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Condensing Gas Furnace Inspection
CO Gas Leak Test Procedures
- POST a QUESTION or COMMENT about furnace heat exchanger leaks, cracks, damage, inspection & testing
Inspection & tests of a condensing gas furnace:
Visual inspection of a 1996 Tempstar™ condensing gas furnace discovers signs of "reverse air flow" at the condensing furnace air intake. This condition leads home inspector Roger Hankey to expand the inspection scope to test the heating system for safety.
Page top photo: initial inspection at the top of this Tempstar™ gas furnace shows discoloration at the combustion air intake, a possible sign of improper and unsafe system operation discussed below.
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Condensing Gas Furnace Inspection, Tests, & Carbon Monoxide CO Gas Hazards
Furnace inspection leads to recommended test
On a 20˚F day in December 2017 an initial tour of the house found a condensing gas furnace in the basement with a plastic vent pipe and no pipe on its air intake.
A plastic grid over the combustion air intake was discolored and cracked consistent with heat damage [photos above].
[Click to enlarge any image]
Also a very slight odor was found at the intake consistent with the odorant in natural gas.
Opening the front panel revealed corrosion consistent with condensate leak below the inducer but no active leak was found.
2018-01-15 The original draft of this article remains under discussion.
See the working document
at CONDENSING GAS FURNACE INSPECTION & TESTS DISCUSSION
Also see the procedures discussed at HEAT EXCHANGER LEAK TEST - Editor.
Question: how long should my gas furnace last?
what is the normal life of natural gas furnace? - Marlin 10/30/12
Reply:
Just about the warranty period - manufacturers know their equipment well; warranty periods run from 10 years to "lifetime"
Please see FURNACE HEAT EXCHANGER LIFE where we give details about residential heating furnace life expectancy.
Question: why does the pilot flame keep going out on my hot air furnace?
What would cause standing pilot flame to keep going out . thermocouple was replaced hoy air furnace - Bruce 11/17/12
Reply:
Bruce,
Check for these other causes of loss of the gas pilot flame
- A bad replacement thermocouple or one that was bent, kinked, damaged during installation
- Thermocouple not properly connected at the control, e.g. the sensor connector not fully screwed-in
- Thermocouple sensor tip not properly mounted, secured in the flame path
- Sudden drafts
- Low gas pressure, weak flame
- Inadequate combustion air - very dangerous, can be fatal
- Dirt on the equipment
- Something else we haven't thought of
- See THERMOCOUPLE REPAIR / REPLACEMENT for details
®Roger Hankey & InspectApedia.com 2018
Roger Hankey is principal of Hankey and Brown Inspections, Winter Park, CO. Mr. Hankey is a past chairman of the ASHI Standards Committee and served in other ASHI chapter and national leadership roles. Mr. Hankey is a National Radon Proficiency Program certified measurement professional and a Level II infrared thermographer. Contact Roger Hankey at: 970-393-6604 - rogerhankey47@gmail.com . Website: www.HankeyandBrown.com Mr. Hankey is a frequent contributor to InspectAPedia.com.
Reader Comments, Questions & Answers About The Article Above
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Reader Q&A - also see RECOMMENDED ARTICLES & FAQs
On 2020-10-16 by (mod) - clearance between a direct-vent for a gas fired heater and an operable window.
Karottu
Thank you for the helpful photo and question about clearance between a direct-vent for a gas fired heater and an operable window.
The guidelines for clearance distance from the gas vent outlet to the closest edge of an operable window (or door) vary by country.
In the U.S., depending on the BTUh rating of the heater, you need typically 12" but as much as 36" of distance.
In Canada the specifications for gas vent to window are:
6 inches (15 cm) for appliances =/< 10,000 btuh (3 kw),
9 inches (23 cm) for appliances > 10,000 Btuh (3 kw) and =/< 50,000 btuh (15 kw),
12 inches (30 cm) for appliances > 50,000 Btuh (15 kw)
So you'll want to identify the brand and model of your specific heater and to see what the manufacturer requires.
Please see details at GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES
About the distance between the gas-fueled heater direct vent exhaust opening and intake opening, your photo looks typical - instructions often specify a 12-inch separation (or more) between intake and outlet openings;
but again you'll want to see what the specific installation instructions for your specific heater require.
