# Vent Gases: Building Code Definition > How the IRC 2009 define vent gases, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/vent-gases/ - 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 (2009 editions transcribed in this corpus) | | Primary source | IRC 2009 Definitions (model text, not a jurisdiction's adopted text) | | Chapters using the term | 3 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Vent gases is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “Products of combustion from fuel-burning appliances, plus excess air and dilution air, in the venting system above the draft hood or draft regulator.” 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 3 chapters of this corpus, most often in Definitions (IRC 2009), Definitions (IMC 2009), Fuel Gas (IRC 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? **Vent Gases** — IRC 2009, Definitions: > Products of combustion from fuel-burning appliances, plus excess air and dilution air, in the venting system above the draft hood or draft regulator. ![Labeled code-term definition diagram: Vent Gases: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/vent-gases/diagram-1344.webp) *How the IRC 2009 define vent gases, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Vent Gases** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) chapter of the International Residential Code (IRC) 2009: > Products of combustion from fuel-burning appliances, plus excess air and dilution air, in the venting system above the draft hood or draft regulator. ## Where vent gases is used in the code The term appears in 3 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 10 | | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | IMC 2009 | 9 | | [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 9 | ### The term in use How the code actually writes about vent gases, quoted from the 2009 text hosted here: > and (2) whether or not the appliance generates flue or vent gases that might condense in the venting system. — [IRC 2009 §G2427.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) ## The terms vent gases is built out of The definition above leans on 5 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what vent gases covers: - **[Draft Regulator](https://harth.build/resources/glossary/draft-regulator.md)** — IRC 2009: A device that functions to maintain a desired draft in the appliance by automatically reducing the draft to the desired value. - **[Venting System](https://harth.build/resources/glossary/venting-system.md)** — IRC 2009: A continuous open passageway from the flue collar or draft hood of an appliance to the outside atmosphere for the purpose of removing flue or vent gases. - **[Dilution Air](https://harth.build/resources/glossary/dilution-air.md)** — IRC 2009: Air that enters a draft hood or draft regulator and mixes with flue gases. - **[Combustion](https://harth.build/resources/glossary/combustion.md)** — IRC 2009: In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light. - **[Excess Air](https://harth.build/resources/glossary/excess-air.md)** — IRC 2009: Air that passes through the combustion chamber and the appliance flue in excess of that which is theoretically required for complete combustion. ## Vent Gases: 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 | | | Re-check the requirement that uses it | Definitions (IRC 2009) | | | Re-check the requirement that uses it | Definitions (IMC 2009) | | | Re-check the requirement that uses it | Fuel Gas (IRC 2009) | | | Confirm the dependent definition | Draft Regulator | | | Confirm the dependent definition | Venting System | | | Confirm the dependent definition | Dilution Air | | | 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) - [Draft Regulator: Building Code Definition](https://harth.build/resources/glossary/draft-regulator.md) - [Venting System: Building Code Definition](https://harth.build/resources/glossary/venting-system.md) - [Dilution Air: Building Code Definition](https://harth.build/resources/glossary/dilution-air.md) - [Excess Air: Building Code Definition](https://harth.build/resources/glossary/excess-air.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 vent gases? The International Residential Code (IRC) 2009 defines it in Definitions as: “Products of combustion from fuel-burning appliances, plus excess air and dilution air, in the venting system above the draft hood or draft regulator.” 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 vent gases? In this corpus the term is used across 3 chapters, led by Definitions 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 are the code requirements for gas furnace venting? Furnace is a separate defined term. The IRC 2009 defines it as: “A completely self-contained heating unit that is designed to supply heated air to spaces remote from or adjacent to the appliance location.” That is not the same as vent gases, which the IRC 2009 defines as “Products of combustion from fuel-burning appliances, plus excess air and dilution air, in the venting system above the draft hood or draft regulator.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted. ### What is the code for vent piping for gas regulators? Piping is a separate defined term. The IRC 2009 defines it as: “Where used in this code, “piping” refers to either pipe or tubing, or both.” That is not the same as vent gases, which the IRC 2009 defines as “Products of combustion from fuel-burning appliances, plus excess air and dilution air, in the venting system above the draft hood or draft regulator.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fvent-gases%2F - View this page in a browser: https://harth.build/resources/glossary/vent-gases/ - All resources for agents: https://harth.build/llms.txt