Heat Detectors and Fire Alarm Systems — BS 5839-6, Grade D Alarms, and Interconnectable Smoke and Heat Detectors for UK Electricians

Every electrician fitting a kitchen, completing an EICR, or first-fixing a new build needs to understand fire detection. The regulations are specific: smoke alarms are not suitable for kitchens, CO alarms are mandatory on floors with solid fuel appliances, and landlords in England must fit alarms on every storey. Getting it wrong means failing an inspection or, worse, a system that doesn't protect occupants.

This guide covers BS 5839-6 grades and categories, when to use heat detectors instead of smoke alarms, mains vs battery options, RF interconnection, and the products that meet current standards.

BS 5839-6: Grades and Categories

BS 5839-6:2019 is the UK standard for domestic fire detection. It uses two classifications:

Grade — the type of power supply

• Grade A: Fully addressable panel-based system (commercial / large residential)
• Grade C: Mains-powered with central control unit
• Grade D: Mains-powered with integral battery backup — the standard for most new builds and landlord-grade installations
• Grade E: Mains-powered without backup (older standard, not recommended for new installations)
• Grade F: Battery-only — acceptable for lowest-risk situations and retrofit where mains wiring is impractical

In practice: New builds require Grade D. Private landlords in England (Smoke and CO Alarm Regulations 2022) must fit alarms "in working order" — Grade D is best practice, Grade F is compliant but requires battery maintenance.

Category — which rooms are covered

• LD3: Escape routes only (hallways, landings) — minimum requirement
• LD2: Escape routes plus rooms where fire is most likely to start (kitchen, lounge)
• LD1: All rooms including bedrooms — maximum protection

For landlords: LD3 per storey is the minimum legal requirement. For new builds under Part B Building Regulations, LD2 is typically required. Recommend LD2 as a minimum for all residential work.

Heat Detectors vs Smoke Alarms — Where Each Type Belongs

Smoke alarms (both ionisation and optical) are inappropriate for kitchens and garages where cooking fumes, steam, and vehicle exhaust cause nuisance false alarms. Heat detectors solve this:

Note: Do not fit CO alarms instead of heat detectors in kitchens — they detect different hazards. CO alarms are mandatory where solid fuel appliances are present on that floor, but they do not replace fire detection.

Heat Detector Types

Rate-of-Rise (Class A1R)

Triggers when temperature rises rapidly (typically more than 8°C per minute) OR when fixed temperature reaches 58°C. Provides faster response in fast-flaming fires. The Class A1R designation means it meets both rate-of-rise and fixed-temperature criteria under EN 54-5. Most professional-grade products are A1R.

Fixed Temperature Only (Class A2S)

Triggers only at fixed threshold (usually 58°C or 90°C). Slower response but fewer nuisance trips in environments with ambient heat fluctuations. The 90°C variant suits commercial kitchens or plant rooms.

Standard domestic installation: Class A1R, 58°C threshold, interconnectable.

Wired vs RF Interconnection

Interconnection means all detectors sound simultaneously when one triggers — essential for LD2/LD1 systems and required for Grade D installations with multiple heads.

Wired interconnection

A dedicated interconnect cable (typically 1.5mm² twin with earth) links all detectors on a ring or spur. Standard for new build first-fix where the wiring can be installed before boarding out. Up to 12 detectors on a single interlink circuit. Reliable, no battery dependency on the RF link.

RF wireless interconnection

Radio-frequency interconnect allows retrofit without chasing walls. Detectors communicate wirelessly when one triggers. Suitable for rental properties, conversions, and extensions where running new cable is impractical. Verify that all heads in the system use the same RF protocol — cross-brand RF interconnection is not guaranteed.

Grade D detectors require mains power (230V, usually a spur from the lighting circuit) with battery backup for continued operation during power failures.

Mains Wiring for Grade D Detectors

Grade D mains detectors are typically wired on a dedicated spur from the nearest lighting circuit or consumer unit. Standard approach:

• 1.0mm² or 1.5mm² T&E cable from the lighting circuit, or a dedicated circuit from the consumer unit
• Junction box spur, or looped at the ceiling rose (where space permits)
• Earth the metal backplate if present
• Interconnect wire (L, N, E + switched-live interconnect) if wired interconnection is used
• Battery backup built into each head — no additional wiring required

Part P compliance: Adding or modifying a mains fire alarm circuit in a dwelling is notifiable work in England and Wales under the Building Regulations. This must be certified by a registered competent person scheme (NICEIC, NAPIT, or ELECSA) or notified to Building Control. Battery-only (Grade F) installation is not notifiable.

