Electric Panel Heaters and Fan Heaters: Selection, Wiring, and Installation for UK Electricians

Electric panel heaters and fan heaters are the go-to solution for supplementary heating in bathrooms, hallways, loft conversions, and any space where extending the wet central heating system is impractical or uneconomical. They require no pipework, no boiler capacity, and no pressurised system — just a dedicated circuit and correct thermostat wiring.

This guide covers heater selection by application, circuit design to BS 7671, wiring configurations, thermostat types, IP rating requirements for bathroom zones, and the common installation pitfalls that generate callbacks.

Types of Electric Heater

Panel Heaters (Radiant/Convector)

Panel heaters use a resistive element to warm a metal panel, which then heats the room by a combination of radiant heat and convection. They are slim (typically 80–120 mm deep), wall-mounted, and available from 400 W to 2,500 W. Most modern panel heaters feature integral electronic thermostats with 24/7 programmers and open-window detection.

Key features to compare:

• Element type — dry stone (quick heat-up), fluid-filled (slower but more even), ceramic (high thermal mass)
• Thermostat accuracy — ±0.5°C for precision models vs ±1–2°C for basic units
• Wi-Fi control — useful for holiday lets and rental properties
• Lot 20 compliance — required for new installations under the Energy-related Products Regulation 2021 (EcoDesign)

Lot 20 (EcoDesign) requires all electric local space heaters sold in the UK/EU after January 2018 to include an electronic thermostat, open window detection, and a 24/7 timer as a minimum. Ensure products you specify are Lot 20 compliant — non-compliant units cannot legally be sold new.

Fan Heaters

Fan heaters circulate air across a heating element, delivering rapid warm-up times. They are suited to infrequently used rooms (garages, utility rooms, porches) where the fast response outweighs the higher noise level. IP-rated fan heaters (IP21 or IP24) are available for bathrooms and en suites outside Zone 1.

Fan heaters draw high current at start-up. A 2 kW fan heater will draw approximately 8.7 A at 230 V — size the circuit accordingly and ensure the RCBO/MCB is rated to handle inrush current without nuisance tripping.

Infrared Radiant Heaters

Far-infrared (FIR) panel heaters warm objects and surfaces rather than air — useful in draughty or open spaces (garages, workshops, outdoor covered areas) where convective heat is lost quickly. They require a line-of-sight to the occupant to be effective and are not suitable as primary heating for enclosed rooms.

Sizing and Selection

Wattage Calculation

The standard rule of thumb for a well-insulated UK property is 100 W per m² of floor area. For older or poorly insulated properties, increase to 150 W/m². For bathrooms with tiled walls and floors (high thermal mass, rapid heat loss), use 150–200 W/m².

Room size	Good insulation	Average insulation	Poor insulation
8 m² (small bathroom)	800 W	1,200 W	1,500 W
12 m² (bedroom)	1,200 W	1,800 W	2,000 W
20 m² (living room)	2,000 W	3,000 W	4,000 W
30 m² (open plan)	3,000 W	4,500 W	6,000 W

For rooms above 2,500 W requirement, consider multiple heaters on separate circuits rather than a single large unit — this also provides redundancy and avoids overloading a single circuit.

Bathroom Zone Requirements

BS 7671 (18th Edition) Section 701 defines four zones in bathrooms and shower rooms:

• Zone 0 — inside the bath or shower tray. No electric heaters permitted.
• Zone 1 — above the bath/shower to 2.25 m from finished floor level. Minimum IP44 required. No panel heaters permitted (fan heaters with suitable IP rating only if floor-standing and not fixed).
• Zone 2 — 0.6 m horizontally from Zone 1 boundary or zone 1 in older editions. Minimum IP44 required. Panel heaters and fan heaters with IP44+ are acceptable.
• Outside zones — standard IP20 equipment acceptable, but IPX4 (splash-proof) recommended for all bathroom-adjacent installations as good practice.

Note: BS 7671:2018+A2:2022 removed the former Zone 2 and 3 distinction in some interpretations. Check the current edition of GN 7 (Guidance Note 7 — Special Locations) for up-to-date zone boundaries. When in doubt, specify IP44 throughout the bathroom.

