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Reducing Risk for Fuel-Fired Equipment and Fuel Oil Storage

Installing, inspecting and maintaining heating equipment and fuel storage tanks correctly reduces fire risk and enhances safety.

Industrial Boilers

November 2, 2021

By John Taecker, senior regulator engineer, Distinguished Member of Technical Staff, and Kelly Nicolello, senior regulator engineer

Safer operation of fuel-fired appliances and equipment requires proper installation and periodic inspection, testing and maintenance as mandated by the model codes and equipment standards.  Compliance with the manufacturer’s instructions is also essential for safe installation and operation and is often explicitly called out in the equipment listing and the model codes.

For the purposes of this article, the term “appliance” refers to any device or apparatus used for heating. The term “equipment” refers to related piping, ducts, vents, control devices, and other systems components other than the appliances.

Depending on the type of fuel, safety installation requirements are included in different International Association of Plumbing and Mechanical Officials (IAPMO), International Code Council (ICC) and National Fire Protection Association (NFPA) model codes and standards. Section 605 of the 2021 International Fire Code (IFC) and Chapter 11 of NFPA 1 Fire Code include additional requirements for the continued use of installed equipment and the use of portable equipment.

Summary table of applicable installation codes and standards:

Fuel Source




LP gas




Natural gas








Solid fuel, e.g., wood or charcoal



NFPA 211

IAPMO = International Association of Plumbing and Mechanical Officials
UMC = Uniform Mechanical Code
UPC = Uniform Plumbing Code
ICC = International Code Council
IBC = International Building Code
IFGC = International Fuel Gas Code
IMC = International Mechanical Code
IRC = International Residential Code
NFPA = National Fire Protection Association
NFPA 31, Standard for the Installation of Oil-Burning Equipment
NFPA 54, National Fuel Gas Code
NFPA 58, Liquefied Petroleum Gas Code
NFPA 211, Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances

Any associated electrical wiring and equipment used in connection with fuel-fired equipment is to be installed and maintained according to NFPA 70, the National Electrical Code.

Type of fuel source

You should only use fuel-fired appliances and equipment with the fuel for which the appliance or equipment has been certified. For example, a gas-fired appliance intended to be fueled by natural gas cannot be fueled by LP-gas. Some equipment will have specific instructions to convert the gas-fired appliance for use with another type of gas. These instructions are part of the listing of the product.

UL 296, Oil Burners, requires the oil burner manufacturer’s instructions to identify the required grade of fuel oil that can be safely used in the appliance.  These appliances cannot use oil containing gasoline. Waste crankcase oil is an acceptable fuel in Group F, M and S occupancies for equipment listed and labeled for use with waste oil.  While not specifically referenced in the model fire codes, the standard for this equipment is UL 296A, Waste Oil-Burning Air-Heating Appliances.

Installation, use and maintenance of nonportable appliances and equipment

Installation codes and standards require nonportable appliances and equipment to be installed, used and maintained per their listing and the manufacturer’s installation instructions. The product evaluation includes a review of these instructions. 

The installation codes and standards for nonportable appliances include requirements for minimum combustion air, minimum clearances to combustible materials and working clearances and access to the apparatus. 

Proper venting of smoke and hot gases from fuel-fired appliances and equipment to outer air is critical.

Masonry chimneys need to be properly lined and not have open mortar joints. UL 1777, Chimney Liners outlines the requirements for chimney liners. To ensure metal chimneys are not corroded or improperly supported, they need to be inspected routinely to avoid separation at the joints or seams. 

Factory-built chimneys and vents are systems that need to utilize the connectors and end caps that are part of the listing of that system. The mechanical and fuel-gas codes provide the requirements for the proper selection of a chimney or vent system for each specific appliance, based on factors including the type of fuel source and the temperatures of the flue gases. Any decorative shroud used at the exterior termination of these systems must be listed and labeled for use with that system. Factory-built chimneys that are listed and labeled to UL 103, Factory-Built Chimney for Residential Type and Building Heating Appliances, are commonly paired with solid-fuel type room heaters that are listed and labeled to UL 1482.

For solid fuel-fired equipment, any fireplace accessories used in a masonry fireplace must be listed and labeled according to UL 907, Fireplace Accessories, and installed according to the manufacturer’s instructions and NFPA 211. Fireplace accessories include components, such as heat exchangers, combustion air vents, glass door assemblies, fire chamber panels and forms, smoke chamber surfacing materials, direct-connect systems, termination caps and similar equipment.

The addition of any accessories to a factory-built fireplace, such as unvented gas log heaters, fireplace inserts or gasketed fireplace doors, is not permitted unless the factory-built fireplace was specifically tested, listed and labeled for such use in accordance with UL 127, Factory-Built Fireplaces. Factory-built fireplaces are designed for installation with specific clearances to combustible materials. The addition of accessories not tested with that fireplace may increase the temperatures on the outside surface of the fireplace beyond allowable safe limits.

