heat exchanger cells to the furnace vestibule panel is just part of an HVAC tech's furnace inspection. However some furnaces such as ninety percent efficiency furnaces have screws that are located behind the vestibule panel and are not readily accessible for inspection and would require the removal of the heat exchanger assembly.


--
Gary Reecher, CM
HVAC Service Technician

MechAcc's Carbon Monoxide Site Links