Circuit Design

Dedicated Circuit Requirement

All fixed electric heaters above 3 kW should have a dedicated circuit from the consumer unit. Heaters below 3 kW may be connected via a fused connection unit (FCU) from a ring main in non-bathroom locations, but a dedicated radial circuit is best practice and simplifies fault-finding.

For bathrooms, Section 701 requires that socket outlets are not permitted within 3 m of a bath or shower door, so panel heaters in bathrooms must be fixed and wired via a dedicated circuit with a double-pole (DP) isolator outside the zones, or via an FCU located outside the bathroom.

Cable Sizing

Use cable sizing tables (Article #90) to determine correct cable size. For typical panel heater circuits:

• Up to 1,500 W (6.5 A): 1.0 mm² T&E in conduit or 1.5 mm² clipped direct
• 1,500–2,500 W (6.5–11 A): 1.5 mm² T&E clipped direct, 2.5 mm² in thermal insulation
• 2,500–3,600 W (11–16 A): 2.5 mm² T&E clipped direct
• 3,600–5,000 W (16–22 A): 4.0 mm² T&E

Where cable runs through thermal insulation (loft insulation, wall cavity insulation boards), apply the appropriate derating factor from BS 7671 Appendix 4. This can reduce current-carrying capacity by 50% or more for cable fully surrounded by insulation.

RCBO/MCB Selection

Protect electric heater circuits with a Type B RCBO (30 mA RCD + MCB in one device). Type B is correct for resistive loads — fan heaters with motors may benefit from Type C to tolerate inrush current. An RCBO provides both overload/short-circuit protection and earth fault protection in a single device, simplifying consumer unit allocation.

Size the MCB at 110% of full-load current as a minimum. For a 2 kW heater at 230 V: I = P/V = 2000/230 = 8.7 A → use a 10 A MCB. For a 3 kW heater: 13 A → use a 16 A MCB.

Wiring Configurations

Direct-Wired with Integral Thermostat

Most modern panel heaters have an integral electronic thermostat and need only a permanent live (L), neutral (N), and earth (E) connection. The thermostat switches the element load internally. This is the simplest installation — no external thermostat or contactor required.

Wiring at the heater: Brown (L) → terminal L, Blue (N) → terminal N, Green/Yellow (E) → earth terminal. Use a 20 A DP isolator adjacent to the heater (or just outside the bathroom) to allow safe isolation for servicing.

External Thermostat and Heater

For installations requiring a wall-mounted room thermostat (separate from the heater), the thermostat is wired into the live feed to switch the heater on/off. The thermostat must be rated for the full load current of the heater — most wall-stat thermostats are rated 16 A (3,600 W at 230 V).

Consumer Unit → RCBO → DP Isolator → Thermostat → Heater (L, N, E)
                                    → Permanent N direct to Heater N

Where the heater also has an integral thermostat, the external thermostat provides zone control (e.g. a programmable room thermostat), while the integral thermostat provides fine temperature control and safety cutout. Both thermostats work in series — if either is off, the heater is off.

Contactor-Controlled (Multiple Heaters)

For multiple heaters in a large open-plan space or across multiple rooms on a single zone, use a contactor (typically 25 A or 40 A) controlled by a low-voltage thermostat signal (5 V or 24 V) from a zone controller. This keeps thermostat wiring at low voltage (safer, smaller cable) while the contactor handles the full heater load.

Thermostat Types

Bimetallic (Mechanical) Thermostats

The simplest type — a bimetallic strip bends with temperature change and makes/breaks the circuit. Accuracy typically ±2–3°C with significant hysteresis. Still found in cheap panel heaters and convectors. Not Lot 20 compliant for new installations.

Electronic (NTC/PTC Thermistors)

More accurate (±0.5–1°C), faster response, no hysteresis. Standard in modern Lot 20-compliant heaters. Can be combined with digital display, 7-day programmers, and adaptive start (heater starts earlier to hit target temperature by programmed time).