Landlord Obligations — England

The Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022 (in force from 1 October 2022) require private landlords in England to:

• Fit at least one smoke alarm on every storey of the property used as living accommodation
• Fit a CO alarm in any room with a gas boiler, gas fire, oil boiler, or solid fuel appliance
• Test alarms at the start of each tenancy and ensure they are in working order
• Repair or replace alarms promptly when a tenant reports a fault

Scotland has had mandatory smoke alarm requirements since 2022 (Housing (Scotland) Act 2014): LD1 standard, interlinked, with heat detector in kitchen. Wales follows similar requirements from 2022. Northern Ireland regulations differ — check with DCAN.

Product Selection: APM Electricals Fire Detection Range

All four products below are stocked and available for immediate despatch from apmi.uk.

1. Hispec Heat Detector Lithium Battery RF Interconnectable

Hispec Heat Detector Lithium Battery RF Interconnectable

Grade F battery-powered heat detector with 10-year sealed lithium cell and RF wireless interconnect. Class A1R, 58°C fixed temperature. Ideal for kitchen retrofit where mains wiring is impractical. RF interconnect compatible with Hispec RF range (smoke, CO, and heat). No cable chasing required — fix, sync, done.

Best for: Landlord retrofit, kitchen addition to existing RF system, temporary accommodation.

2. Apollo AlarmSense Heat Detector (A1R)

Apollo 55000-190APO AlarmSense Heat Detector (A1R)

Commercial-grade Class A1R heat detector from Apollo, a leading UK fire detection manufacturer. Part of the AlarmSense range which supports two-wire conventional panel systems (Grade A/C). Suitable for installation into a panel-based system in HMOs, houses converted to flats, and commercial kitchens. Rate-of-rise plus 58°C fixed. Base sold separately — check Apollo AlarmSense base compatibility.

Best for: Panel-based systems, HMOs, flats with central fire panel.

3. Axiom Mains Heat Detector Alarm — 230V, 58°C, Interlinkable

Axiom Mains Heat Detector Alarm 230V 58°C

Grade D mains-powered heat detector with wired interconnect and built-in sounder. 230V, 58°C Class A1R. Interlinkable via the standard switched-live interconnect line — compatible with most wired smoke/heat detector brands. Includes tamper-proof locking connector. Standard 150mm backplate. Suitable for new build and rewire kitchen installations where mains cable is already routed to the ceiling.

Best for: New build, full rewire, wired Grade D system in kitchen.

4. Axiom ALRFHM Mains Heat Alarm with Battery Backup RF Interconnectable

Axiom ALRFHM Mains Heat Alarm with Battery Backup RF

Grade D mains heat detector with both battery backup and RF wireless interconnect — the ideal upgrade option for properties that have mains to the ceiling but where routing an interconnect cable would require additional work. RF interconnect means any alarm in the system triggers all heads simultaneously without additional wiring. Class A1R, 58°C. 9V backup battery (included).

Best for: Extensions, refurbishments, converting Grade F systems to mains, mixed wired/RF systems.

Quick Selection Guide

Installation Tips

• Position: Centre of the ceiling where possible. No closer than 300mm from a wall. No closer than 600mm from any cooking appliance or extract fan to reduce nuisance trips.
• Height: Heat rises — ceiling mounting gives fastest response. Do not mount on walls unless ceiling mounting is genuinely impractical.
• Test after fitting: Use the test button, not real heat (hair dryer testing can cause damage). RF systems require pairing — follow manufacturer's sync procedure.
• Battery maintenance: Grade F units with sealed 10-year lithium cells require replacement of the whole unit at end of life. Mark the installation date on the unit. Grade D units require periodic battery check — include this in EICR follow-up notes.
• Record keeping: Note the location, type (Grade, Class), and installation date on the completion certificate. For rental properties, provide the landlord a test record.

Shop Fire Detection at APM Electricals

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APM Electricals
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Phone: 020 8702 8080
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