# Relief Valve, Vacuum: Building Code Definition > How the IRC 2009 define relief valve, vacuum, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/relief-valve-vacuum/ - 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 | 6 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Relief valve, vacuum is a defined term in the International Residential Code (IRC) 2009, in Fuel Gas. The code's own words are: “A valve that automatically opens and closes a vent for relieving a vacuum within the hot water supply system, depending on whether the vacuum is above or below a predetermined value.” 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 Water Heaters (IPC 2009), Water Supply and Distribution (IPC 2009), Solar Systems (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](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? **Relief Valve, Vacuum** — IRC 2009, Fuel Gas: > A valve that automatically opens and closes a vent for relieving a vacuum within the hot water supply system, depending on whether the vacuum is above or below a predetermined value. ![Labeled code-term definition diagram: Relief Valve, Vacuum: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/relief-valve-vacuum/diagram-1344.webp) *How the IRC 2009 define relief valve, vacuum, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Relief Valve, Vacuum** 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: > A valve that automatically opens and closes a vent for relieving a vacuum within the hot water supply system, depending on whether the vacuum is above or below a predetermined value. ## Where relief valve, vacuum 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 | | --- | --- | --- | | [Water Heaters](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-heaters.md) | IPC 2009 | 4 | | [Water Supply and Distribution](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) | IPC 2009 | 4 | | [Solar Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/solar-systems.md) | IMC 2009 | 2 | | [Water Heaters](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/water-heaters.md) | IRC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 | | [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 1 | ### The term in use How the code actually writes about relief valve, vacuum, quoted from the 2009 text hosted here: > An approvedmeans, such as a cold water" dip" tube with a hole at the top or a vacuum relief valve installed in the cold water supply line above the top of the heater or tank, shall be provided to prevent siphoning of any storage water heater or tank. — [IPC 2009 §504.1](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-heaters.md) > All water pressure tanks shall be provided with a vacuum relief valve at the top of the tank that will operate up to a maximum water pressure of 200 psi (1380 kPa) and up to a maximum temperature of 200°F (93°C). — [IPC 2009 §606.5.9](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) > Bottom fed tank-type water heaters and bottom fed tanks connected to water heaters shall have a vacuum relief valve installed that complies with ANSI Z21.22. — [IRC 2009 §P2803.7](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/water-heaters.md) ## Relief Valve, Vacuum compared with Relief Valve, Pressure These two are the closest pair in the 2009 I-Codes: about 52 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 | | --- | --- | | **Relief Valve, Vacuum** (IRC 2009) | automatically, relieving, vacuum, within, hot, water, supply, system | | [Relief Valve, Pressure](https://harth.build/resources/glossary/relief-valve-pressure.md) (IRC 2009) | automatic, relief, pressure | 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 relief valve, vacuum and relief valve, pressure. ## The terms relief valve, vacuum 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 relief valve, vacuum covers: - **[Water Supply System](https://harth.build/resources/glossary/water-supply-system.md)** — IPC 2009: The water service pipe, water distribution pipes, and the necessary connecting pipes, fittings, control valves and all appurtenances in or adjacent to the structure or premises. - **[Hot Water](https://harth.build/resources/glossary/hot-water.md)** — IRC 2009: Water at a temperature greater than or equal to 110° P (43°C). - **[System](https://harth.build/resources/glossary/system.md)** — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping. - **[Vacuum](https://harth.build/resources/glossary/vacuum.md)** — IPC 2009: Any pressure less than that exerted by the atmosphere. - **[Valve](https://harth.build/resources/glossary/valve.md)** — IRC 2009: A device used in piping to control the gas supply to any section of a system of piping or to an appliance. ## Relief Valve, Vacuum: 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 | Water Heaters (IPC 2009) | | | Re-check the requirement that uses it | Water Supply and Distribution (IPC 2009) | | | Re-check the requirement that uses it | Solar Systems (IMC 2009) | | | Re-check the requirement that uses it | Water Heaters (IRC 2009) | | | Confirm the dependent definition | Water Supply System | | | Confirm the dependent definition | Hot Water | | | Confirm the dependent definition | System | | | 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) - [Water Supply System: Building Code Definition](https://harth.build/resources/glossary/water-supply-system.md) - [Hot Water: Building Code Definition](https://harth.build/resources/glossary/hot-water.md) - [Vacuum: Building Code Definition](https://harth.build/resources/glossary/vacuum.md) - [System: Building Code Definition](https://harth.build/resources/glossary/system.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 relief valve, vacuum? The International Residential Code (IRC) 2009 defines it in Fuel Gas as: “A valve that automatically opens and closes a vent for relieving a vacuum within the hot water supply system, depending on whether the vacuum is above or below a predetermined value.” 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 relief valve, vacuum? In this corpus the term is used across 6 chapters, led by Water Heaters 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 a vacuum relief valve? In the 2009 I-Codes hosted here it is a defined term rather than a description. The IRC 2009 states, in Fuel Gas: “A valve that automatically opens and closes a vent for relieving a vacuum within the hot water supply system, depending on whether the vacuum is above or below a predetermined value.” 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%2Frelief-valve-vacuum%2F - View this page in a browser: https://harth.build/resources/glossary/relief-valve-vacuum/ - All resources for agents: https://harth.build/llms.txt