Heat Exchanger & Chimney Flue Damage From Heating Equipment Condensation
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Review of damage to high efficiency heating boilers and furnaces (condensing boilers or condensing furnaces) due to condensation and corrosion
Can older furnaces or boilers also cause condensation damage when duty-cyclers are installed?
Problems Connecting a Higher Efficiency Furnace or Boiler to an Old Chimney and Flue
Effect of Duty Cyclers on Heating System Efficiency & Performance
Questions & answers about handling condensate from high efficiency boilers or furnaces
Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

This article discusses damage to high efficiency heating equipment caused by condensation and corrosion to heat exchangers or flues, and we address the question of condensation and corrosion damage with older heating equipment that uses duty cycle controls.

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Causes of Condensation & Corrosion Damage at High Efficiency Condensing Boilers & Furnaces; Condensation Damage with Older Heating Equipment?

Sketch at page top is courtesy of Carson Dunlop Associates. The accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. See CONDENSING BOILERS/FURNACES, and be sure to review Safety Recalls, Chimneys, Vents, Heaters. Also, readers should also see our extensive list of heating system inspection, diagnosis, maintenance and repair articles at HEATING SYSTEMS.

The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Topic: High Efficiency & Conventional Heating Furnace or Boiler Damage from Condensation

Question: Did the change to stainless steel heat exchangers fix the condensation damage worry with high efficiency heating furnaces and boilers? What about older heating equipment that uses a duty cycle timer?

A heating salesman mentioned that lawsuits were pending (in 1985) against some manufacturers of high-efficiency furnaces (and boilers) - that although condensation problems had been solved through the use of stainless-steel heat exchangers, there were new problems arising from the lower-temperature flue gases.

Also, are there any documented cases of condensation damage in older furnaces (or boilers) stemming from the use of duty-cyclers lowering flue gas temperature? - Jeff A. Pendl, Enervision, Cincinnati OH

Answer: Higher Efficiency Heating Systems are Designed to Handle Corrosive Condensate

Higher-efficiency heating boilers and furnaces (HIGH EFFICIENCY BOILERS/FURNACES) have cooler exhaust gases, which may condense in different parts of the system. If the entire system, including the heating unit itself and its venting components were not designed to handle the corrosive condensate, problems may occur.

The very high-efficiency condensing furnaces and boilers are designed to condense liquid in the heat exchanger. While some early models had troubles (see Safety Recalls, Chimneys, Vents, Heaters), we are not aware of any current problems or lawsuits.

Condensing furnaces (warm air heat) or condensing boilers (hot water heat) use stainless-steel heat exchangers, plastic flue vent piping, and other system components that resist corrosion.

Watch out: if plastic vent piping for high efficiency heating equipment is not properly installed so that condensate is drained to a proper location, the system may become blocked or unsafe, as is happening in our photo, above left.

Problems Connecting a Higher Efficiency Furnace or Boiler to an Old Chimney and Flue

You are more likely to run into trouble when fitting a new, more efficient furnace or boiler to an old flue [especially with gas-fired heating equipment], or when retrofitting devices that lower flue gas temperatures.

In particular, problems are likely when the draft is already marginal due to a cold exterior chimney, extra long flue-vent-connector piping between the heater and the chimney, or other flue problems such as inadequate combustion air and very tight house construction.

See COMBUSTION AIR for TIGHT buildings and also the more technical problem discussion at Wet time & Corrosion in Chimneys, Vents. Also see Moisture / Frost Damaged Chimney.

Watch out: inadequate draft, backdrafting, and inadequate combustion air significantly increase the risk of production of dangerous, possibly fatal carbon monoxide gas. Be sure that your home is protected by working, properly-installed, properly located smoke detectors and CO detectors. (For more information see CARBON MONOXIDE - CO)

Effect of Duty Cyclers on Heating System Efficiency & Performance

As for the particular device you mentioned, a duty cycler, researchers at the America Gas Association Laboratory (AGA) suggest that they are unlikely to cause condensation problems.

[In at least part, that's because a properly designed and installed duty cycler must assure that the heating equipment runs long enough to reach proper operating temperature and thus also to vent properly.- Ed.]

Photo of automatic flue vent damper (C) Daniel Friedman

Nor are duty cyclers likely to boost the efficiency of the heating system more than 1 or 2 percent.

Other energy savers such as heat reclaimers and automatic flue vent dampers (see Automatic Vent Dampers) like the one shown at left are more effective.

But stick with certified devices, follow the installation specifications, and consult with the manufacturer to be sure you have and are following the installation manual for the device.

Details about how to reduce heating costs are found at HEATING COST SAVINGS METHODS.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Original article

The link to the original Q&A article in PDF form immediately below was preceded (above) by an expanded/updated online version of this article.

Q&A on Heat Exchanger & Flue Damage from Condensation in Heating Boilers or Furnaces - PDF version, use your browser's back button to return to this page. Original article, Solar Age Magazine, September 1985, adapted and updated for InspectAPedia.com November 2010.

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CONDENSING BOILERS/FURNACES
CONDENSING BOILERS/FURNACES DAMAGE

Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in buildings, and other topics.
Carrier Model BW9 Gas-Fired Condensing Boiler - Gas Fired Direct Vent Condensing Boiler - Example Installation & Operating Manual
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
HEATING SYSTEMS (see master list of heating articles at page left)
Lennox Furnace Manuals

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
DUST CONTAMINATION FROM HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
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.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"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 I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
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.)
Links to our list of additional information on heating system inspection, repair, maintenance
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Causes of Condensation & Corrosion Damage at High Efficiency Condensing Boilers & Furnaces; Condensation Damage with Older Heating Equipment?

Topic: High Efficiency & Conventional Heating Furnace or Boiler Damage from Condensation

Answer: Higher Efficiency Heating Systems are Designed to Handle Corrosive Condensate

Problems Connecting a Higher Efficiency Furnace or Boiler to an Old Chimney and Flue

Effect of Duty Cyclers on Heating System Efficiency & Performance

Original article

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair