# Circuit Vent: Building Code Definition > How the IRC 2009, IPC 2009 define circuit vent, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/circuit-vent/ - Last updated: 2026-09-07 - Data source: 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. ## Key facts | Fact | Value | | --- | --- | | Defined in | IRC 2009, IPC 2009 (2009 editions transcribed in this corpus) | | Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) | | Chapters using the term | 4 (counted across the codes hosted here) | | Wording identical across codes | Yes (compare before citing one code's wording under another) | ## Direct answer Circuit vent is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery.” The IPC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 4 chapters of this corpus, most often in Vents (IRC 2009), Vents (IPC 2009), Definitions (IPC 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](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.* ## What does this term mean? **Circuit Vent** — IRC 2009, Definitions: > A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery. ![Labeled code-term definition diagram: Circuit Vent: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/circuit-vent/diagram-1344.webp) *How the IRC 2009, IPC 2009 define circuit vent, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? Two of the I-Codes in this corpus define **Circuit Vent**, in identical words. | Code | Where it is defined | Definition | | --- | --- | --- | | IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery. | | IPC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery. | ## Where circuit vent is used in the code The term appears in 4 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Vents](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/vents.md) | IRC 2009 | 17 | | [Vents](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/vents.md) | IPC 2009 | 16 | | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | IPC 2009 | 1 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 | ### The term in use How the code actually writes about circuit vent, quoted from the 2009 text hosted here: > The circuit vent connection shall be located between the two most upstream fixture drains. — [IRC 2009 §P3110.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/vents.md) > Each group ofa maximum of eight fixtures shall be considered a separate circuit vent and shall conform to the requirements of this section. — [IPC 2009 §911.1.1](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/vents.md) ## The terms circuit vent is built out of The definition above leans on 1 other defined term. Each carries its own code definition, and a local amendment to any of them changes what circuit vent covers: - **[Branch](https://harth.build/resources/glossary/branch.md)** — IRC 2009: Any part of the piping system other than a riser, main or stack. ## Circuit Vent: what to open, and in what order Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows. | Check | Where | Confirmed | | --- | --- | --- | | Read the definition in the adopted IRC | Definitions | | | Read the definition in the adopted IPC | Definitions | | | Re-check the requirement that uses it | Vents (IRC 2009) | | | Re-check the requirement that uses it | Vents (IPC 2009) | | | Re-check the requirement that uses it | Definitions (IPC 2009) | | | Re-check the requirement that uses it | Definitions (IRC 2009) | | | Confirm the dependent definition | Branch | | | 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](https://harth.build/resources/glossary.md) - [Branch: Building Code Definition](https://harth.build/resources/glossary/branch.md) - [Building: Building Code Definition](https://harth.build/resources/glossary/building.md) - [Construction Documents: Building Code Definition](https://harth.build/resources/glossary/construction-documents.md) - [Registered Design Professional: Building Code Definition](https://harth.build/resources/glossary/registered-design-professional.md) ## 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](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. ### Source links - [codes.iccsafe.org](https://codes.iccsafe.org/codes) - [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/) ## Frequently asked questions ### What is the code definition of circuit vent? The International Residential Code (IRC) 2009 defines it in Definitions as: “A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery.” 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 circuit vent? In this corpus the term is used across 4 chapters, led by 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 the definition of a circuit vent? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery.” It is defined in IRC 2009, IPC 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 is a circuit vent in plumbing? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A vent that connects to a horizontal drainage branch and vents two traps to a maximum of eight traps or trapped fixtures connected into a battery.” It is defined in IRC 2009, IPC 2009. It is not the same as Plumbing, which the IRC 2009 defines separately as “For the purpose of this code, plumbing refers to those installations, repairs, maintenance and alterations regulated by Chapters 25 through 33.” 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fcircuit-vent%2F - View this page in a browser: https://harth.build/resources/glossary/circuit-vent/ - All resources for agents: https://harth.build/llms.txt