# Flue, Appliance: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/flue-appliance/
- 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 Fuel Gas (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 4 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Flue, appliance is a defined term in the International Residential Code (IRC) 2009, in Fuel Gas. The code's own words are: “The passage(s) within an appliance through which combustion products pass from the combustion chamber of the appliance to the draft hood inlet opening on an appliance equipped with a draft hood or to the outlet of the appliance on an appliance not equipped with a draft hood.” 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 4 chapters of this corpus, most often in Fuel Gas (IRC 2009), Masonry (IBC 2009), Definitions (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?

**Flue, Appliance** — IRC 2009, Fuel Gas:

> The passage(s) within an appliance through which combustion products pass from the combustion chamber of the appliance to the draft hood inlet opening on an appliance equipped with a draft hood or to the outlet of the appliance on an appliance not equipped with a draft hood.

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

*How the IRC 2009 define flue, appliance, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Flue, Appliance** is defined once in this corpus, in the [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) chapter of the International Residential Code (IRC) 2009:

> The passage(s) within an appliance through which combustion products pass from the combustion chamber of the appliance to the draft hood inlet opening on an appliance equipped with a draft hood or to the outlet of the appliance on an appliance not equipped with a draft hood.

## Where flue, appliance is used in the code

The term appears in 4 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 | 12 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 6 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 5 |
| [Chimneys and Vents](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/chimneys-and-vents.md) | IMC 2009 | 3 |

### The term in use

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

> If a draft hood is not supplied by the appliance manufacturer where one is required, a draft hood shall be installed, shall be of a listed or approvedtype and, in the absence of other instructions, shall be of the same size as the appliance flue collar.

— [IRC 2009 §G2427.12.2.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md)

> The cross-sectional area of a flue serving a solid-fuel-burning appliance shall be not greater than three times the cross-sectional area of the appliance flue collar or flue outlet.

— [IMC 2009 §801.7](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/chimneys-and-vents.md)


## The terms flue, appliance 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 flue, appliance covers:

- **[Combustion Products](https://harth.build/resources/glossary/combustion-products.md)** — IRC 2009: Constituents resulting from the combustion of a fuel with the oxygen of the air, including the inert gases, but excluding excess air.
- **[Combustion Chamber](https://harth.build/resources/glossary/combustion-chamber.md)** — IRC 2009: The portion of an appliance within which combustion occurs.
- **[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.
- **[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 …
- **[Appliance](https://harth.build/resources/glossary/appliance.md)** — IRC 2009: Utilization equipment, normally built in standardized sizes or types, that is installed or connected as a unit to perform one or more functions such as clothes washing, air conditioning, food mixing, deep frying, etc.

## Flue, Appliance: 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 | |
| Re-check the requirement that uses it | Fuel Gas (IRC 2009) | |
| Re-check the requirement that uses it | Masonry (IBC 2009) | |
| Re-check the requirement that uses it | Definitions (IRC 2009) | |
| Re-check the requirement that uses it | Chimneys and Vents (IMC 2009) | |
| Confirm the dependent definition | Combustion Products | |
| Confirm the dependent definition | Combustion Chamber | |
| Confirm the dependent definition | Combustion | |
| 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)
- [Combustion Products: Building Code Definition](https://harth.build/resources/glossary/combustion-products.md)
- [Combustion Chamber: Building Code Definition](https://harth.build/resources/glossary/combustion-chamber.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 flue, appliance?

The International Residential Code (IRC) 2009 defines it in Fuel Gas as: “The passage(s) within an appliance through which combustion products pass from the combustion chamber of the appliance to the draft hood inlet opening on an appliance equipped with a draft hood or to the outlet of the appliance on an appliance not equipped with a draft hood.” 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 flue, appliance?

In this corpus the term is used across 4 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 the IRC code for chimney flashing?

Chimney is a separate defined term. The IBC 2009 defines it as: “A primarily vertical enclosure containing one or more passageways for conveying flue gases to the outside atmosphere.” That is not the same as flue, appliance, which the IRC 2009 defines as “The passage(s) within an appliance through which combustion products pass from the combustion chamber of the appliance to the draft hood inlet opening on an appliance equipped with a draft hood or to the outlet of the appliance on an …” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.

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