HEAT EXCHANGER
INSPECTION METHODS
Did I think up all these methods? No! But I did
actively search on heat exchanger inspection methods and the following are
methods that I found. 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.
Also check your local building codes. They may list further defects other than
the ones listed requiring heat exchanger or equipment replacement.
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 as at the top.
Jet engine mechanics use high candled power lights to inspect turbine blades and
illuminate cracks.
Flexible lights are good for getting a light right on a suspected area. Having a
light almost on the crack will highlight the defect. Flex-A-Light from Sears or
the inspection light from SnapOn Tools Stock#: GA481B
Sometimes you can even pickup odd looking lights such as this one that uses a
rechargeable Makita battery.
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. Use a male threaded cap for one end. Install a small piece of
foam such as rubatex in both ends. Tool plastic coating can be sprayed on the
back side for protection and at one end for a hand grip.
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.
A variation of the water spray test is the 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.
http://www.visibledefects.com
Don't eliminate the need to pull and fill a heat exchanger with water. Had to do
that once on a brand new secondary heat
exchanger to find that it had several leaking rivets causing the pressure switch
not to close.
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/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 of the heat exchanger. 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 the heat exchanger
either from cracks, rust perforations or leaking seals or gaskets.
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.
Vapco
http://www.vapcoproducts.com
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 this test. Magna Flux
cleaner, developer , red penetrant and zyglo fluoroescent penetrant is available
through welding supply stores. It was originally developed by the military and
has a mil standard labeled on the cans
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
http://www.shamrockindustries.com/
IC Cam
http://www.rotobrush.net/
Abatement Technologies
http://www.abatement.com/residential/hvac_video.htm
Visible Defects
http://www.visibledefects.com
12. Optical boroscopes can also get you access to some narrow openings. Yet do
not offer the ability to tape the inspected areas.
The above photo is of the original Testoview. Check out the newer model 318
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.
Testoview
http://www.testo.com/testoview.htm
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 available in a pakage of 5
using part number 16L98 can be ordered through Lennox. The plugs can also be
used to block off standing tees on air conditioning drains so you can use a
sludge sucker at the drain end to clear plugs.
The carrying case and inlay is something I did on my own to protect the gage
assembly as well as provide quick inventory to insure that plugs are not left
behind. This case was obtained 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.
http://www.gldcorp.com/
15.Here's an old timer's method for oil furnaces. 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 that is recommended by someone 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!
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 to buy a copy call RSES (800)297-5660
http://www.rses.org
Contractor's Advantage
http://4youradvantage.com/heatexch.htm
Furnace Safety Consultant's
http://www.furnacesafetyconsultants.com
Heat Exchanger Experts
http://www.heatexchangerexperts.com
Residential Furnace Heat Exchangers BOOK
http://www.inspectiondepot.com/Catalog/product_detail.php?PID=84
Gas Appliance Service Training and Consulting, 22 Griffith Drive, Riverside,
Rhode Island 02915 phone 401.437.0557
Also a good book source for combustion and carbon monoxide testing "Carbon
Monoxide a Clear and Present Danger "
http://www.escoinst.com
Training Classes
Kansas City Building Institute
http://www.kansasbuildingscience.com/inspect.htm
Heat Exchanger Experts
http://www.heatexchangerexperts.com/photos.html
Carbon monoxide is not the only thing to be concerned about from furnaces. Check
this site about the toxicity of natural gas and other toxins.
http://www.geocities.com/RainForest/6847/report1.html#6.0
Bottom line is never stop thinking you may think of a better way to test and
inspect heat exchangers.
Gary Reecher, CM