# Heat Transfer Liquid: Building Code Definition > How the IMC 2009 define heat transfer liquid, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/heat-transfer-liquid/ - 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 | IMC 2009 (2009 editions transcribed in this corpus) | | Primary source | IMC 2009 Definitions (model text, not a jurisdiction's adopted text) | | Chapters using the term | 3 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Heat transfer liquid is a defined term in the International Mechanical Code (IMC) 2009, in Definitions. The code's own words are: “The operating or thermal storage liquid in a mechanical system, including water or other liquid base, and additives at the concentration present under” No other I-Code in this corpus defines it, so the IMC 2009 definition is the one to work from. The term is used in 3 chapters of this corpus, most often in Definitions (IMC 2009), Solar Systems (IMC 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. 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? **Heat Transfer Liquid** — IMC 2009, Definitions: > The operating or thermal storage liquid in a mechanical system, including water or other liquid base, and additives at the concentration present under ![Labeled code-term definition diagram: Heat Transfer Liquid: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/heat-transfer-liquid/diagram-1344.webp) *How the IMC 2009 define heat transfer liquid, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Heat Transfer Liquid** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/definitions.md) chapter of the International Mechanical Code (IMC) 2009: > The operating or thermal storage liquid in a mechanical system, including water or other liquid base, and additives at the concentration present under ## Where heat transfer liquid is used in the code The term appears in 3 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/imc-2009/definitions.md) | IMC 2009 | 3 | | [Solar Systems](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/solar-systems.md) | IMC 2009 | 2 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/definitions.md) | IRC 2009 | 1 | ## The terms heat transfer liquid 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 heat transfer liquid covers: - **[Mechanical System](https://harth.build/resources/glossary/mechanical-system.md)** — IRC 2009: A system specifically addressed and regulated in this code and composed of components, devices, appliances and equipment. - **[Liquid](https://harth.build/resources/glossary/liquid.md)** — IBC 2009: A material that has a melting point that is equal to or less than 68°F (20°C) and a boiling point that is greater than 68°F (20°C) at 14.7 pounds per square inch absolute (psia) (101 kPa). - **[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. ## Heat Transfer Liquid: 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 IMC | Definitions | | | Re-check the requirement that uses it | Definitions (IMC 2009) | | | Re-check the requirement that uses it | Solar Systems (IMC 2009) | | | Re-check the requirement that uses it | Definitions (IRC 2009) | | | Confirm the dependent definition | Mechanical System | | | Confirm the dependent definition | Liquid | | | 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) - [Mechanical System: Building Code Definition](https://harth.build/resources/glossary/mechanical-system.md) - [System: Building Code Definition](https://harth.build/resources/glossary/system.md) - [Liquid: Building Code Definition](https://harth.build/resources/glossary/liquid.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 heat transfer liquid? The International Mechanical Code (IMC) 2009 defines it in Definitions as: “The operating or thermal storage liquid in a mechanical system, including water or other liquid base, and additives at the concentration present under” 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 heat transfer liquid? In this corpus the term is used across 3 chapters, led by Definitions in the IMC 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. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Fheat-transfer-liquid%2F - View this page in a browser: https://harth.build/resources/glossary/heat-transfer-liquid/ - All resources for agents: https://harth.build/llms.txt