# Thermostat: Building Code Definition

> How the IECC 2009 define thermostat, where the wording differs, and which chapters depend on the term.

- Canonical: https://harth.build/resources/glossary/thermostat/
- 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 | IECC 2009 (2009 editions transcribed in this corpus) |
| Primary source | IECC 2009 Definitions (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

Thermostat is a defined term in the International Energy Conservation Code (IECC) 2009, in Definitions. The code's own words are: “An automatic control device used to maintain temperature at a fixed or adjustable set point.” No other I-Code in this corpus defines it, so the IECC 2009 definition is the one to work from. The term is used in 14 chapters of this corpus, most often in Commercial Energy Efficiency (IECC 2009), Fuel Gas (IRC 2009), Residential Energy Efficiency (IECC 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?

**Thermostat** — IECC 2009, Definitions:

> An automatic control device used to maintain temperature at a fixed or adjustable set point.

![Labeled code-term definition diagram: Thermostat: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/thermostat/diagram-1344.webp)

*How the IECC 2009 define thermostat, where the wording differs, and which chapters depend on the term.*

## What must be verified before using this guidance?

**Thermostat** is defined once in this corpus, in the [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) chapter of the International Energy Conservation Code (IECC) 2009:

> An automatic control device used to maintain temperature at a fixed or adjustable set point.

## Where thermostat 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 |
| --- | --- | --- |
| [Commercial Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/commercial-energy-efficiency.md) | IECC 2009 | 41 |
| [Fuel Gas](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md) | IRC 2009 | 15 |
| [Residential Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/residential-energy-efficiency.md) | IECC 2009 | 13 |
| [Energy Efficiency](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/energy-efficiency.md) | IRC 2009 | 13 |
| [Fixtures, Faucets and Fixture Fittings](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/fixtures-faucets-and-fixture-fittings.md) | IPC 2009 | 6 |
| [Water Supply and Distribution](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-supply-and-distribution.md) | IPC 2009 | 5 |
| [Plumbing Fixtures](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/plumbing-fixtures.md) | IRC 2009 | 5 |
| [Specific Appliances, Fireplaces and Solid Fuel-burning Equipment](https://harth.build/resources/building-codes/us-states/new-hampshire/imc-2009/specific-appliances-fireplaces-and-solid-fuel-burning-equipment.md) | IMC 2009 | 3 |
| [Elevators and Conveying Systems](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/elevators-and-conveying-systems.md) | IBC 2009 | 2 |
| [Special Fuel-burning Equipment](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/special-fuel-burning-equipment.md) | IRC 2009 | 2 |
| [Definitions](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/definitions.md) | IECC 2009 | 1 |
| [Water Heaters](https://harth.build/resources/building-codes/us-states/new-hampshire/ipc-2009/water-heaters.md) | IPC 2009 | 1 |

_2 further chapters mention the term._

### The term in use

How the code actually writes about thermostat, quoted from the 2009 text hosted here:

> This section applies to buildings served by unitary or packaged HVAC equipment listed in Tables 503.2.3 (1) through 503.2.3(5), each serving one zone and controlled by a single thermostat in the zone served.

— [IECC 2009 §503.3](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/commercial-energy-efficiency.md)

> Sauna heaters shall be equipped with a thermostat which will limit room temperature to 194°F (90°C).

— [IRC 2009 §G2440.6](https://harth.build/resources/building-codes/us-states/maryland/irc-2009/fuel-gas.md)

> At least one thermostat shall be provided for each separate heating and cooling system.

— [IECC 2009 §403.1](https://harth.build/resources/building-codes/us-states/maryland/iecc-2009/residential-energy-efficiency.md)


## The terms thermostat 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 thermostat covers:

- **[Automatic](https://harth.build/resources/glossary/automatic.md)** — IBC 2009: As applied to fire protection devices, a device or system providing an emergency function without the necessity for human intervention and activated as a result of a predetermined temperature rise, rate of temperature rise or combustion products.
- **[Control](https://harth.build/resources/glossary/control.md)** — IRC 2009: A manual or automatic device designed to regulate the gas, air, water or electrical supply to, or operation of, a mechanical system.
- **[Device](https://harth.build/resources/glossary/device.md)** — IRC 2009: Aunit of an electrical system that carries or controls electrical energy as it principal function.

## Thermostat: 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 IECC | Definitions | |
| Re-check the requirement that uses it | Commercial Energy Efficiency (IECC 2009) | |
| Re-check the requirement that uses it | Fuel Gas (IRC 2009) | |
| Re-check the requirement that uses it | Residential Energy Efficiency (IECC 2009) | |
| Re-check the requirement that uses it | Energy Efficiency (IRC 2009) | |
| Confirm the dependent definition | Automatic | |
| Confirm the dependent definition | Control | |
| Confirm the dependent definition | Device | |
| 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)
- [Automatic: Building Code Definition](https://harth.build/resources/glossary/automatic.md)
- [Control: Building Code Definition](https://harth.build/resources/glossary/control.md)
- [Device: Building Code Definition](https://harth.build/resources/glossary/device.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 thermostat?

The International Energy Conservation Code (IECC) 2009 defines it in Definitions as: “An automatic control device used to maintain temperature at a fixed or adjustable set point.” 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 thermostat?

In this corpus the term is used across 14 chapters, led by Commercial Energy Efficiency in the IECC 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 the definition of a thermostat?

In the 2009 I-Codes hosted here it is a defined term rather than a description. The IECC 2009 states, in Definitions: “An automatic control device used to maintain temperature at a fixed or adjustable set point.” It is defined in IECC 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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