On 2020-10-16 by Karottu T. George
Recently installed a Carrier furnace 59TP6B040V14-10. The venting is a 2 pipe system as shown in the attached picture. The exhaust vent is about 2 feet just under a bedroom window and about 1 foot from the basement window directly below. Is this a health concern for the person in the bedroom? The vent is directly under the window (though 2 feet under).
Also, is it possible for the exhaust gases drawn into the furnace through the inlet pipe. They are both very close together..
Question: is it possible to temporarily patch a leaky furnace heat exchanger?
I have a rooftop unit and have been told i have a few very small holes in the heat exchanger that can be repaired with an appropriate silicone which should hold for a season or two. True? Thanks.
Reply:
Tom,
You may be lucky to find a service tech who will touch a heat exchanger with a leak. Sure, it's plausible that leaks can be sealed with an appropriate heat-proof sealant (there are high temperature silicones).
The risks that I can think of include:
- not being able to see, find, access all of the leaks to seal them safely
- improper surface cleaning, bad bond, a "sealed" leak remains leaky
- since leaks due to rust are in the form of perforations that are usually surrounded by a larger thin-rusted area of steel, there is a real risk that just touching the leak area may poke a bigger hole, making repair difficult, or that the extent of sealant doesn't cover enough area and the patch is not reliable.
Watch out: Even though your heating unit is on a rooftop (thus outdoors) a heat exchanger leak can still send dangerous flue gases, even fatal carbon monoxide into building air.
So while no one is likely to be dumb enough to bet your life on any kind of promise or guarantee, you can yourself reduce risk by making darn sure that you've got working CO detectors properly installed in proper locations in the building.
See CARBON MONOXIDE - CO and CARBON MONOXIDE WARNINGS: HOME HEATERS
Question: safe silicone sealant for heat exchanger on a furnace?
(Nov 10, 2014) Anonymous said:
i have a silicone holding my heat exchanger tubes on some has come off is there a safe silicone for the air stream inside the furnace
Reply:
Anon
Yes probably. I would check with the unit's manufacturer for what sealants they recommend, particularly as heat and other issues will vary among equipment and even location within the same appliance
(Nov 10, 2014) Anonymous said:
Called american standard furnace they gave me a local repair mans # he said go to the automotive store i want the factory type but that wont even go there
Reply:
I doubt that's what the American Standard furnace manufacturer had in mind. Call someone else.
Question:
(Nov 16, 2014) craig loeschke said:
there is water leaking where the secondary heat exchanger is. Would that mean my heat exchanger is bad or is there a pan that is leaking. the condensate trap is doing its job, water around the base of the secondary heat exchanger is located. hoses are clear not plugged.
Reply:
The water leak from condensate could indeed destroy a heat exchanger. A more expert inspection is needed to assure your system is safe.
Question: Safety of furnace heat exchanger test procedures
Susan said: what is a heat exchanger test? Won't a pressure test suggested by my landlord cause damage to y furnace?
Reply:
Susan a heat exchanger test is a check for potentially carbon monoxide leaks out of a furnace into building air. There are several test approaches including the use of a tracer gas that will not risk damaging the system. I'm not sure what pressure test your tech has in mind. Discuss the system safety and the test risks with the service manager. Let us know what you're told.
Question: Oil burner forced hot air odor problem
(Sept 22, 2015) Steve Schassler said:
Oil burner forced hot air odor problem. In this small 1/2 duplex home severe uncombusted air smell. Severe summer summer months when furnace off. Bad also when furnace is on. During summer closed off all supply and return registers (sealed each one tightly) and oil smell has all but disappeared.
We have a new furnace but during pre-closing inspection, inspector could see burner flames via supply plenum access port due to a corrosion problem allowing combustion gases directly into supply plenum.
Could this be that supply ductwork has been contaminated prior to corrosion problem being fixed? Afraid to allow family to live in this unit. Recommendations?
Reply: warning about dangerous heat exchanger leaks
Steve:
Watch out: there is a Primary life-safety issue: if your home inspector could see the burner flames through the supply air plenum then the furnace is unsafe, should not be used, and needs repair or more likely replacement. It's not just an odor problem there's a risk of setting the building afire or dosing occupants with combustion gases that can be themselves harmful or dangerous.
I can't imagine what "fix" was done to a hole in a heat exchanger. The proper repair is to replace the heat exchanger or replace the furnace. Patch jobs are likely to be un-warranted and unsafe and unreliable.
We need a more accurate diagnosis of what you're smelling - "uncombusted air" I don't know what that means.
