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Checklist for heating equipment combustion air safety defects & hazards:
This procedure is only intended for buildings where LP gas or natural gas heating appliances (heating boiler, warm air furnace, water heater) are installed AND where a flue gas spillage safety switch such as a Tjernlund UC1 Universal Control, MAC1E or MAC4E auxiliary controls for gas fired equipment or Field Controls Gas Spillage Sensing Kit Model GSK-3, GSK-4, GSK-250M switches are installed on those appliances.
This article series explains how to recognize and fix combustion air defects on heating appliances such as boilers, furnaces, and water heaters. These articles answer most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. Our photo at page top shows an oil fired furnace installed in a closet with an airtight door; there was no outside combustion air supply. The heating system could not work properly nor safely in this home.
Guide to a Simple Combustion Air Safety Check for Gas Fired Heating Appliances
Thanks to Tjernlund Products who recommended this procedure, we describe a simple combustion air safety check that can be performed by a homeowner or by a heating service technician.
Watch out: inadequate combustion air not only causes improper and wasteful operation of heating equipment it can also produce fatal carbon monoxide gas hazards indoors. The quantity of combustion air needed depends on the fuel type, the input BTUh rating of the heating equipment, and additional air needed to assure effective exhaust draft to carry combustion products safely out of the building.
This procedure is only intended for buildings where LP gas or natural gas heating appliances (heating boiler, warm air furnace, water heater) are installed AND where a flue gas spillage safety switch such as a Tjernlund UC1 Universal Control, MAC1E or MAC4E auxiliary controls for gas fired equipment or Field Controls Gas Spillage Sensing Kit Model GSK-3, GSK-4, GSK-250M switches are installed on those appliances. (Similar products are provided by other manufacturers.)
Close all doors and windows of the building. If the gas fired heating appliance is installed in a utility room or closet, close the entry door to that room. Close all fireplace dampers. Turn on the clothes dryer (if installed) and all exhaust fans such as range hoods, bathroom exhaust vent fans, whole house fans, and radon mitigation fans, running all fans at their maximum speed.
Turn on and place in operation the gas fired heating appliance on which the flue gas spillage sensor switch to be tested has been installed. Set the appliance thermostat for continuous operation. If other gas fired appliances are installed in the same building run those appliances at the same time.
Allow the fans turned on in step 1 to operate for fifteen minutes.
If the flue gas sensor spill switch trips during the fifteen minute test period this means that an unsafe condition exists. Check all of the appliances for a venting malfunction and check for adequate combustion air. (The occurrence of the flue gas spillage safety switch tripping may indicate inadequate combustion air but it could also indicate an unsafe chimney or some other unsafe condition.)
Also see CHIMNEY INSPECTION DIAGNOSIS REPAIR.
TURN OFF FUEL SUPPLY to the gas fired appliance that caused the safety switch to trip.
DO NOT OPERATE THE GAS APPLIANCES UNTIL THE UNSAFE VENTING CONDITION HAS BEEN INVESTIGATED BY A PROFESSIONAL CONTRACTOR or GAS UTILITY COMPANY SERVICE PERSONNEL.
See CARBON MONOXIDE WARNING.
Return all windows, doors, fans, to their previous conditions of use.
SAFETY WARNING: If AT ANY TIME your gas fired equipment has shut down in SAFETY OFF position it may be due to a resettable flue gas spill sensor switch. Check with your heating service company - you might think you can avoid a costly heating service call, BUT BEWARE: because flue gas spillage is very dangerous, including the production of potentially fatal carbon monoxide gas, don't simply reset the system without finding out what caused the problem in the first place.
MORE SAFETY WARNINGS: in addition to our safety warning above, Tjernlund explains that flue gas safety switches are intended to alert the building occupants to a potentially dangerous condition.
But flue gas spillage safety switches are not a substitute for a regular chimney safety inspection nor do they replace regular heating appliance inspection and maintenance by a trained technician. Those steps must be taken as well.
