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Guide to Draft Hoods on Gas Fired Heating Equipment
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Here we discuss 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. This website answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect residential heating systems to inform home owners, buyers, and home inspectors of common heating system defects.

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.

Also see GAS PIPING, VALVES, CONTROLS for more details on how to inspect and test LP and natural gas piping, controls, valves, and tanks. We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2010 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.

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.

Common Defects in Gas Appliance Draft Hoods

Improper gas appliance draft hood location or size is dangerous

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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• Additional technical contributors & reference sources for this article are listed below.

Use links just below or 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.

CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEYS & Flues - Asbestos Transite Pipe
CARBON MONOXIDE/DIOXIDE
CARBON MONOXIDE WARNING
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEYS & Flues - Asbestos Transite Pipe
COOL OFF HEAT Thermostat Switch
COMBUSTION AIR
COMBUSTION AIR for TIGHT BUILDINGS
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
DEFINITION of Heating & Cooling Terms
DRAFT HOODS - gas fired
DRAFT REGULATORS - barometric dampers

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

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• ...

More Information on Building Diagnostic Inspections and Repairs

• Carbon Dioxide Gas Toxicity
• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• Dust from HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• 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
• Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• 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.)

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