# Fixed-temperature heat detector plan symbol

Canonical URL: https://eloragrid.ai/symbols/iec-heat-detector-plan-symbol
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: HD
Drawing use: GA
Reference families: IEC

## Symbol convention

Convention: IEC
Form: Heat detector, fixed temperature
IEC 60617 installation-plan style (architectural and topographical installation symbols); independently drawn, not certified IEC geometry or a database identifier.

Fire alarm plan symbol for a fixed-temperature heat detector that alarms at a set temperature.

## In plain English

### What does Fixed-temperature heat detector plan mean?

Fixed-temperature heat detectors alarm when the surrounding air reaches a set point, commonly around 57 to 90 degrees Celsius depending on class. Plans draw the detector box with a temperature mark or the letter H, often with a class tag.

### A simple example

They are used where smoke detectors would false alarm, such as kitchens, plant rooms, car parks and dusty areas. The detection is slower than smoke, so coverage spacing is tighter and the reason for choosing heat should be clear. The symbol does not give the operating temperature or class. Check the schedule, especially in hot plant rooms.

### What the drawings help you do

Confirm the class suits the ambient temperature. Check spacing, which is tighter than for smoke. A rate-of-rise detector responds to a fast temperature increase; this one only to an absolute threshold.

### This particular reference

Fire alarm plan symbol for a fixed-temperature heat detector that alarms at a set temperature. A rate-of-rise detector responds to a fast temperature increase; this one only to an absolute threshold.

### Terms

- Rating: A value stating the conditions for which equipment is specified.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)
- [Electrical installation design methodology and references](https://www.electrical-installation.org/enwiki/General_rules_of_electrical_installation_design)


## What it represents

Fixed-temperature heat detectors alarm when the surrounding air reaches a set point, commonly around 57 to 90 degrees Celsius depending on class. Plans draw the detector box with a temperature mark or the letter H, often with a class tag.
They are used where smoke detectors would false alarm, such as kitchens, plant rooms, car parks and dusty areas. The detection is slower than smoke, so coverage spacing is tighter and the reason for choosing heat should be clear. The symbol does not give the operating temperature or class. Check the schedule, especially in hot plant rooms.

## How to read it

- Confirm the class suits the ambient temperature.
- Check spacing, which is tighter than for smoke.

## Information to show or reference

- State class or operating temperature.
- Tag loop and address.
- Note why heat detection is chosen.

## Important distinction

A rate-of-rise detector responds to a fast temperature increase; this one only to an absolute threshold.

## Facts

- Operating principle: Absolute temperature threshold
- Typical rooms: Kitchens, plant rooms, car parks
- Exact standard graphic: Not reproduced here; confirm the form against IEC 60617 and the project legend

## Public references

- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC graphical symbol context for installation plans; independently drawn here.
- [Electrical installation design methodology and references](https://www.electrical-installation.org/enwiki/General_rules_of_electrical_installation_design) — Schneider Electric — Electrical Installation Guide. Installation design context: life-safety systems are coordinated with the building electrical design.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.