What causes flue gas spillage:
Please see SPILL SWITCH, FLUE GAS DETECTOR for a discussion of the causes of flue gas spillage in buildings and for a description that contrasts inadequate combustion air with other causes of dangerous flue gas leakage into buildings.
Bachrach Corporation, a manufacturer of heating system test equipment opines that gas fired equipment is more likely to have flue gas spillage from a blocked chimney than from building depressurization due to inadequate combustion air supply. We're not sure what data supports that view.
Certainly home inspectors find many heating appliances installed in tiny closets with no outside combustion air and a door that, when shut, blocks off air to the appliance. We have also observed that gas fired heating equipment operated just fine in a building until a new owner installed a whole house ventilation fan system.
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Questions & answers or comments about combustion air requirements and safety hazards for oil and gas fired heating appliances
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American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook - Fundamentals, 1993, Chapter 15, page 15.9 Air For Combustion.
ASME CSD-1- Controls and Safety Devices for Automatically Fired Boilers, 1992 with addendum 1a 1993. section CG-260 Combustion Air.
BOCA - National Mechanical Code, 1990, article 10, Combustion Air.
NFPA 31 - Installation of Oil Burning Equipment, 1992, section 1-5 Air for Combustion and Ventilation.
NFPA 54: National Fuel Gas Code (2015), addresses heating appliance combstion air ventilation specifications. NFPA 54, ANSI Z223.1 provides minimum safety requirements for the design and installation of fuel gas piping systems in homes and other buildings.
NFPA 85: Boiler and Combustion Systems Hazards Code: NFPA 85 contributes to operating safety and prevents explosions and implosions in boilers with greater than 12.5 MMBTUH, pulverized fuel systems, and heat recovery steam generators.
NFPA 87: Recommended Practice for Fluid Heaters, This recommended practice provides safety guidance for fluid heaters and related equipment to minimize fire and explosion hazards that can endanger the fluid heater, the building, or personnel
SBCCI- Standard Mechanical Code, 1991, section 305 Combustion and Ventilation Air.
Axtman, William H., "Combustion Air Requirements: The Forgotten Element in Boiler Rooms", Grayh Gull Associates, retired executive director of the American Boiler Manufacturers Association, National Board Technical Series, Winter 1995 National Board Bulletin. Retrieved 26 January 2015, original source: http://www.nationalboard.org/index.aspx?pageID=164&ID=191
Excerpt: Several safety codes such as the National Fire Protection Association's standards, NFPA 54 - National Fuel Gas code, NFPA 31 - Installation of Oil Burning Equipment, and the American Society of Mechanical Engineers (ASME) CSD-l Controls and Safety Devices for Automatically Fired Boilers have sections covering the requirements for combustion air intakes. In addition, building codes such as the Building Officials and Code Administrators International (BOCA) National Mechanical Code and the Standard Mechanical Code published by the Southern Building Code Congress International (SBCCI) have air requirements for combustion. Editor's note: Some ASME Boiler and Pressure Vessel Code requirements may have changed because of advances in material technology and/or actual experience. The reader is cautioned to refer to the latest edition and addenda of the ASME Boiler and Pressure Vessel Code for current requirements.
Nussbaumer, Thomas. "Combustion and co-combustion of biomass: fundamentals, technologies, and primary measures for emission reduction." Energy & fuels 17, no. 6 (2003): 1510-1521.
Utiskul, Yunyong P., Wu, Neil P., Biteau, Hubert, "Combstion Air Requirements for Power Burner Appliances, Final Report", The Fire Protection Research Foundation, The Fire Protection Research Foundation
One Batterymarch Park
Quincy, MA, USA 02169-7471
http://www.nfpa.org/foundation, retrieved 25 Jan 2015, original source: http://www.nfpa.org/~/media/files/research/research%20foundation/rfcombustionairrequirements.ashx, Executive Summary: Gas-fired appliances require combustion air to properly function. Adequate air is necessary for
supporting combustion of the appliance burner, dilution of flue gas, and proper ventilation of the
space where the appliance is installed. Current standards and model codes outline requirements
and methods to supply the combustion air. One method is to provide outdoor combustion air
through openings or air ducts communicating with the outdoors through natural ventilation.
