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 Guide to Draft Hoods on Gas Fired Heating Equipment
InspectAPedia® - 
- Draft Hoods & Vents: Guide to Draft Hoods on Gas Fired Furnaces, Boilers & Water Heaters - Purpose, Inspection, Repair
- Troubleshooting heating system drafts, vents, and chimneys - combustion air and carbon monoxide production
- AUTOMATIC VENT DAMPERS - separate article
- BACKDRAFTING HEATING EQUIPMENT & CARBON MONOXIDE - CO - separate articles
- CHIMNEY DRAFT & PERFORMANCE - separate article
- COMBUSTION AIR DEFECTS - separate article
- COMBUSTION AIR for TIGHT buildings - separate article
- COMBUSTION GASES & PARTICLE HAZARDS & COMBUSTION PRODUCTS & IAQ - separate articles
- COMPLETE COMBUSTION, Stoichiometric - separate article
- DIRECT VENTS / SIDE WALL VENTS - separate article
- DRAFT HOODS - gas fired
- DRAFT MEASUREMENT, CHIMNEYS & FLUES - separate article
- DRAFT REGULATORS, DAMPERS, BOOSTERS - separate article
- DRAFT REGULATOR SOOT INSPECTION - separate article
- DRAFT INDUCER FANS - separate article
- Questions & answers aboutdraft hoods on gas fired boilers & furnaces: inspection, troubleshooting, repairs, hazards
- References
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Here we explain Draft Hoods & Vents, providing a Guide to Draft Hoods on Gas Fired Furnaces, Boilers, Water Heaters and explaining
the Purpose, Inspection, Repair of these key venting devices on gas fired appliances. Details about draft control for gas fired heating systems, including furnaces or boilers, are discussed right here at Furnace Draft Hood on gas fired equipment. (Details about draft control on oil fired heating systems are discussed at Draft Regulators barometric dampers on oil fired equipment.
The articles at this website describe the basic components of a home heating system,
how to find the rated heating capacity of an heating system by examining various data tags and components, how to recognize common heating system operating or safety defects, and how to save money on home heating costs.
We include product safety recall and other heating system hazards.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Guide to Draft Hoods on Gas Fired Furnaces, Boilers, Water Heaters - Purpose, Inspection, Repair
What is a Gas Appliance, Furnace, Water Heater, or Boiler Draft Hood
This photo of a York gas fired furnace displays a conventional draft hood opening - the large horizontal
opening space shown in the middle of the furnace.
The purpose of this opening is to permit additional air to flow into the flue vent connector (stack pipe)
and chimney when the gas burner is operating. This additional air flow avoids excessive draft at the
gas burner.
Too much draft at the gas burner could result in improper gas combustion.
(The gas burner will be below this opening and behind
the cover with the louvered openings. The louvers provide combustion air to the gas burner.) |
The draft hood or draft
regulating device we are discussing here is normally
used only on gas-fired heating equipment, not on oil-fired equipment. The equivalent draft control on oil fired heating systems is discussed at
Draft Regulators barometric dampers on oil fired equipment.
This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.
Common Defects in Gas Appliance Draft Hoods
Improper gas appliance draft hood location or size is dangerous
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Dome type gas appliance draft hood clearances:: Dome type draft hoods are commonly installed
on gas fired heating boilers.
For dome type draft hoods such as the
funnel-shaped device shown at the center of this photo (air enters at the under-side of the dome)
the manufacturer of the boiler specifies the required distance from the bottom edge of the
hood to the top surface of the boiler.
Usually this clearance required for gas fired appliance draft hoods is given in inches, embossed right
into the lower edge of the draft hood itself.
Look for the draft hood clearance specification and measure what is actually installed. If the draft hood is installed too
close to the boiler top, or too high, too far above the boiler top, it will not work properly
and the system may be unsafe. |
Modification or removal of a draft hood can be very dangerous, and also the presence of rust
or debris on top of the boiler below the draft hood may indicate a dangerous condition such as
a blocked chimney - risking dangerous combustion gas or carbon monoxide spilling in the building.
We describe a case history where this occurred at
DANGEROUS CHIMNEY CASE STUDY.
Rust or damage at the gas heater or water heater draft hood and what it means
These photos show an unusual accumulation of debris at a gas fired furnace draft hood opening.
Rust at this location at a furnace draft hood could indicate an unsafe condition. If the chimney draft is inadequate or
if the chimney is blocked, or if the heater has been damaged by flooding or other wet conditions,
you may observe rust and debris on and around the gas operated furnace, boiler, or water heater
draft hood. Further inspection by an expert is needed.
Signs of Trouble at a Gas Fired Water Heater Draft Hood
Stains or debris at a water heater draft hood:: The black stains around the draft hood on this water heater were an indication of something seriously wrong
with the installation.
Tracing the flue vent connector from the draft hood atop the water heater (shown in this
photo) to its connection at a chimney (not shown) we found that while the water heater was a gas fired
appliance it was sharing a flue with an oil fired heating boiler whose chimney was blocked.
Backpressure
at the chimney was sending the oil burner's exhaust back down the gas-fired water heater's flue and into
the building. |
Flue gas spillage at a water heater draft hood:: Our client is pointing to the draft hood on the gas fired water
heater in the home she was buying.
We could see two things: first, foam insulation on the hot water pipe was melting
and second, we suspected that there was excessive flue gas spillage from this appliance. This is an unsafe condition
that needs investigation and repair. |
Blockages at a water heater draft hood:: this photo of a draft hood on the gas fired water
heater in the home lets us see two concerns:
First, the gas fired water heater's draft hood was partly blocked with hair - so the
water heater may not be burning its fuel nor venting its combustion gases safely.
Second, the previous owner of the
home must have kept a very hairy and shed-prone dog in the basement where it's hair was so thick in the air that
the draft hood was blocked. If this home were going to be occupied by someone with dog allergies, extensive
cleaning would also be in order.
More photos and descriptions of gas water heater defects including draft hood issues can be seen at GAS FIRED WATER HEATERS
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- [1] "Instructions for Installing FIELD Type AF Barometric Draft Controls," Form No. 31 DC 30666, Field Corporation, Mendota, IL 61342, web search 04/02/2011, original source: http://www.fieldcontrols.com/pdfs/04592700.pdf, Field Controls, Kingston, North Carolina 28501, Tel: 919-522-3031
- [2] Tjernlund Draft Controls, A Series (single action for oil, solid fuel, and fan-assisted gas burners) and B Series (double action for gas heating appliances), web search 04/02/1011, original source: http://www.tjernlund.com/Tjernlund_8500490.pdf , Tjernlund Products, Inc., 1601 Ninth Street, White Bear Lake MN 55110-6794, Tel: 651-426-2993 or 800-255-4208 website: www.tjernlund.com Email: fanmail@tjfans.com
- 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.)
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. 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 & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers,
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson, Dunlop & Associates Ltd., Toronto, Ontario, 2010, $69.00 U.S., 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.
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