Building Code Glossary
Floor Furnace: Building Code Definition
How the IRC 2009, IMC 2009 define floor furnace, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · 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.
Direct answer
Floor furnace is a defined term in the International Residential Code (IRC) 2009, in Fuel Gas. The code's own words are: “A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such space.” The IMC 2009 carries the same definition word for word, so the term means the same thing in each. The term is used in 5 chapters of this corpus, most often in Fuel Gas (IRC 2009), Heating and Cooling Equipment (IRC 2009), Specific Appliances, Fireplaces and Solid Fuel-burning Equipment (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, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Floor Furnace — IRC 2009, Fuel Gas:
A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such space.
What must be verified before using this guidance?
Two of the I-Codes in this corpus define Floor Furnace, in identical words.
| Code | Where it is defined | Definition |
|---|---|---|
| IRC 2009 | Fuel Gas | A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such space. |
| IMC 2009 | Definitions | A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such space. |
Where floor furnace is used in the code
The term appears in 5 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 | IRC 2009 | 18 |
| Heating and Cooling Equipment | IRC 2009 | 18 |
| Specific Appliances, Fireplaces and Solid Fuel-burning Equipment | IMC 2009 | 10 |
| Definitions | IMC 2009 | 1 |
| Definitions | IRC 2009 | 1 |
The term in use
How the code actually writes about floor furnace, quoted from the 2009 text hosted here:
The lowest portion of the floor furnace shall have not less than a 6-inch (152 mm) clearance from the grade level;
An opening in the foundation not less than 18 inches by 24 inches (457 mm by 610 mm), or a trap door not less than 22 inches by 30 inches (559 mm by 762 mm) shall be provided for access to a floor furnace.
The terms floor furnace is built out of
The definition above leans on 3 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what floor furnace covers:
- Combustion — 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.
- Appliance — 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.
- Furnace — IRC 2009: A completely self-contained heating unit that is designed to supply heated air to spaces remote from or adjacent to the appliance location.
Floor Furnace: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IRC | Fuel Gas | |
| 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 | Heating and Cooling Equipment (IRC 2009) | |
| Re-check the requirement that uses it | Specific Appliances, Fireplaces and Solid Fuel-burning Equipment (IMC 2009) | |
| Re-check the requirement that uses it | Definitions (IMC 2009) | |
| Confirm the dependent definition | Combustion | |
| Confirm the dependent definition | Appliance | |
| Confirm the dependent definition | Furnace | |
| 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
- Combustion: Building Code Definition
- Appliance: Building Code Definition
- Furnace: Building Code Definition
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 publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of floor furnace?
The International Residential Code (IRC) 2009 defines it in Fuel Gas as: “A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such 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.
Which parts of the code depend on floor furnace?
In this corpus the term is used across 5 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 a floor furnace?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Fuel Gas: “A completely self-contained furnace suspended from the floor of the space being heated, taking air for combustion from outside such space and with means for observing flames and lighting the appliance from such space.” 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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