A flue is the inner passage that carries smoke and combustion gases out of your home. A chimney is the full structure that encloses that flue. In short: the chimney is the shell, and the flue is the channel inside it. Most homes have one chimney with one or more flues running up through it.
| Term | What it is | Everyday example |
|---|---|---|
| Flue | The inner passage that carries smoke and gases up and out | The stainless liner or clay tile inside the brick |
| Chimney | The whole structure that surrounds and supports the flue | The brick or metal stack you see above the roof |
So what is the real difference?
- Chimney: the full outer structure, often brick or insulated metal, that houses the flue and rises above the roof.
- Flue: the internal pipe or passage inside the chimney that carries smoke and gases upward and out.
A flue is always part of a chimney system. A chimney is not necessarily a flue: it is the larger structure that contains one or more flues. Chimneys handle the structural and weather-protection side of venting; flues handle the high-temperature, corrosive gases produced by combustion.
Why getting the terms right matters
- Ordering a "chimney pipe" online may get you only the outer housing when what you need is a flue liner (aka chimney liner).
- Building codes specify clearances around the flue, not just the chimney structure.
- Insurers often require a properly installed flue liner before covering a wood stove or fireplace.
- Stove manufacturers specify flue diameter, not chimney diameter, in their installation instructions.
U.S. code: clearances and chimney height
| Standard | Rule |
|---|---|
| Single-wall stove pipe (NFPA 211) | Per NFPA 211, single-wall stove pipe must maintain at least 18 inches of clearance from any combustible wall, ceiling, or framing. |
| Double-wall stove pipe (NFPA 211) | Per NFPA 211, double-wall stove pipe is rated for reduced clearances typically 6 inches from combustible walls and 8 inches from ceilings (verify exact clearance with the specific UL-listed product). |
| Class A chimney pipe (UL 103 HT) | Class A insulated chimney pipe, when UL 103 HT-listed for wood-burning, maintains a minimum of 2 inches clearance to combustibles per the standard listing. Always verify the exact clearance specified by the manufacturer's UL listing for the specific product. |
| Chimney height - 3-2-10 rule (NFPA 211 / IRC R1003.9) | The 3-2-10 rule requires that a chimney extend at least 3 feet above the highest point where it passes through the roof, AND at least 2 feet higher than any portion of the building, structure, or obstruction within a 10-foot horizontal radius. |
Common flue liner types
Flexible stainless steel liners are the usual choice for relining an older masonry chimney because they navigate bends rigid liners cannot. Rigid stainless liners suit straight runs and new construction. For a complete relining solution, see our chimney liner kits. If you are building a new run, a Class A insulated chimney pipe system combines flue and structure in one UL 103 HT listed assembly, and our full range of wood stove chimney kits ships as complete matched systems.
Get your flue sized right, free
Rather than guess across competing brands, we carry one curated, fully matched product line and pair it with dedicated technical advice from a real chimney specialist. Our flue and chimney design help is free: tell us your stove and layout and we will spec the complete, code-compliant system you need. Every system is backed by a limited warranty and a 14-day no-questions-asked return policy, with US-based support.
Getting the flue sized right is what makes a stove draft well and stay safe. Tell us your stove and layout and get free flue-design help: we spec the complete, code-compliant system for your setup. Or talk it through with a specialist at 888-834-0880. When you know your size, the matched chimney liner kits come as one system.
Need More Information?
Visit our frequently asked questions, browse the wood stove pipe installation guides, or get free expert advice from one of our chimney specialists.
