# Masonry Heater: Building Code Definition

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

- Canonical: https://harth.build/resources/glossary/masonry-heater/
- 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 Definitions (model text, not a jurisdiction's adopted text) |
| Chapters using the term | 6 (counted across the codes hosted here) |
| Wording identical across codes | Single code (compare before citing one code's wording under another) |

## Direct answer

Masonry heater is a defined term in the International Residential Code (IRC) 2009, in Definitions. The code's own words are: “A masonry heater is a solid fuel burning heating appliance constructed predominantly of concrete or solid masonry having a mass of at least 1,100 pounds (500 kg), excluding the chimney and foundation. It is designed to absorb and store a substantial portion of heat from a fire built in the firebox by routing exhaust gases …” 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 6 chapters of this corpus, most often in Chimneys and Fireplaces (IRC 2009), Masonry (IBC 2009), Structural Tests and Special Inspections (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?

**Masonry Heater** — IRC 2009, Definitions:

> A masonry heater is a solid fuel burning heating appliance constructed predominantly of concrete or solid masonry having a mass of at least 1,100 pounds (500 kg), excluding the chimney and foundation. It is designed to absorb and store a substantial portion of heat from a fire built in the firebox by routing exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes at least one 180-degree (3.14-rad) change in flow direction before entering the chimney and which deliver heat by radiation through the masonry surface of the heater.

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

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

## What must be verified before using this guidance?

**Masonry Heater** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) chapter of the International Residential Code (IRC) 2009:

> A masonry heater is a solid fuel burning heating appliance constructed predominantly of concrete or solid masonry having a mass of at least 1,100 pounds (500 kg), excluding the chimney and foundation. It is designed to absorb and store a substantial portion of heat from a fire built in the firebox by routing exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes at least one 180-degree (3.14-rad) change in flow direction before entering the chimney and which deliver heat by radiation through the masonry surface of the heater.

## Where masonry heater is used in the code

The term appears in 6 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.

| Chapter | Code | Mentions |
| --- | --- | --- |
| [Chimneys and Fireplaces](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/chimneys-and-fireplaces.md) | IRC 2009 | 20 |
| [Masonry](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md) | IBC 2009 | 18 |
| [Structural Tests and Special Inspections](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/structural-tests-and-special-inspections.md) | IBC 2009 | 2 |
| [Specific Appliances, Fireplaces and Solid Fuel-burning Equipment](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/specific-appliances-fireplaces-and-solid-fuel-burning-equipment.md) | IMC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 2 |
| [Heating and Cooling Equipment](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/heating-and-cooling-equipment.md) | IRC 2009 | 2 |

### The term in use

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

> A masonry heater is a heating appliance constructed of concrete or solid masonry, hereinafter referred to as masonry, which is designed to absorb and store heat from a solid-fuel fire built in the firebox by routing the exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox may include flow in a horizontal or …

— [IRC 2009 §RI002.1](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/chimneys-and-fireplaces.md)

> The firebox floor of a masonry heater shall be a minimum thickness of 4 inches (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation in accordance with Section 2113.2.

— [IBC 2009 §2112.3](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/masonry.md)


## The terms masonry heater 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 masonry heater covers:

- **[Solid Masonry](https://harth.build/resources/glossary/solid-masonry.md)** — IRC 2009: Load-bearing or nonload-bearing construction using masonry units where the net cross-sectional area of each unit in any plane parallel to the bearing surface is not less than 75 percent of its gross cross-sectional area.
- **[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.
- **[Chimney](https://harth.build/resources/glossary/chimney.md)** — IBC 2009: A primarily vertical enclosure containing one or more passageways for conveying flue gases to the outside atmosphere.
- **[Masonry](https://harth.build/resources/glossary/masonry.md)** — IBC 2009: A built-up construction or combination of building units or materials of clay, shale, concrete, glass, gypsum, stone or other approved units bonded together with or without mortar or grout or other accepted methods of joining.
- **[Solid](https://harth.build/resources/glossary/solid.md)** — IBC 2009: A material that has a melting point, decomposes or sublimes at a temperature greater than 68°F (20°C).

## Masonry Heater: 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 | |
| Re-check the requirement that uses it | Chimneys and Fireplaces (IRC 2009) | |
| Re-check the requirement that uses it | Masonry (IBC 2009) | |
| Re-check the requirement that uses it | Structural Tests and Special Inspections (IBC 2009) | |
| Re-check the requirement that uses it | Specific Appliances, Fireplaces and Solid Fuel-burning Equipment (IMC 2009) | |
| Confirm the dependent definition | Solid Masonry | |
| Confirm the dependent definition | Appliance | |
| Confirm the dependent definition | Chimney | |
| 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)
- [Solid Masonry: Building Code Definition](https://harth.build/resources/glossary/solid-masonry.md)
- [Appliance: Building Code Definition](https://harth.build/resources/glossary/appliance.md)
- [Masonry: Building Code Definition](https://harth.build/resources/glossary/masonry.md)
- [Chimney: Building Code Definition](https://harth.build/resources/glossary/chimney.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 masonry heater?

The International Residential Code (IRC) 2009 defines it in Definitions as: “A masonry heater is a solid fuel burning heating appliance constructed predominantly of concrete or solid masonry having a mass of at least 1,100 pounds (500 kg), excluding the chimney and foundation. It is designed to absorb and store a substantial portion of heat from a fire built in the firebox by routing exhaust gases through internal heat exchange channels in which the flow path downstream of the firebox includes at least one 180-degree (3.14-rad) change in flow direction before entering the chimney and which deliver heat by radiation through the masonry surface of the heater.” 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 masonry heater?

In this corpus the term is used across 6 chapters, led by Chimneys and Fireplaces 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 masonry heater?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Definitions: “A masonry heater is a solid fuel burning heating appliance constructed predominantly of concrete or solid masonry having a mass of at least 1,100 pounds (500 kg), excluding the chimney and foundation. It is designed to absorb and store a substantial portion of heat from a fire built in the firebox by routing exhaust gases …” It is defined in IRC 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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