Building Code Glossary
Type L Vent: Building Code Definition
How the IRC 2009 define type l vent, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Type L vent is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.” No other I-Code in this corpus defines it, so the IRC 2009 definition is the one to work from. The term is used in 7 chapters of this corpus, most often in Chimneys and Vents (IRC 2009), Chimneys and Vents (IMC 2009), Definitions (IMC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted. Record the jurisdiction, the adopted edition, the application date and any local amendment that rewrites the definition before you use it on a live project, because a term redefined by amendment changes every requirement that depends on it.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Type L Vent — IRC 2009, Definitions:
A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.
What must be verified before using this guidance?
Type L Vent is defined once in this corpus, in the Definitions chapter of the International Residential Code (IRC) 2009:
A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.
Where type l vent is used in the code
The term appears in 7 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Chimneys and Vents | IRC 2009 | 9 |
| Chimneys and Vents | IMC 2009 | 4 |
| Definitions | IMC 2009 | 4 |
| Chimneys and Fireplaces | IRC 2009 | 4 |
| Masonry | IBC 2009 | 3 |
| Fuel Gas | IRC 2009 | 3 |
| Definitions | IRC 2009 | 2 |
The term in use
How the code actually writes about type l vent, quoted from the 2009 text hosted here:
Connectors for oil and solid-fuel-burning appliances shall be constructed of factory-built chimney material, Type L vent material or single-wall metal pipe having resistance to corrosion and heat and thickness not less than that of galvanized steel as specified in Table MI803.2.
Flue lining and vent systems for use in masonry chimneys with oil-fired appliances approved for use with Type L vent shall be limited to flue lining systems complying with Section 2113.11.1 and listed chimney liners complying with UL 641 (see Section 2113.11.1.5 for marking).
The terms type L vent is built out of
The definition above leans on 3 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what type L vent covers:
- Labeled — IBC 2009: Equipment, materials or products to which has been affixed a label, seal, symbol or other identifying mark of a nationally recognized testing laboratory, inspection agency or other organization concerned with product evaluation that maintains periodic inspection of the production of …
- Venting — IRC 2009: Removal of combustion products to the outdoors.
- Listed — IBC 2009: Equipment, materials, products or services included in a list published by an organization acceptable to the code official and concerned with evaluation of products or services that maintains periodic inspection of production of listed equipment or materials or periodic evaluation …
Type L Vent: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IRC | Definitions | |
| Re-check the requirement that uses it | Chimneys and Vents (IRC 2009) | |
| Re-check the requirement that uses it | Chimneys and Vents (IMC 2009) | |
| Re-check the requirement that uses it | Definitions (IMC 2009) | |
| Re-check the requirement that uses it | Chimneys and Fireplaces (IRC 2009) | |
| Confirm the dependent definition | Labeled | |
| Confirm the dependent definition | Venting | |
| Confirm the dependent definition | Listed | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
- Explore all glossary guidance
- Venting: Building Code Definition
- Labeled: Building Code Definition
- Listed: Building Code Definition
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of type l vent?
The International Residential Code (IRC) 2009 defines it in Definitions as: “A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on type l vent?
In this corpus the term is used across 7 chapters, led by Chimneys and Vents in the IRC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What is a type L vent?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.” It is defined in IRC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
What are the vent requirements for a gas fireplace?
Fireplace is a separate defined term. The IBC 2009 defines it as: “A hearth and fire chamber or similar prepared place in which a fire may be made and which is built in conjunction with a chimney.” That is not the same as type L vent, which the IRC 2009 defines as “A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
What is type L venting?
Venting is a separate defined term. The IRC 2009 defines it as: “Removal of combustion products to the outdoors.” That is not the same as type L vent, which the IRC 2009 defines as “A listed and labeled vent conforming to UL 641 for venting oil-burning appliances listed for use with Type L vents or with gas appliances listed for use with Type B vents.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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