A heat detector triggers on temperature rather than smoke, so it belongs wherever smoke detection would false-alarm constantly — kitchens, serveries, plant rooms, laundries, garages. Choose rate-of-rise (A1R) for spaces at normal ambient, and fixed temperature (Class B) where it is already hot and variable.
This article covers commercial detection certified to EN54-5, on systems designed to BS 5839-1. For houses and flats, see our guide to interlinked smoke alarms instead — that is a different standard and a different product.
1. Why fit heat rather than smoke
Smoke detectors are more sensitive to a real fire earlier. That is not in dispute, and where you can use one, you should.
The problem is that a smoke detector cannot distinguish smoke from anything else that scatters light or ionises: steam from a dishwasher, fumes from a grill, dust from a workshop, exhaust from a car in a garage. Put one in a commercial kitchen and it will go off during service — and a system that cries wolf gets isolated by staff, which leaves the building with no detection at all.
A heat detector ignores all of that. It is less sensitive by design, and in those rooms that is precisely the point: a detector that actually works beats a better detector that has been taped over.
Trade Tip: If someone tells you a smoke detector “keeps going off for no reason”, do not change the detector for the same type and hope. Ask what happens in that room at the time it triggers. Nine times out of ten it is steam, aerosol or dust, and the correct answer is a heat detector or a multi-sensor — not a more expensive smoke head.
2. Rate-of-rise (A1R) versus fixed temperature (Class B)
Both are heat detectors. They decide differently.
Rate-of-rise, class A1R — watches how fast the temperature climbs. A rapid rise triggers it even before an absolute threshold is reached, so it responds faster to a genuine fire. It suits rooms that normally sit at ordinary ambient temperature.
The C-TEC C4403A1R is an ActiV A1R rate-of-rise heat detector certified to EN54-5, running 9–33 V. This is the default choice for most heat-detected rooms.
Fixed temperature, class B — waits for an absolute threshold and ignores the rate entirely. That matters where the ambient temperature swings hard and fast in normal use: directly over a commercial cooking line, in a boiler room, in a laundry. A rate-of-rise head in those places can be tripped by ordinary operation.
The C-TEC C4403B is the fixed-temperature sibling, 75 °C Class B.
Trade Tip: The rule of thumb we use at the counter: if the room gets hot fast as part of doing its job, go fixed temperature. If it should stay at room temperature, go rate-of-rise. A kitchen ceiling away from the cooking line is usually A1R; directly above the range is usually Class B.
3. Multi-sensors, where the argument won't settle
Some rooms genuinely sit on the fence — an open-plan space with a kitchenette, a break room, a servery hatch. Rather than pick wrong, a multi-sensor combines both technologies in one head and uses the combination to distinguish a real fire from a kettle.
The Nittan EV-PH is an addressable multi-sensor pairing optical smoke with a 54 °C A1R heat element, on the Nittan Evolution FSK protocol.
4. The protocol trap — carries straight over from panels
This is the mistake that stops a device working, and detectors are where it bites hardest because they all look the same.
An addressable detector only talks to a panel running its protocol. Two white ceiling heads of identical size and shape can be entirely incompatible:
- C-TEC CA-series (such as the CA402 programmable heat detector) speak CAST.
- Nittan EV-series (such as the EV-PH) speak Nittan Evolution FSK.
- Other panels in the same family run Apollo XP95/Discovery or Hochiki ESP.
None of these are interchangeable. Read the protocol off the panel before ordering — our guide to commercial fire alarm systems sets out which panel takes which family.
5. Siting, and the ceiling void nobody checks
Heat rises and spreads across the ceiling, so a heat detector goes on the ceiling, away from the edges. Two practical points:
- Coverage per head is smaller than for smoke. Heat travels less far before dissipating, so you generally need more heat detectors than you would smoke detectors to cover the same room. Do not assume a like-for-like swap keeps the same spacing.
- Watch for anything that blocks the flow of hot air — deep beams, bulkheads, high shelving. Heat will pool on the wrong side of an obstruction and the detector will not see it.
Spacing, coverage and category are design decisions under BS 5839-1, and they are competent-person work. We supply the detectors and check protocol compatibility; the layout and the commissioning certificate come from a fire alarm engineer.
Summary: choosing a heat detector
| Situation | Choose |
|---|---|
| Room at normal ambient, steam or dust present | Rate-of-rise A1R |
| Directly over cooking, boiler room, laundry | Fixed temperature, 75 °C Class B |
| Open-plan with a kitchenette, break room | Multi-sensor (optical + A1R heat) |
| Clean office, corridor, escape route | Smoke detection, not heat |
| Any addressable system | Match the panel protocol — CAST, Nittan FSK, Apollo or Hochiki |
| Spacing and category | BS 5839-1 design by a competent person |
Expert Help in the West Midlands
Villa Road, Birmingham, since 1975. We hold heat detectors, multi-sensors, call points and sounders across the C-TEC and Nittan ranges. Bring a photograph of the panel label and we will confirm the protocol before you buy — that one check prevents the most expensive mistake in fire alarm ordering.
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Frequently asked questions
What is the difference between a heat detector and a smoke detector?
A smoke detector senses combustion products and responds earlier to most fires. A heat detector senses temperature and ignores steam, dust and fumes, which makes it the right choice in kitchens and plant rooms where a smoke head would false-alarm.
Should I use rate-of-rise or fixed temperature?
Rate-of-rise (A1R) for rooms that normally sit at ordinary ambient temperature. Fixed temperature (Class B, typically 75 °C) where the space gets hot quickly as part of normal operation, such as directly above a cooking line.
Can I fit any heat detector to my fire alarm panel?
No. On an addressable system the detector must match the panel's protocol — CAST, Nittan Evolution FSK, Apollo XP95/Discovery or Hochiki ESP. Identical-looking detectors from different families will not work.