# Combustion: Building Code Definition

> How the IRC 2009, IMC 2009 define combustion, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/combustion/
- 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, IMC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IRC 2009 Fuel Gas (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 48 (counted across the codes hosted here) |
| Wording identical across codes | Yes (compare before citing one code's wording under another) |

## Direct answer

Combustion is a defined term in the International Residential Code (IRC) 2009, in Fuel Gas. The code's own words are: “In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light.” The IMC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 48 chapters of this corpus, most often in Fuel Gas (IRC 2009), Definitions (IMC 2009), Masonry (IBC 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?

**Combustion** — IRC 2009, Fuel Gas:

> In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light.

![Labeled code-term definition diagram: Combustion: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/combustion/diagram-1344.webp)

*How the IRC 2009, IMC 2009 define combustion, 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 **Combustion**, in identical words.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IRC 2009 | [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light. |
| IMC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light. |

## Where combustion is used in the code

The term appears in 48 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 123 |
| [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | IMC 2009 | 46 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 23 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 22 |
| [Fire and Smoke Protection Features](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) | IBC 2009 | 18 |
| [Use and Occupancy Classification](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/use-and-occupancy-classification.md) | IBC 2009 | 18 |
| [Refrigeration](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/refrigeration.md) | IMC 2009 | 15 |
| [Chimneys and Vents](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/chimneys-and-vents.md) | IMC 2009 | 14 |
| [Combustion Air](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/combustion-air.md) | IRC 2009 | 14 |
| [Combustion Air](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/combustion-air.md) | IMC 2009 | 13 |
| [Chimneys and Fireplaces](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/chimneys-and-fireplaces.md) | IRC 2009 | 13 |
| [Building Services and Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/building-services-and-systems.md) | IFC 2009 | 11 |

_36 further chapters mention the term._

### The term in use

How the code actually writes about combustion, quoted from the 2009 text hosted here:

> The requirements for combustion and dilution air for gas-fired appliances shall be governed by Section G2407.

— [IRC 2009 §G2404.2](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md)

> Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.

— [IBC 2009 §2111.13](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md)

> Noncombustible penetrating items that connect not more than three stories are permitted, provided that the annular space is filled to resist the free passage of flame and the products of combustion with an approved noncombustible material or with a fill, void or cavity material that is tested and classified for use in through-penetration firestop systems.

— [IBC 2009 §713.4.2](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md)

## Combustion: 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 | Fuel Gas | |
| Read the definition in the adopted IMC | Definitions | |
| Re-check the requirement that uses it | Fuel Gas (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IMC 2009) | |
| Re-check the requirement that uses it | Masonry (IBC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| 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)
- [Code Official: Building Code Definition](https://harth.build/resources/glossary/code-official.md)
- [Code: Building Code Definition](https://harth.build/resources/glossary/code.md)
- [Fuel Gas: Building Code Definition](https://harth.build/resources/glossary/fuel-gas.md)
- [Vent: Building Code Definition](https://harth.build/resources/glossary/vent.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 combustion?

The International Residential Code (IRC) 2009 defines it in Fuel Gas as: “In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light.” 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 combustion?

In this corpus the term is used across 48 chapters, led by Fuel Gas 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 simple definition of combustion?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Fuel Gas: “In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light.” It is defined in IRC 2009, IMC 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 the definition of a building code?

Building is a separate defined term. The IBC 2009 defines it as: “Any structure used or intended for supporting or sheltering any use or occupancy.” That is not the same as combustion, which the IRC 2009 defines as “In the context of this code, refers to the rapid oxidation of fuel accompanied by the production of heat or heat and light.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

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