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Explanation of Chimney Wet Time & Metal Chimney Corrosion InspectAPedia®  -     Here we provide an Explanation of Chimney Wet Time & Metal Chimney Corrosion Chimney inspection advice includes detailed attention to rust, pitting, corrosion on metal chimneys

This article describes the hidden safety hazards caused by rust and corrosion of metal chimneys and flues.

This website provides detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed. As with most inspection and safety topics, this material may be incomplete.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Wet time and Corrosion in Chimneys and Vents

Recommended venting systems with draft hood appliances were developed in the 50's for atmospheric aspirated appliances. The efficiencies were low and approximately 35% of the energy input was wasted.

Newer mid-efficiency Category I appliances have a much lower flue gas temperature and reduced off-cycle losses.

These new furnace designs alter the vent gas temperature, dew point temperature, flow rate and dilution air in the vent.

The result is that in modern metal chimneys, regardless of the metal used or other chimney construction details, there is much greater potential for condensation and corrosion.

Factors that control the degree and duration of wet conditions in metal chimneys and vent systems are critical to the life of the appliance.

The Gas Research Institute Venting Project reported (and subsequently published in the 1996 National Fuel Gas Code) the following venting occurrences:

1. The reduced dilution air increases the chances of more condensate to form in the vent.
2. Reduced flue gas temperatures result in oversized vents not heating quickly which contribute to increased condensation.
3. Reduced dilution air increases the maximum capacity of a vent.

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STRUCTURAL INSPECTIONS & DEFECTS
CARBON MONOXIDE
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEY INSPECTION & REPAIR GUIDE
Chimney Components Definitions
Abandoned Chimneys
Backdrafting Appliances
Chimneys Cleaning Advice, Procedures
Chimney Cleanout Doors
Chimney Crack & Collapse Risks, Repairs
Chimney Crack Detection & Diagnosis
Chimney Draft & Performance
Chimney Leaning, Separation, Movement
Chimney Height & Clearance
Chimney Inspection Checklist
Most Frequent Chimney Defects
Chimney Inspection Checklist - Outdoors
Chimney Inspection Checklist - Indoors
Responsibility of an ASHI Home Inspectors
Chimney Inspection: Flue Interiors
Flue Interior Inspection Methods
Chimney Inspection Indoor Procedures
Abandoned Chimneys - Indoor Inspection
Abandoned Chimneys: Outdoors
Angled Chimney Flues
Attic Chimney Inspection
Blocked Chimney Flues
Bracket Chimney Collapse & Fire Risks
Chimney Crack Detection & Diagnosis
Dead End Chimney Flue Hazards
Fire Clearance Safety Hazards
Fire stopping at Chimney Passage Through Floors
Transite Pipe Chimneys & Flues
Unlined Flue Inspections
Chimney Inspection Outdoors From Ground
Chimney Inspection Outdoors at Rooftop
Angled Chimney Flues
Blocked Chimney Flues
Chimney Cap & Crown Inspection
Chimney Crack Detection & Diagnosis
Chimney Exterior Spalling
Chimney Flashing Mistakes & Leaks
Chimney Height Extensions
Chimney Shoulder Leaks
Flue Tile Damage in Chimneys
Masonry Chimney Top Damage
Soot at the Chimney Top
UNLINED FLUE INSPECTIONS
Chimney Repair Methods
Chimney Safety - CPSC Alert
Chimney Spalling
Chimney Types & Materials
CO2 TOXICITY
COALSTOVE SAFETY
COMBUSTION PRODUCTS & IAQ
Dead End Chimney Flue Hazards
Definitions of Chimney Types & Parts
DRAFT HOODS - gas fired
DRAFT REGULATORS, DAMPERS, BOOSTERS
Fire Clearances for Masonry Chimneys
Fire Clearances for Metal Chimneys
Fire Clearances, Single-Wall Metal Flues
Fireplace Damage & Unsafe Hearths - Settlement
Flue Sizing of Chimneys
Flue Vent Connectors - Boilers, Furnaces
Fuel Changes for Heating Appliances
HEATING INSPECTIONS
HOME HEATING SAFETY
Metal Chimneys & Flues
  Bracing for Metal Chimneys
  Class A Chimneys, MetalBestos™
  Connecting Metal Chimney Sections
  Continuous metal chimneys
  Definitions of Chimney Types & Parts
  Fire Clearances for Metal Chimneys
  Height required for L Vents & B Vents
  Indoor Hazards, Metal Chimney & Vent
  Manufactured Chimneys
  Offset from Vertical in Chimneys, excessive
  Replacement Components for Metal Chimneys
  Single-Wall Metal Vents & Chimneys
  Super Chimneys, 629 Chimneys
  Triple-Wall Metal Fireplace Chimneys
  Type B-Vents
  Type L Vents
  Wet time & Corrosion in Chimneys, Vents
  Wood Framed Chimney Chases
Moisture Problems Damage Chimneys
OIL HEAT SAFETY INSPECTIONS
PLASTIC HEATER VENTS
PLASTIC VENTS Goodman HTPV RECALL
Shared Chimney & Shared Flue Hazards
Stains on chimneys
Transite Pipe Chimneys & Flues
UNLINED FLUE INSPECTIONS
Wood Burning Heaters Fireplaces Stoves
Coalstove Safety
Dead End Flues - Dead Base Chimney Hazards
Fire Clearance Safety Hazards
Fire stopping at Chimney Passage Through Floors
HEATING COST FUEL & BTU Cost Table
Woodstove Safety

• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
• Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at ap@octoberhome.com
• Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
• Gas Research Institute Venting Project is cited at www.energyd.com/gas_vent.htm and its results are reflected in the National Fuel Gas Code cited just below.
• Chimney Building Codes and Chimney, Flue, and Appliance Venting Standards
  • NFPA #211-3.1 1988 - Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
  • NFPA # 54-7.1 1992 - Specific to venting of equipment with fan-assisted combustion systems.
  • GAMA - Gas Appliance Manufacturers' Association has prepared venting tables for Category I draft hood equipped central furnaces as well as fan-assisted combustion system central furnaces.
  • National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
  • Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
  • Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys, refers to Chapters 23, 29, and 37 of the Building Code.
  • New York 1984 Uniform Fire Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
  • New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a flue liner was listed in the One and Two Family Dwelling Code for New York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979 Building and Fire Prevention Code:
• "Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
• Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
• "Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
• "Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
• "Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection.htm. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
• Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
• US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html

Books & Articles on Chimney Inspection, Testing, Diagnosis, & Repair

• Books, Complete List of Fireplace & Chimney Design, Inspection, Repair Books at the InspectAPedia Bookstore.
• Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
  The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
  Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Available at the InspectAPedia Bookstore.
• Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
• Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
• Fireplaces, a Practical Design Guide, Jane Gitlin
• Fireplaces, Friend or Foe, Robert D. Mayo
• NFPA 211 - Standards for Chimneys & Fireplaces, NFPA
• Principles of Home Inspection: Chimneys & Wood Heating (Principles of Home Inspection), Carson Dunlop
• Woodstove & Fireplace Maintenance & Safety, L. L. Helwig

More Information on Building Diagnostic Inspections and Repairs

• NFPA 211 - 3-1.10 - Relining guide for chimneys
• NFPA 211 - 3-2 - Construction of Masonry Chimneys
• NFPA 211 - 3-3 - Termination Height for chimneys
• NFPA 211 - 3-4 - Clearance from Combustible Material
• NFPA 54 - 7-1 - Venting of Equipment into chimneys
• Brick Institute of America - Flashing Chimneys
  Brick Institute of America - Proper Chimney Crowns
  Brick Institute of America - Moisture Resistance of Brick
• American Gas Association - New Vent Sizing Tables
• Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
• National Chimney Sweep Guild - Yellow Pages of Suppliers

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