How it works

The cap is fabricated from stainless steel, galvanized steel, or copper, with corner legs that anchor to the crown via masonry anchors or expansion bolts. The roof of the cap projects beyond the chimney edge to shed water, and stainless mesh sidewalls provide the spark and animal barriers. The vertical clearance between the cap roof and the flue tile tops must be at least equal to the diameter of the largest flue to avoid restricting draft.

Multi-flue caps are appropriate for masonry chimneys with two or more flues serving separate appliances, such as a combination of fireplace and water heater flues, or two fireplaces in a duplex configuration. Sweeps verify the cap clearance to flue tile during inspection because undersized clearances impair draft. Custom-fabricated caps deliver the best fit and durability, while stock units may not align well with non-standard chimney dimensions.

DFW context

DFW masonry chimneys with multiple flues are most common in older Highland Park, M Streets, and East Dallas homes where one chimney served both fireplace and gravity furnace, or two adjacent fireplaces. TSE custom-fabricates multi-flue caps in stainless or copper to match each chimney’s crown dimensions, with welded seams that resist hail and wind damage. The June 2025 hailstorms damaged thousands of stock multi-flue caps across the region, and replacements are now custom by default.

Related terms

• [Single-flue cap](/glossary/single-flue-cap/)
• [Custom copper cap](/glossary/custom-copper-cap/)
• [Crown](/glossary/crown/)
• [Spark arrestor](/glossary/spark-arrestor/)

Sources

• NFPA 211 (2024), Section 10.4.5
• IRC 2021, Section R1003.9.1
• CSIA Reference Manual