Use and maintenance of portable fuel-fired appliances

Provisions for the use and maintenance of portable fuel-fired appliances are covered in the model fire codes. These appliances must be used, stored and maintained per their listing and the manufacturer’s instructions. Product evaluations for listing include a review of these instructions.

The model fire codes allow portable unvented kerosene heaters listed to UL 647, Unvented Kerosene-Fired Room Heaters and Portable Heaters, to be used within one and two-family dwellings under specific conditions. According to the listings, these heaters cannot be used in sleeping rooms, bathrooms or storage closets; may be placed on combustible floors and used with clearances to combustible materials not less than 36 inches. Users must be cautious to avoid overturning them or allowing them to come into contact with furniture, curtains, draperies, etc. The design of this type of kerosene heater helps prevent the overflow of oil if the flame has been extinguished. 

These heaters include a mark to identify the fuel allowed for use, such as No. 1-K, STM D3699 kerosene fuel or certified synthetic fuels for certified kerosene-fired portable heaters and room heaters. Using certified synthetic fuels for certified kerosene-fired portable heaters and room heaters delivers an average fuel consumption rate equal to or less than the marked rating on a product's rating plate.

Fire codes define limitations on the storage and use of portable outdoor gas-fired heating appliances. The codes specify minimum clearances to buildings, minimum clearances to combustible materials and proximity to exits.  

Patio heaters are listed and labeled to ANSI Z83.26/CSA 2.37, Gas-Fired Outdoor Infrared Patio Heaters. Marks on these heaters note minimum clearances and appropriate types of surfaces for use. The installation instructions will indicate if an appliance is suitable for overhead suspension, overhead angle mounting, wall mounting, floor, mounting or table-top use.  Although the model fire codes include safety requirements for tip-over switches and guards to prevent accidental contact, these features are already required by the standard used to certify these products.

Portable outdoor gas cooking appliances, such as barbecues and grills, are listed and labeled according to ANSI Z21.58/CSA 1.6, Outdoor Cooking Gas Appliances. Marks on these appliances note minimum clearances and types of surfaces for safe use.  These appliances are only to be used outdoors, and are only intended for cooking purposes.  Devices intended for connection to a self-contained LP-gas supply system with an integral cylinder mounting accommodate a single, vertically mounted cylinder with a maximum size of:

  • 20 lb (9.1 kg) of fuel for outdoor cooking gas appliances with input ratings less than 80,000 Btu/h
  • 30 lb (13.6 kg) of fuel for outdoor cooking gas appliances with input ratings greater than or equal to 80,000 Btu/h

Fuel oil storage systems

The model fire codes establish what types of tanks and fuel-oil piping systems are permitted outside aboveground, inside buildings and underground. They also establish the maximum allowable quantities and the allowable locations of the tanks. There are additional installation requirements for these systems in the mechanical codes. Both the fire and mechanical codes reference NFPA 31.

When installed outside aboveground without any additional protection, tanks are limited to 660 gallons (2498 L). For tank sizes exceeding 660 gallons (2498 L), the installation must comply with NFPA 31. The standards used to certify these tanks are UL 142, Steel Aboveground Tanks for Flammable and Combustible Liquids, or UL 2085, Protected Aboveground Tanks for Flammable and Combustible Liquids, depending on whether or not the tank is protected. 

Indoor fuel oil storage tanks are certified per UL 80, Steel Tanks for Oil-Burner Fuels and Other Combustible Liquids, UL 142 or UL 2085. Selecting the type of tank depends on the expected quantities of fuel oil and whether an automatic fire sprinkler system protects a building. There are additional requirements for spill containment and fire separation of rooms containing fuel oil tanks from the remainder of the building. Tanks in basements are not permitted more than two stories below the grade plane.

Underground storage tanks are required to comply with either UL 58, Steel Underground Tanks for Flammable and Combustible Liquids, or UL 1316, Glass Fiber Reinforced Plastic Underground Storage Tanks for Petroleum Products, Alcohols and Alcohol-gasoline Mixtures.

Available resources

Code authorities, architects, contractors, users and interested parties can use UL Product iQ™ to help achieve compliance with the code requirements for fuel-fired equipment and fuel oil storage. Product iQ is a searchable database of UL Certified products, available at Product iQ is complimentary to use but does require a simple one-time registration. 

Search parameters include specific installation code sections and UL Standards. Product iQ also has guide information to aid in understanding the basic components of these various products and the applicable codes and standards to facilitate a reasonably safe and code-compliant installation.

Additional information on aboveground tanks

For further information or assistance, please contact UL’s Codes and Regulatory Services.


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