A chimney liner size calculator helps you determine the minimum liner diameter based on your appliance's BTU input rating and fuel type, following NFPA 211 guidelines.
Find on appliance label or manual
How to Size a Chimney Liner
Chimney liner sizing follows NFPA 211 tables based on appliance BTU input, flue height, and appliance connector pipe diameter. This calculator provides a general recommendation — always verify with a certified chimney professional before installation.
Key Sizing Principle
Higher BTU = more flue gas = larger liner needed. Taller chimneys create more natural draft, allowing slightly smaller liners. Short chimneys under 15 feet often need one size larger than the tables show. Always size up, not down — an undersized liner creates back-drafting and carbon monoxide hazards.
Consult a certified chimney sweep (CSIA) before installation.
Frequently Asked Questions
What chimney liner size do I need?
Liner size depends on your appliance's BTU input and type. Wood-burning appliances need round liners; gas appliances can use smaller Type B vent liners. This calculator uses NFPA 211 and appliance manufacturer guidance for sizing.
Can I use a smaller liner than my old chimney?
Yes, often required. Modern appliances run more efficiently and produce less flue gas, requiring smaller, properly sized liners. An oversized flue causes condensation and draft problems.
What is a chimney liner made of?
Common types: stainless steel (flexible or rigid), aluminum (gas only), cast-in-place (masonry repair), and clay tile (original in most masonry chimneys). Stainless steel flexible liner is the most versatile for relining.
How long does a chimney liner last?
Stainless steel liners last 15-25+ years with annual sweeping. Clay tile liners last 50+ years if undamaged. Always have a professional inspection before installing or assuming a liner is serviceable.
Is this calculator free?
Yes, completely free with no signup required.