# Ventilation Air: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/ventilation-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 | IMC 2009, IECC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IMC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 9 (counted across the codes hosted here) |
| Wording identical across codes | No (compare before citing one code's wording under another) |

## Direct answer

Ventilation air is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space.” The IECC 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 9 chapters of this corpus, most often in Ventilation (IMC 2009), Fuel Gas (IRC 2009), Building Planning (IRC 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?

**Ventilation Air** — IMC 2009, Definitions:

> That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space.

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

*How the IMC 2009, IECC 2009 define ventilation 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 **Ventilation Air**, and the wording is not identical — read the version that governs your question.

| Code | Where it is defined | Definition |
| --- | --- | --- |
| IMC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space. |
| IECC 2009 | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | That portion of supply air that comes from outside (outdoors) plus any recirculated air that has been treated to maintain the desired quality of air within a designated space. |

## Where ventilation air is used in the code

The term appears in 9 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Ventilation](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md) | IMC 2009 | 9 |
| [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 7 |
| [Building Planning](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/building-planning.md) | IRC 2009 | 4 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | IECC 2009 | 2 |
| [Industrial Ovens](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/industrial-ovens.md) | IFC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) | IMC 2009 | 2 |
| [Duct Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/duct-systems.md) | IMC 2009 | 2 |
| [Means of Egress](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/means-of-egress.md) | IBC 2009 | 1 |
| [Means of Egress](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/means-of-egress.md) | IFC 2009 | 1 |

### The term in use

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

> The system to convey ventilation air shall be designed and installed in accordance with Chapter 6.

— [IMC 2009 §403.1](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md)

> Where combustion air is provided by the building's mechanical ventilation system, the system shall provide the specified combustion airrate in addition to the required ventilation air.

— [IRC 2009 §G2407.9.3](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md)

> Enclosed rooms or basements containing industrial ovens or furnaces shall be provided with combustion air in accordance with the International Mechanical Code and the International Fuel Gas Code, and with ventilation air in accordance with the International Mechanical Code.

— [IFC 2009 §2103.1](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/industrial-ovens.md)


## The terms ventilation air is built out of

The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what ventilation air covers:

- **[Recirculated Air](https://harth.build/resources/glossary/recirculated-air.md)** — IMC 2009: Air removed from a conditioned space and intended for reuse as supply air.
- **[Supply Air](https://harth.build/resources/glossary/supply-air.md)** — IRC 2009: Air delivered to a conditioned space through ducts or plenums from the heat exchanger of a heating, cooling or ventilating system.

## Ventilation 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 IMC | Definitions | |
| Read the definition in the adopted IECC | Definitions | |
| Re-check the requirement that uses it | Ventilation (IMC 2009) | |
| Re-check the requirement that uses it | Fuel Gas (IRC 2009) | |
| Re-check the requirement that uses it | Building Planning (IRC 2009) | |
| Re-check the requirement that uses it | Definitions (IECC 2009) | |
| Confirm the dependent definition | Recirculated Air | |
| Confirm the dependent definition | Supply 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)
- [Recirculated Air: Building Code Definition](https://harth.build/resources/glossary/recirculated-air.md)
- [Supply Air: Building Code Definition](https://harth.build/resources/glossary/supply-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 ventilation air?

The International Mechanical Code (IMC) 2009 defines it in Definitions as: “That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space.” 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.

### Do the I-Codes define ventilation air the same way?

No. IMC 2009, IECC 2009 all define the term, but the wording is not identical, and a difference in wording can change which requirements are triggered. The comparison table above sets the versions side by side so you can read the one that governs your question.

### Which parts of the code depend on ventilation air?

In this corpus the term is used across 9 chapters, led by Ventilation in the IMC 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 ventilation in a building?

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 ventilation air, which the IMC 2009 defines as “That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What does "ventilation air" mean?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IMC 2009 states, in Definitions: “That portion of supply air that comes from the outside (outdoors), plus any recirculated air that has been treated to maintain the desired quality of air within a designated space.” It is defined in IMC 2009, IECC 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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