Secondary issue: If you are smelling heating oil odors then there has been a spill or there is a leak. Those odors may be transported through the building even when the forced air system is off. Follow the oil tank from fill through tank through piping through burner to look for leak possibilities. A spill of heating oil itself in the ductwork would be odd unless some fool ran oil lines though the ducts.
See ODORS FROM HEATING SYSTEMS
and
Question: is it safe to use a furnace with a small crack in the heat exchanger
(Mar 14, 2016) Anonymous said:
can i operate my furnace if there is a small crack
Reply:
Anon:
What we MUST say for LIFE SAFETY: depending on the heat exchanger crack size, location, and other conditions such as the blower fan and duct properties, it is possible for a heat exchanger crack to kill the building occupants with fatal carbon monoxide. Also keep in mind that what's a "small crack" (at least in your view - where "small" is not defined), it can suddenly become large as heat exchanger temperatures fluctuate.
The fact is that not every small heat exchanger crack is fatally dangerous:
For example in some positions (as I said it depends on where the crack occurs), when the blower fan runs air is pushed into the heat exchanger rather than allowing dangerous flue gases out into the building's duct system. When that's the case the only time you can even measure CO at the heat exchanger is during that interval between when the burner has turned-on and before the blower fan starts.
Watch out: But as I warned, small cracks can become big fatal ones. And there may be other cracks, holes, or damage that you've not seen. So no one in their right mind would tell you , not on-site, and not by e-text, that your heating system is safe. It is not.
...
Continue reading at HEAT EXCHANGER LEAK TEST - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
Or see these
Recommended Articles
- BACKDRAFTING HEATING EQUIPMENT
- BLUE vs YELLOW COMBUSTION FLAMES
- CARBON MONOXIDE WARNINGS: HOME HEATERS
- CO DETECTION OPTIONS
- COMBUSTION GASES & PARTICLE HAZARDS
- COMBUSTION PRODUCTS & IAQ
- CONDENSING BOILERS/FURNACES
- CONDENSING GAS FURNACE INSPECTION & TESTS
- GAS APPLIANCE / HEATER DIRECT VENT CLEARANCES
- GAS DETECTION INSTRUMENTS
- HEAT EXCHANGER CORROSION
- HEAT EXCHANGER CLEANING
- HEAT EXCHANGER LEAK TEST
- HOW to INSPECT HEATING SYSTEMS
- TEMPSTAR HVAC MANUALS for the manual for the heating system discussed on this page
Suggested citation for this web page
CONDENSING GAS FURNACE INSPECTION & TESTS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- [0] Keith R Prach, Residential Furnace Heat Exchangers : History of Metal Failure and Behavior Inspection Techniques and Procedure [at Amazon.com], KRP Enterprises, 1993, ISBN-10: 0963742426
ISBN-13: 978-0963742421
You may also be able to purchase this book from its author: Keith Prach, K&P Enterprises, Inc., 1800 E. Lincoln Suite C-3, Fort Collins CO 80524 - [0a] Ellis Prach,Heat Exchanger Experts Residential Furnace Inspection Manual [at Amazon.com, may be out of print], Heat Exchanger Experts Residential Furnace Inspection Manual [at Amazon.com], Quoting: This full-color residential furnace inspection manual will broaden your understanding of how defects occur in furnace heat exchangers and will enable you to accurately assess the integrity of any furnace. You will be led through the steps to identify defects, according to the history of metal failure in a variety of commonly used residential furnaces, and taught the techniques required to conduct furnace heat exchanger evaluations. The Heat Exchanger Experts Manual will prove to be invaluable for seasoned technicians, novice technicians and everyone in between
- [2] "Heat Exchanger Testing, Who's Right?" Dan Friedman, The ASHI Technical Journal, Vol. 2 No. 1, July1991. DJ Friedman (editor of InspectAPedia.com) served as a professional home inspector and forensic investigator of building failures from, 1986 to 2010. He previously operated a heating and cooling service and repair company and a residential construction and renovation firm.
- [3] "Case History: LP Gas Leak - Using the TIF 8800," Dan Friedman, The ASHI Technical Journal, Vol. 2 No. 1, July1991
- [4] "Choosing and Using a Carbon Monoxide CO Monitor," Dan Friedman, The ASHI Technical Journal, Vol. 2 No. 1, July1991
- [5] American Gas Association, Fundamentals of Gas Combustion, 7th printing, September 1985. Prepared by American Gas Association Laboratories for American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209 and Gas Appliance Manufacturers Association, Inc., 1901 North Fort Myer Drive, Arlington, VA 22209.
