What is a Flue and How is it Different from a Chimney?
A flue is a single internal duct or passage through which smoke, exhaust, and combustion gases travel to the outside atmosphere. A chimney is the outer structural enclosure (built from masonry, metal, or factory-built materials) that contains one or more flues inside it. Refer to NFPA 211 2024 edition for more information about the nuances of chimneys, flues and more.
Below is an image of a flue tile section in front of our shop. A series of flue tiles go inside of a chimney. (Flue is inside and chimney is outside.)
How Chimneys and Flue Tiles Work Together?
Think of the chimney as the building or pipe on the outside, and the flue as the hallway on the inside. They work together to create a cohesive system. Flue tiles are not needed for a pre-insulated wood liner because the liner is creating a new venting system.
Breaking out flue tiles is a common practice when installing a new insulated wood insert liner is a masonry fireplace. Be mindful when working with a chimney sweep to repair a chimney that could be relined for a new wood fireplace insert without an expensive chimney rebuild.
| Feature | Flue | Chimney |
| Definition | The inner passage or liner conveying exhaust gases. | The outer structure housing the flue(s). |
| Function | Directs smoke and gases up and out safely. | Provides structural support and isolates heat from the building. |
| Multiplicity | A single chimney can contain multiple flues. | A single structure surrounding the flue liners. |
| Material | Clay tile, stainless steel liner, or appliance pipe. | Brick, stone, concrete block, or double/triple-wall metal. |
Chimney is Outside and Flue is Inside
The flue is the specific inner channel that carries exhaust gases away, while the chimney is the overall protective physical structure housing it. When estimating job scope for unit installations or retrofits, ensuring flue sizing matches the unit collar and confirming code clearances per NFPA 211 (2024) is required for health and safety.
What’s Next for My Flue or Chimney Repair?
- Typical Cost Ranges for Venting & Flue Work: Stainless Steel Flue Relining: $1,500 to $5,500 (Includes continuous stainless liner installation for inserts/stoves. Extra cost often due to creosote remediation.)
- Factory-Built Class A Chimney Installation: $2,500 to $8,000+ depending on floor penetrations and height.
- Standard Full Installation Labor/Materials: $1,000 – $9,999+
- Next Steps: Get a Level II camera inspection to verify flue integrity before doing any permanent installation work.
- Hire an NFI Certified Fireplace Installation Company
Who is The Stove Shop Fireplace Experts?
The Stove Shop Fireplace Experts in Phoenixville, PA helps our customers stay warm and save money. We install and service fireplaces and stoves fueled by wood, natural gas, propane and pellet. Check out our fireplaces and stoves product page!
Our goal with this information is to help you make the best decision for your home. Please contact us at The Stove Shop in Phoenixville, PA or give us a call 610-935-9334 for more info.
