# Atmospheric Pressure: Building Code Definition > How the IRC 2009 define atmospheric pressure, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/atmospheric-pressure/ - 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 | 14 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Atmospheric pressure is a defined term in the International Residential Code (IRC) 2009, in Fuel Gas. The code's own words are: “The pressure of the weight of air and water vapor on the surface of the earth, approximately 14.7 pounds per square inch (psia) (101 kPa absolute) at sea level.” 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 14 chapters of this corpus, most often in Definitions (IPC 2009), Fuel Gas (IRC 2009), Fire and Smoke Protection Features (IBC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted. Record the jurisdiction, the adopted edition, the application date and any local amendment that rewrites the definition before you use it on a live project, because a term redefined by amendment changes every requirement that depends on it. *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? **Atmospheric Pressure** — IRC 2009, Fuel Gas: > The pressure of the weight of air and water vapor on the surface of the earth, approximately 14.7 pounds per square inch (psia) (101 kPa absolute) at sea level. ![Labeled code-term definition diagram: Atmospheric Pressure: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/atmospheric-pressure/diagram-1344.webp) *How the IRC 2009 define atmospheric pressure, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Atmospheric Pressure** 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 pressure of the weight of air and water vapor on the surface of the earth, approximately 14.7 pounds per square inch (psia) (101 kPa absolute) at sea level. ## Where atmospheric pressure is used in the code The term appears in 14 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/definitions.md) | IPC 2009 | 4 | | [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 3 | | [Fire and Smoke Protection Features](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) | IBC 2009 | 2 | | [Industrial Ovens](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/industrial-ovens.md) | IFC 2009 | 2 | | [Vents](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/vents.md) | IPC 2009 | 2 | | [Water Supply and Distribution](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) | IPC 2009 | 2 | | [Solar Systems](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/solar-systems.md) | IRC 2009 | 2 | | [Vents](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/vents.md) | IRC 2009 | 2 | | [Water Supply and Distribution](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/water-supply-and-distribution.md) | IRC 2009 | 2 | | [Use and Occupancy Classification](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/use-and-occupancy-classification.md) | IBC 2009 | 1 | | [Hazardous Materials-general Provisions](https://harth.build/resources/building-codes/us-states/rhode-island/ifc-2009/hazardous-materials-general-provisions.md) | IFC 2009 | 1 | | [Boilers, Water Heaters and Pressure Vessels](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/boilers-water-heaters-and-pressure-vessels.md) | IMC 2009 | 1 | _2 further chapters mention the term._ ### The term in use How the code actually writes about atmospheric pressure, quoted from the 2009 text hosted here: > The pressure in the furnace shall be maintained as nearly equal to the atmospheric pressure as possible. — [IBC 2009 §715.4.2](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/fire-and-smoke-protection-features.md) > The relief pipe shall be sized to relieve air pressure inside the ejector to atmospheric pressure, but shall not be less than 1¼ inches (32 mm) in size. — [IPC 2009 §916.5.2](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/vents.md) > These devices shall operate under normal atmospheric pressure when the critical level is installed at the required height. — [IPC 2009 §608.13.6](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) ## Atmospheric Pressure: 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 | Definitions (IPC 2009) | | | Re-check the requirement that uses it | Fuel Gas (IRC 2009) | | | Re-check the requirement that uses it | Fire and Smoke Protection Features (IBC 2009) | | | Re-check the requirement that uses it | Industrial Ovens (IFC 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) - [Code Official: Building Code Definition](https://harth.build/resources/glossary/code-official.md) - [Code: Building Code Definition](https://harth.build/resources/glossary/code.md) - [Fuel Gas: Building Code Definition](https://harth.build/resources/glossary/fuel-gas.md) - [Vent: Building Code Definition](https://harth.build/resources/glossary/vent.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 atmospheric pressure? The International Residential Code (IRC) 2009 defines it in Fuel Gas as: “The pressure of the weight of air and water vapor on the surface of the earth, approximately 14.7 pounds per square inch (psia) (101 kPa absolute) at sea level.” 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 atmospheric pressure? In this corpus the term is used across 14 chapters, led by Definitions in the IPC 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 standard atmospheric pressure? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Fuel Gas: “The pressure of the weight of air and water vapor on the surface of the earth, approximately 14.7 pounds per square inch (psia) (101 kPa absolute) at sea level.” 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fatmospheric-pressure%2F - View this page in a browser: https://harth.build/resources/glossary/atmospheric-pressure/ - All resources for agents: https://harth.build/llms.txt