- [6] National Fuel Gas Code, NFPA 54 1988 and ANSI Z223.1 1988, available from AGA at the address above, or from the National Fire Protection Association, Batterymarch Park, Quincy MA 02269
- [7]NFPA and AGA, National Fuel Gas Code Handbook, Z223.2, same source as above
- [8] "Residential Gas Furnace Heat Exchanger Testing", Douglas DeWerth, P.E. American Gas Association (AGA) Laboratories under SAM number 630-92 9/86. , Refrigeration Service Engineer’s Society’s Service Application Manual (SAM)" The manual outlines and explains the many test methods that are used and have been used to inspect and test heat exchangers. This manual also goes into detail about the test equipment used in the 3 step method that the AGA developed. RSES members can view the SAM minus the photographs and diagrams at http://www.rses.org. If you are not a member or want to purchase a complete copy call RSES (800)297-5660 for availability and cost.
- [9] Furnace Heat Exchanger Leak Test, American Gas Association .
- Step 1 Visual inspection.
- Step 2 Burner flame deviation test.
- Step 3 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 of the heat exchanger.
- Source: http://www.aga.org/NR/rdonlyres/A156C36A-9324-4978-91B4-E78DB63DAD7D/0/8612FURNHEATEXCHNGLEAKTEST.pdf
- [11] AGA mixed gas test method for heat exchangers: see http://www.aga.org/pdf/publicinfo/co...facts8612b.pdf also see the gas test kit available from http://www.testproductsintl.com/gas.html
- American Gas Association, Fundamentals of Gas Combustion, 7th printing, September 1985. Prepared by American Gas Association Laboratories for American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209 and Gas Appliance Manufacturers Association, Inc., 1901 North Fort Myer Drive, Arlington, VA 22209.
- National Fuel Gas Code, NFPA 54 1988 and ANSI Z223.1 1988, available from AGA at the address above, or from the National Fire Protection Association, Batterymarch Park, Quincy MA 02269
- NFPA and AGA, National Fuel Gas Code Handbook, Z223.2, same source as above.
- DJ Friedman (editor of InspectAPedia.com) served as a professional home inspector and forensic investigator of building failures from, 1986 to 2010. He previously operated a heating and cooling service and repair company and a residential construction and renovation firm.
- Bacharach Instruments, 301 Alpha Drive, Pittsburgh, PA 15238 412-782-3500.
- Gas Tech, Inc., 331 Fairchild Drive, Mountain View, CA 94043 415-967-6794.
- Lynn Products Company, 400 Boston St., Lynn MA 01905 617-593-2500 and 617-596-0430 FAX.
- National Draeger, Inc. 101 Technology Drive Pittsburgh, PA 15275 412-878-8383 412-787-2207 FAX
- R.W. Beckett Corporation, PO Box 1289, Elyria, OH 44036 216-327-1060
- Sensidyne Corp. 12345 Starkey Rd. Suite E, Largo, FL 33453 813/530-3602. Sensidyne does not sell retail. Their equipment is marketed by Industrial Products Company, 21 Cabot Boulevard, Langhorne, PA 19047 800-523-3944 or in PA 800-562-3305. This distributor also can supply GasTec colorimetric tubes used with the Sensidyne calibrated pump.
- TIF Instruments,Inc., 9101 NW 7th Avenue, Miami, FL 33150. Some ASHI Members operate inspection equipment companies and offer varieties of gas detection equipment:
- Professional Equipment, 143 Plainview Road, Woodbury, NY 11797 800-334-9291.
- The Specialty Tool Company, 145 D Grassy Plain St., Bethel, CT 06801 800-456-4605.
- Draeger equipment is marketed to home inspectors by Kirsopp Home Inspections Inc., Belleville, IL 618-397-3057.
- Dan Friedman is an ASHI Member in New York, NY Metro ASHI President, chairs the ASHI Technical Committee, and edits the ASHI Technical Journal. He has owned and operated a heating equipment service and repair company.
- Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
- National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
- "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- Heating, Ventilating, and Air Conditioning Volume we , Heating Fundamentals,
- The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
CONTINUE READING or RECOMMENDED ARTICLES.
- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.
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