UL 1738 Venting: For the Certainty of Safety With Gas-Burning Appliances

Why UL Matters: The Importance of Special Gas Venting

Did you know the UL mark is more than 100 years old? Its first standard for “Tin Clad Fire Doors” was published back in 1903. Three years later, in 1906, UL started a broader Label Service to enhance product electrical and fire safety.

Today, the UL mark can be found on 22 billion products annually. The mark is the most accepted certification mark in the United States and addresses a broad range of safety issues. Those issues still include electrical and fire safety but can also include hazardous substances, water quality, food safety and more. To earn — and keep — that mark isn’t simple. Products undergo rigorous tests under challenging conditions. Many fail to earn UL certification. Others don’t even qualify, such as field-fabricated venting systems, since they aren’t constructed in a controlled, UL-inspected environment. Customers of products that are not UL-certified use them at their own risk.

At Schebler, all our chimney and venting products are prefabricated and produced under strict supervision to ensure they meet every taxing UL requirement. That’s why we say Schebler brings you certainty — the certainty of safety, quality and reliability.

UL 1738 Venting: The Standard for Safety

The UL 1738 standard addresses venting systems for gas-burning appliances, categories II, III and IV. The standard also assumes the appliances that have been installed in accordance with NFPA 54 and with codes, such as the BOCA National Mechanical Code, the Standard Mechanical Code, the Uniform Mechanical Code and any local codes.

These venting systems must be constructed with very specific requirements. They must be made of corrosion-resistant materials or have a corrosion-resistant finish and have the rigidity, durability and resistance to heat that are necessary for the intended application. Those materials may include stainless steel, porcelain-coated steel, aluminum and non-metallic materials, such as cast and fired refractory. Non-metallic vent gas conduit materials can also be used if they have sufficient strength and rigidity for the intended application, won’t soften or melt when exposed to the temperatures anticipated during appliance operation or crack when exposed to outdoor or indoor temperatures, as applicable.

Additional requirements include the following:

• The venting system must be assembled with all parts before inspection, including joints, firestop spacers, thimbles, support assembly, radiation shields, vent termination or caps, drain fittings and appliance adapters.
• Joints and seams for use with Category III or IV appliances must be gas tight as determined by a leakage test.
• All parts must be assembled per the manufacturer’s installation instructions.

UL 1738 Venting Testing and Requirements

All factory-built venting systems that meet UL 1738 venting requirements undergo rigorous tests. Each test must be carefully observed and recorded. They include tests involving the size and shape of the system (e.g., round, oval, or other), its height and length, the minimum required clearance to combustible construction, enclosure in stud space, single or multistory building or buildings and temperature ratings.

As a result of the tests, none of the system’s parts can be damaged or distorted, including all coatings and finishes. There can be no impairment of the surface’s reflectivity or insulation, no burning or scaling must be evident and no parts can be softened, melted or moved. In other words, the equipment should be 100% intact.

The many tests include, but are not limited to, the following.

• Temperature Measurements

Separate temperature tests of the thermocouple, vent gas and structure help ensure every part of the system is fire safe.

• Draft Loss Test and Wind Effects Test

These ensure a cap or vent termination does not significantly impede the flow of vent gases in still air or under wind conditions.

• Vertical Support Test

This ensures an assembly intended to support a vertical venting system won’t be damaged or the security of its attachment to the building structure won’t be impaired when loaded with heavy weight.

• Impact test

This ensures a venting system or its parts won’t break, disassemble or become damaged due to a significant impact.

• Load Test for Vent Elbows

This confirms the integrity of the elbow supports. Specifically, it ensures the elbow support won’t break, disassemble or become damaged when subjected to a load equivalent to 4x the weight of the longest venting system section between adjacent supports. 

• Vent Joint Load Test

This load test ensures a vent joint of an offset vent won’t loosen, break, or disassemble when subjected to a load equivalent to 4x the weight of the maximum length between the supports.

• Wind Load Test

This tests wind resistance. Specifically, the test ensures a roof assembly can withstand, without damage or opening of joints, a load equivalent to 30 pounds per square foot (146 kg/m²) of exposed area applied to any surface extending above the roof.

• Lateral Supports Test

This 60-minute test ensures exterior vent installations can withstand significant loads without damage, displacement, separation or distortion.

• Pressure Test

This ensures vent sections with joints can withstand, without rupture, an internal air pressure of 2-1/2 times the manufacturer’s rated positive pressure.

• Leakage Test

This ensures the system is leak-free, including in every joint and connection.

• Joint Sealing Compound Test

This ensures the joint sealing compound used to seal or secure won’t crack, soften, melt or show other evidence of deterioration even during extreme temperatures. 

• Condensate Conditioning Test

In this test, materials are immersed in a deionized water solution for up to 180 days to ensure there is no lack of tensile strength.

Other tests include an Induced Updraft Test, Longitudinal Force Test, Torsion Test, Freezing and Thawing Test, Rain Test, Cemented Joint Test, Condensate Exposure Test, Vent Sag Test, Bending Test and a Joint Tightness Test.

The Certainty of UL Listed Safety

At Schebler, we have been UL certified since 1994 and have never received a single major violation. This is just one reason why prefabricated products are safer than those made in the field and why our customers appreciate and rely on the Certainty of Schebler.

Contact us to learn more about our chimney and venting solutions.