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  1. #1
    Join Date
    May 2003
    chesterfield, michigan
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    There seems to be a few different ways of checking for a cracked heat exchanger and I was curious about which technique could be more effective than the other, asside from using a inspection camera, there very expensive and not everyone can carry one on there van, any input would be informative.

  2. #2
    Join Date
    Jul 2000
    NW IL.
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    For those that want one single never fail method for inspecting heat exchangers. There is none. 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 ? No you wouldn't nor should you. With equipment, knowledge and training you can become more proficient at inspecting heat exchangers.

    Types of Heat Exchanger Failures
    1. Cracks.
    2. Rust perforations.
    3. Over 50 percent of the heat exchanger wall thickness has rusted away.
    4. Leaking heat exchanger seams.
    5. Loose or missing screws securing cells.
    6. Broken crimped rings
    7. Broken or leaking seals or gaskets, including cemented seals.
    8. Missing factory welds on seams.
    9. Clean out port gaskets missing or leaking.

    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.

    Flexible lights are good for getting a light right on a suspected area. Flex-A-Light from Sears or the inspection light from SnapOn Tools Stock#: GA481B

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

    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. Large mirrors can be used for drum type heat exchangers.

    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.

    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

    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

    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.

    Part 2 follows

    Dadgum ole furnace.

    [Edited by MechAcc on 03-18-2005 at 03:30 PM]
    Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.

  3. #3
    Join Date
    Jul 2000
    NW IL.
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    Part 2

    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.

    Photo courtesy of the Baldloonie

    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.


    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. A flourescent dye spray and UV light test has been devloped by Visible Defects. The dye is sprayed on the exterior of the heat exchanger. The interior is then checked with the UV light. Picks up cracks, rust holes and faulty seams and welds. They also have a camera system. The lens head diameter is smaller than a dime.

    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.

    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

    IC Cam

    Abatement Technologies

    Visible Defects

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

    By supergluing a larger mirror to the Testo mirror you can improve the quality of the view.

    Be sure to properly attach the mirror. The mirror support should be on the side of the head that has the large optical opening. The two smaller openings are the lights.


    13. Pressure Testing - Lennox Pulse Furnaces using kit part number 74K96 available through Lennox.

    This kit comes with the pressure gauge fixture, plugs, instructions and a furnace wall patch plate. Additional patch plates can be ordered through Lennox. The carrying case and inlay is something I did on my own. Cases available through Sears.

    Most failures on the Pulse occur at the solder joints at the condenser (secondary hx) outlet tube. However failures can occur at other areas as the following photo shows.

    14. Global Leak Detection Corporation--- LeakChek Hawk pressure test kit. It can record and report using new industry standards in testing procedures as developed by Alberta Mechanical Officials Society . Click on products link.

    15. According to the Timken Silent Automatic Oil Burner Serviceman's Guide, 1926 Edition:

    A serviceman can easily check whether smoke is passing through the heat exchanger due to a crack is to shut off the burner and place a burning piece of TARPAPER in the combustion area. By then placing his nose next to a register if the smell of asphalt is detected in the home then there is probably a defective heat exchanger.
    16. Here's a test used in the land of natural gas, Alberta, Canada. It's called a sulphur test. We bring the unit up to full operating temp. then a small amount of sulphur is placed on a tiny collectors spoon which is fastened to a piece of soft 1/4" copper tubing about 15 and 22" long (I made 2 for different applications) and then inserted into the burner area. I let it burn in each chamber for about 15 seconds, moving it slowly back & forth, side to side. The amount of sulphur should do 3 or 4 chambers.NOTE: if you need additional sulphur, make sure you cool off the spoon in some water, or you'll have one stinky fire on your hands!! 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 Sulphur and 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!

    Want additional sources for heat exchanger testing and inspecting which include detailed methods and photographs of various heat exchangers showing locations of defects? Check the following.

    RSES Members check your SAM manual "Residential Gas Furnace Heat Exchanger Testing" Douglas DeWerth, P.E. American Gas Association Laboratories manual number 630-92 9/86. If you want a copy call RSES

    Contractor's Advantage

    Furnace Safety Consultant's http://www.furnacesafetyconsultants....0635/index.htm

    Heat Exchanger Experts

    Residential Furnace Heat Exchangers BOOK & CD-ROM

    Also a good book source for combustion and carbon monoxide testing "Carbon Monoxide a Clear and Present Danger "

    Training Classes

    Kansas City Building Institute

    Heat Exchanger Experts

    For those that are concerned only about carbon monoxide from leaking furnaces check this site about the toxicity of natural gas

    Dadgum ole furnace.
    Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.

  4. #4
    Join Date
    Nov 2000
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    Kudos MechAcc. What a detailed answer. Appreciate the time input for that.

  5. #5
    Join Date
    May 2003
    chesterfield, michigan
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    Thread Starter
    MechAcc thank you for all the information and it will all be used for future reference.

  6. #6
    Join Date
    Apr 2002
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    Great post mech, no wonder you find so many cracks
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

  7. #7
    Join Date
    May 2007
    Dry as a bone Tucson
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    Dad gum furnaces.......................
    "Christ is the Son of God Who died for the redemption of sinners and was resurrected after three days. This is the greatest truth in the universe. I die because of my belief in Christ."
    Watchman Nee

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