Heat Detector Temperature Chart — Classes & Color Codes
The heat detector temperature classifications, per NFPA 72 Table 17.6.2.1 (2022 edition): the rating range in °F and °C, the maximum ceiling temperature each class may be used at, and the color code marked on the device. Match the class to the space's highest normal ambient — the maximum-ceiling column — not to the rating range.
Heat detector temperature classification
| Classification | Rating (°F) | Rating (°C) | Max ceiling (°F) | Color code |
|---|---|---|---|---|
| Low | 100–134 | 39–57 | 80 | None (uncolored) |
| Ordinary | 135–174 | 58–79 | 100 | None (uncolored) |
| Intermediate | 175–249 | 80–121 | 150 | White |
| High | 250–324 | 122–162 | 225 | Blue |
| Extra High | 325–399 | 163–204 | 300 | Red |
| Very Extra High | 400–499 | 205–259 | 375 | Green |
| Ultra High | 500–575 | 260–302 | 475 | Orange |
Rating range vs. maximum ceiling temperature
The two temperature columns do different jobs. The rating range is the temperature at which the detector actually alarms. The maximum ceiling temperature is the hottest the space is allowed to get normally with that class installed — always well below the rating, so ordinary temperature swings never cause a false alarm. You select a detector by the maximum-ceiling column: find the class whose ceiling limit clears the space's highest normal ambient, and the rating range takes care of itself.
That is why a kitchen, boiler room, or unconditioned attic gets an Intermediate or High detector rather than an Ordinary one — not because you want it to alarm at a higher temperature, but because the space normally runs hot enough that an Ordinary detector would nuisance-trip.
The color codes — and the one everyone misses
From Intermediate up, each class is color-marked so an inspector can read the rating at a glance: white for Intermediate, blue for High, red for Extra High, green for Very Extra High, and orange for Ultra High. The catch is the bottom two: both Low and Ordinary detectors are uncolored. Assuming Ordinary has a color — or reading an uncolored detector as something other than Low/Ordinary — is a common mistake on inspection.
Common questions
What temperature does an ordinary heat detector activate at?
An Ordinary-classification heat detector is rated 135–174°F (NFPA 72 Table 17.6.2.1, 2022 edition) and may be used where the maximum ceiling temperature stays at or below 100°F. It is the standard choice for normal occupied spaces. Where the ambient runs hotter — a boiler room or an attic — you step up to an Intermediate detector (175–249°F), used up to a 150°F ceiling.
What are the heat detector color codes?
Low and Ordinary detectors carry no color mark. From Intermediate up, the code is white (Intermediate), blue (High), red (Extra High), green (Very Extra High), and orange (Ultra High). A frequent field error is thinking Ordinary is a color — it is uncolored, and so is Low.
How do I pick a heat detector temperature rating?
Choose the classification whose maximum ceiling temperature is above the highest ambient the space normally reaches, with margin. The rating range sits well above that ceiling so normal temperature swings never trip the detector — an Ordinary detector rated 135–174°F is only allowed where the ceiling stays under 100°F, leaving room before it would activate.
Run your whole job on the same numbers
These NORDIX tools are a taste of the full platform — bid pipeline, estimating, and job costing that carry your numbers from the first bid to the final invoice.
See what NORDIX does →