Updated 2026-09-07

Building Code Glossary

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.

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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.

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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, 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 — 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 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	IMC 2009	3
Solar Systems	IMC 2009	2
Definitions	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 — IRC 2009: A system specifically addressed and regulated in this code and composed of components, devices, appliances and equipment.
Liquid — 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 — 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 and the ICC 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.

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 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.

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