What is Stainless 304 Alloy? | TSE Glossary

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Stainless 304 is an austenitic stainless steel containing approximately 18 percent chromium and 8 percent nickel, making it the workhorse alloy for wood-burning chimney liners and Class A chimney pipe. Its corrosion resistance handles the combustion byproducts of seasoned hardwood combustion, and its high-temperature performance covers normal wood-fire operating ranges. UL 1777 lists 304 stainless liners for solid-fuel use.

The chromium content in 304 forms a passive oxide layer that resists most acidic attack from wood-smoke condensates. Nickel improves toughness and high-temperature stability, allowing the alloy to retain strength at temperatures above 1500 degrees. For typical wood-burning service, where flue gases run between 300 and 700 degrees and condensates are mildly acidic, 304 provides decades of service when properly installed and maintained.

Where 304 falls short is in gas-burning applications. Natural gas combustion produces sulfuric and nitric acid condensates at lower flue temperatures, and these acids attack 304 over time. For gas inserts and gas log conversions, 316 stainless is specified because its molybdenum content resists chloride and acid corrosion. Sweeps match alloy to fuel during reline planning, and mismatching alloy to fuel is a common shortcut that produces premature liner failure.

DFW’s wood-burning fireplaces, particularly in older Lakewood, M Streets, and Highland Park homes, are well-served by insulated 304 stainless relines. The cooler humid winters keep condensate production modest, and 304 typically delivers 20-plus years of service when paired with annual sweeping. TSE installs 304 for solid-fuel only, switching to 316 the moment the homeowner converts to gas logs or a gas insert.

• [Stainless 316 alloy](/glossary/stainless-316-alloy/)
• [UL 1777 listed liner](/glossary/ul-1777-listed-liner/)
• [Class A chimney](/glossary/class-a-chimney/)
• [Cast-in-place liner](/glossary/cast-in-place-liner/)

• ASTM A240 stainless steel standard
• UL 1777 Standard for Chimney Liners
• NFPA 211 (2024), Section 10.6

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