# Exhaust System: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/exhaust-system/
- 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 (2009 editions transcribed in this corpus) |
| Primary source | IMC 2009 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 22 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Exhaust system is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.” No other I-Code in this corpus defines it, so the IMC 2009 definition is the one to work from. The term is used in 22 chapters of this corpus, most often in Exhaust Systems (IMC 2009), Highly Toxic and Toxic Materials (IFC 2009), Special Detailed Requirements Based on Use and Occupancy (IBC 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?

**Exhaust System** — IMC 2009, Definitions:

> An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.

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

*How the IMC 2009 define exhaust system, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Exhaust System** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) chapter of the International Mechanical Code (IMC) 2009:

> An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.

## Where exhaust system is used in the code

The term appears in 22 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Exhaust Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/exhaust-systems.md) | IMC 2009 | 128 |
| [Highly Toxic and Toxic Materials](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/highly-toxic-and-toxic-materials.md) | IFC 2009 | 23 |
| [Special Detailed Requirements Based on Use and Occupancy](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/special-detailed-requirements-based-on-use-and-occupancy.md) | IBC 2009 | 17 |
| [Exhaust Systems](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/exhaust-systems.md) | IRC 2009 | 14 |
| [Ventilation](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/ventilation.md) | IMC 2009 | 9 |
| [Duct Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/duct-systems.md) | IMC 2009 | 8 |
| [Refrigeration](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/refrigeration.md) | IMC 2009 | 7 |
| [Fire and Smoke Protection Features](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) | IBC 2009 | 6 |
| [Compressed Gases](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/compressed-gases.md) | IFC 2009 | 6 |
| [Flammable and Combustible Liquids](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/flammable-and-combustible-liquids.md) | IFC 2009 | 6 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-protection-systems.md) | IBC 2009 | 5 |
| [Fire Protection Systems](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/fire-protection-systems.md) | IFC 2009 | 5 |

_10 further chapters mention the term._

### The term in use

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

> The air removed by every mechanical exhaust system shall be discharged outdoors at a point where it will not cause a nuisance and not less than the distances specified in Section 501.2.1.

— [IMC 2009 §501.2](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/exhaust-systems.md)

> Gas cabinets and exhausted enclosures shall be located in gas rooms and connected to an exhaust system.

— [IFC 2009 §3704.2.2.3.1](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/highly-toxic-and-toxic-materials.md)

> Where provided, each compartment shall have an air supply and an exhaust system independent of the other compartments.

— [IBC 2009 §405.4.2](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/special-detailed-requirements-based-on-use-and-occupancy.md)


## Exhaust System compared with Supply Air System

These two are the closest pair in the 2009 I-Codes: about 62 per cent of their defining words are the same. The code states both and compares neither, so the difference is worth naming.

| | Wording unique to it |
| --- | --- |
| **Exhaust System** (IMC 2009) | hoods, exhausted, outdoor, atmosphere |
| [Supply Air System](https://harth.build/resources/glossary/supply-air-system.md) (IMC 2009) | heated, cooled, supply, unit, see, also, return, system |

Everything else in the two definitions is shared. If a project turns on which of the two applies, those words are the whole of the test — and a local amendment that edits one of them without editing the other moves the boundary between exhaust system and supply air system.

## Exhaust System: 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 | |
| Re-check the requirement that uses it | Exhaust Systems (IMC 2009) | |
| Re-check the requirement that uses it | Highly Toxic and Toxic Materials (IFC 2009) | |
| Re-check the requirement that uses it | Special Detailed Requirements Based on Use and Occupancy (IBC 2009) | |
| Re-check the requirement that uses it | Exhaust Systems (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)
- [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)
- [Dwelling Unit: Building Code Definition](https://harth.build/resources/glossary/dwelling-unit.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 exhaust system?

The International Mechanical Code (IMC) 2009 defines it in Definitions as: “An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.” 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 exhaust system?

In this corpus the term is used across 22 chapters, led by Exhaust Systems 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 are the code requirements for exhaust fan venting?

Venting is a separate defined term. The IRC 2009 defines it as: “Removal of combustion products to the outdoors.” That is not the same as exhaust system, which the IMC 2009 defines as “An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

### What is an exhaust system in a house?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IMC 2009 states, in Definitions: “An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.” It is defined in 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 an exhaust ventilation system?

Ventilation is a separate defined term. The IBC 2009 defines it as: “The natural or mechanical process of supplying conditioned or unconditioned air to, or removing such air from, any space.” That is not the same as exhaust system, which the IMC 2009 defines as “An assembly of connected ducts, plenums, fittings, registers, grilles and hoods through which air is conducted from the space or spaces and exhausted to the outdoor atmosphere.” — 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%2Fexhaust-system%2F
- View this page in a browser: https://harth.build/resources/glossary/exhaust-system/
- All resources for agents: https://harth.build/llms.txt