Most standards require the outdoor opening(s) be prescriptively sized based on the total energy
input rating of the appliance. However, in the United States, the current standards contain no
separate provisions to address the opening size supplying the combustion air for
commercial/industrial sized appliances, which typically have a high energy input rating of
greater than 300 kBtu/hr and are equipped with a power burner unit. As a result, the opening(s)
can be excessively sized when determined based on the current standards.
This research project establishes minimum outdoor combustion air requirements specific to gasfired
appliances utilizing power burners with input ratings no greater than 12.5 MBtu/hr. A
review of the available literature, engineering guidelines, and current standards and model codes
related to combustion air requirements was performed. This report provides an understanding
of the technical basis for the existing provisions for combustion air and their applicability to
power burner appliances. This report also identifies the range of energy input ratings for gasfired
appliances equipped with power burners, and compares the combustion air requirements
specified by a range of appliance manufacturers. A theoretical model for air flow through
openings was developed and the modeling results, together with the data gathered through the
literature review, were used to provide a baseline to establish the theorized combustion air
requirements suitable for power burner appliances.
 Jeff Wilcox, "Evaluating Duct Work, How to Evaluate Furnace Duct Work & Cure Short Cycling or Inadequate Ductwork Problems" Vermont Department for Children and Families, Office of Economic Opportunity, - dcf.vermont.gov/sites/dcf/files/pdf/oeo/WAPManual/AppendixI.pdf retrieved 12/5/2013. Geoff Wilcox
Vermont Office of Economic Opportunity
Weatherization Assistance Program
Reference Material for the original article came from:
1. Saturn Mechanical Systems Field Guide
2. Bacharach (Rudy Leatherman)
Field Controls provides instructions for the installation of LP and Natural Gas spill sensor switches, for example for their Gas Spillage Sensing Kit Model GSK-3, GSK-4, GSK-250M switches. Contact your heating service technician directly, or contact Field controls at fieldcontrols.com for more information. These switch models include a manual reset switch. Field Controls, Kingston NC 28504 - Tel 252-522-3031.
Tjernlund Products provides instructions for the installation and use of their controls, including the WHKE Millivolt Interlock Kit for use with their UC1 Universal Control, MAC1E or MAC4E auxiliary controls for gas fired equipment. This document also describes Tjernlund's recommended combustion air safety check which we recommended in this article. Contact Tjernlund Products at tjernlund.com or at 800-255-4208.
Bachrach Corporation, www.bachrach-training.com provides education for HVAC technicians. We found their web pages hanging during loading -01/2009. Readers may want to contact the company directly at: bacharach-inc.com or at 800-736-4666.
R.E. Prescott Company, a producer of other REPCO™ residential and industrial products as well as a provider of design-build engineering services is at 10 Railroad Avenue, Exeter, NH 03833. Tel: 603-722-04321 or 888-786-7482. Trish O'Keefe from Prescott informed us (10/7/2009) that their company had nothing to do with the failed Repco heating boilers discussed at InspectAPedia.com. She wrote:
Our company manufactures & distributes residential water treatment equipment, including our Repco line of conditioners. We have a plumbing & heating supply dept as well. We are mistaken for the Repco Boiler company on a regular basis, most frequently in Oct. and Nov.
Any information you could give me on the other Repco company would be appreciated. We've assumed it is no longer in business, and we'd like to know that for sure. Many callers want to know where to get replacement parts and I would be glad to direct them if I knew...plus there's always a chance they might be interested in a Crown Boiler instead
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & 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 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.)
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.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 extensive home inspection education and report writing material.
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.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume.
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