# Combustion Air: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/combustion-air/
- 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 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 20 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Combustion air is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “The air provided to fuel-burning equipmentincluding air for fuel combustion, draft hood dilution and ventilation of the equipment enclosure.” The IMC 2009 words it differently, in Definitions: “Air necessary for complete combustion of a fuel, including theoretical air and excess air.” The IMC 2009 defines the same term with different wording, so the controlling text depends on which code governs the question in front of you — the comparison below sets the versions side by side. The term is used in 20 chapters of this corpus, most often in Fuel Gas (IRC 2009), Combustion Air (IRC 2009), Combustion Air (IMC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.

*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 Air** — IRC 2009, Definitions:

> The air provided to fuel-burning equipmentincluding air for fuel combustion, draft hood dilution and ventilation of the equipment enclosure.

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

*How the IRC 2009, IMC 2009 define combustion air, 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 Air**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IRC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | The air provided to fuel-burning equipmentincluding air for fuel combustion, draft hood dilution and ventilation of the equipment enclosure. |
| IMC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | Air necessary for complete combustion of a fuel, including theoretical air and excess air. |

## Where combustion air is used in the code

The term appears in 20 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 | 65 |
| [Combustion Air](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/combustion-air.md) | IRC 2009 | 13 |
| [Combustion Air](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/combustion-air.md) | IMC 2009 | 12 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 8 |
| [Chimneys and Fireplaces](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/chimneys-and-fireplaces.md) | IRC 2009 | 8 |
| [General Regulations](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/general-regulations.md) | IMC 2009 | 7 |
| [Refrigeration](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/refrigeration.md) | IMC 2009 | 6 |
| [Chimneys and Vents](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/chimneys-and-vents.md) | IRC 2009 | 5 |
| [Heating and Cooling Equipment](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/heating-and-cooling-equipment.md) | IRC 2009 | 4 |
| [Boilers and Water Heaters](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/boilers-and-water-heaters.md) | IRC 2009 | 3 |
| [Special Fuel-burning Equipment](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/special-fuel-burning-equipment.md) | IRC 2009 | 3 |
| [Interior Environment](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/interior-environment.md) | IBC 2009 | 2 |

_8 further chapters mention the term._

### The term in use

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

> Where used, a drafthoodor a barometric draft regulator shall be installed in the same room or enclosure as the applianceserved so as to prevent any difference in pressure between the hood or regulator and the combustion air supply.

— [IRC 2009 §G2407.3](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md)

> Solid-fuel-burning appliances shall be provided with combustion air in accordance with the appliance manufacturer's installation instructions.

— [IRC 2009 §M1701.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/combustion-air.md)

> Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer's instructions.

— [IBC 2009 §2111.13.1](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md)


## The terms combustion air 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 combustion air covers:

- **[Ventilation](https://harth.build/resources/glossary/ventilation.md)** — IBC 2009: The natural or mechanical process of supplying conditioned or unconditioned air to, or removing such air from, any space.
- **[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.
- **[Draft Hood](https://harth.build/resources/glossary/draft-hood.md)** — IRC 2009: A nonadjustable device built into an appliance, or made as part of the vent connector from an appliance, that is designed to (1) provide for ready escape of the flue gases from the appliance in the event of no draft …
- **[Equipment](https://harth.build/resources/glossary/equipment.md)** — IRC 2009: All piping, ducts, vents, control devices and other components of systems other than appliances that are permanently installed and integrated to provide control of environmental conditions for buildings.

## Combustion Air: 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 IMC | Definitions | |
| Re-check the requirement that uses it | Fuel Gas (IRC 2009) | |
| Re-check the requirement that uses it | Combustion Air (IRC 2009) | |
| Re-check the requirement that uses it | Combustion Air (IMC 2009) | |
| Re-check the requirement that uses it | Masonry (IBC 2009) | |
| Confirm the dependent definition | Ventilation | |
| Confirm the dependent definition | Combustion | |
| Confirm the dependent definition | Excess 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)
- [Ventilation: Building Code Definition](https://harth.build/resources/glossary/ventilation.md)
- [Excess Air: Building Code Definition](https://harth.build/resources/glossary/excess-air.md)
- [Draft Hood: Building Code Definition](https://harth.build/resources/glossary/draft-hood.md)
- [Combustion: Building Code Definition](https://harth.build/resources/glossary/combustion.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 air?

The International Residential Code (IRC) 2009 defines it in Definitions as: “The air provided to fuel-burning equipmentincluding air for fuel combustion, draft hood dilution and ventilation of the equipment enclosure.” 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 air?

In this corpus the term is used across 20 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 considered combustion air?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “The air provided to fuel-burning equipmentincluding air for fuel combustion, draft hood dilution and ventilation of the equipment enclosure.” 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.

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