Guide to Draft Hoods on Gas Fired Heating Equipment
DRAFT HOOD, GAS HEATER - CONTENTS: 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
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Draft regulation for gas fired heating equipment: draft hoods.
Here we explain the purpose and function of draft hoods or vents on gas fired boilers, furnaces, water heaters or other gas fired heating equipment. This article explains the purpose of these key venting devices on gas fired appliances.
We list and give photo-examples of common operating and safety defects found at draft hoods and draft regulators on gas fired heating equipment.
Guide to Draft Hoods on Gas Fired Furnaces, Boilers, Water Heaters - Purpose, Inspection, Repair
This article describes draft regulation on gas fired heating equipment.
[Click to enlarge any image]
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. If your heater is oil-fired or you are using a wood or coal stove, see DRAFT REGULATOR, DAMPER, BOOSTER for draft regulation and barometric dampers on oil fired heating equipment.
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
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.)
Defects & Trouble Signs 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.
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.
Soot at the Draft Hood or Elsewhere on Gas Fired Heating Equipment
Watch out: the presence of fragments of soot or soot staining on gas fired heating equipment may indicate a very dangerous condition in which improper combustion, probably inadequate combustion air or a blocked chimey or flue, can cause the production of fatal carbon monoxide gas in the building.
The safest step if you see soot formation at gas fired heating equipment is to turn it off immediately.
In all events be sure that you have working carbon monoxide detectors properly installed and located in the building as well, of course, as smoke detectors and alarms.
Watch out: 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.
at the chimney was sending the oil burner's exhaust back down the gas-fired water heater's flue and into
Unsafe 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.
Watch out: This is an unsafe condition
that needs investigation and repair.
Dangerous Blockages at a water heater draft hood
Watch out: Look for signs of debris or any other material that blocks clear flow of air into the gas heater's draft hood. Blockage can cause improper venting, improper combustion, and even an increase in heating costs.
This photo (at left) 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.
This article series 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.
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.
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 "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
 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: email@example.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 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: firstname.lastname@example.org
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