Wi-Fi Smart Thermostats

Allow remote control via smartphone app. Useful for holiday lets, second homes, and landlord portfolios. Require 2.4 GHz Wi-Fi signal at heater location. Check that the thermostat supports the load — some smart stat modules are low-voltage relay types and require a separate high-current relay or contactor for heaters above 3 kW.

For zoned control of multiple panel heaters across a property, consider UFH thermostat systems (see Article #132: UFH Thermostats and Controls) which provide multi-zone programmable control suitable for electric heaters as well as UFH.

Installation Best Practice

Mounting Height

Panel heaters work by convection — mount at low level (bottom of heater 150–300 mm from finished floor) for maximum convective circulation. Do not mount directly on skirting boards unless specifically designed for skirting-board mounting (there are dedicated skirting heater products). Ensure 50 mm clearance minimum from the floor surface for airflow.

Cable Entry

Most panel heaters have bottom cable entry. Use appropriate cable glands and ensure the cable is supported within 300 mm of the heater cable entry point. Where conduit is used, terminate the conduit into the heater back box with a conduit gland — this maintains IP rating and mechanical protection.

Furniture Clearance

Maintain minimum clearance from furniture, curtains, and combustible materials as specified by the manufacturer — typically 150 mm above and 50 mm each side. Mark clearance requirements clearly for the client on handover. Failure to observe clearances is a common cause of overheating and fire risk.

Thermal Cutout Testing

On commissioning, verify the overheat cutout operates by blocking airflow for the manufacturer's specified test duration (typically 5 minutes). The heater should shut down safely. Do not do this without confirming the test procedure with the manufacturer — some overheat cutouts are non-resettable and will void warranty if triggered during testing.

Part P and Certification

Fixed electric heater installations in dwellings are notifiable work under the Building Regulations Part P (England) and equivalent regulations in Wales, Scotland (Building (Scotland) Regulations 2004), and Northern Ireland. As a registered electrician under a competent person scheme (NICEIC, NAPIT, ELECSA), you self-certify and issue the relevant Building Regulations compliance certificate (Building Regulations Compliance Certificate in England and Wales). Homeowners undertaking DIY installations must notify their local authority Building Control before starting work.

For bathroom installations (Special Location under Section 701), the work is always notifiable regardless of scope. Issue a completed Minor Electrical Installation Works Certificate (MEIWC) or an Electrical Installation Certificate (EIC) for complete new circuits, as appropriate to the scope.

Common Faults and Callbacks

Heater Not Reaching Temperature

Check: thermostat setting vs room temperature, open-window detection triggered (common in draughty rooms), heater undersized for room (recalculate W/m²), cable undersized causing voltage drop, or control circuit fault (external thermostat not calling).

MCB/RCBO Tripping

Resistive heaters don't normally trip RCDs unless there's an earth fault. If a 30 mA RCBO trips repeatedly, check for earth leakage in the heater element (megger test the element with heater disconnected). Fan heaters have motors which can develop earth faults in humid conditions. Replace the element or heater if insulation resistance is below 0.5 MΩ (to BS 7671 minimum during installation — in practice, below 1 MΩ warrants investigation).

Thermostat Hunting

If the heater cycles rapidly (on/off every few seconds), the thermostat deadband is too narrow or the heater is oversized. Check thermostat settings. Some electronic thermostats allow hysteresis adjustment. If not, replace with a thermostat with a wider deadband or downsize the heater.

Further Reading

• Article #17: Fused Connection Units — for heaters wired via FCU from ring main
• Article #24: Consumer Unit Replacement — dedicated circuit protection for heater circuits
• Article #26: UK Electrical Cable Types — T&E, heat-resistant cable for heater wiring
• Article #53: RCDs and RCBOs — protection device selection
• Article #90: Cable Sizing — correct cable selection for heater circuits
• Article #118: Electric Storage Heaters — storage heaters for off-peak tariffs
• Article #132: UFH Thermostats — programmable zone controls suitable for panel heaters
• Article #74: Electric Trace Heating — pipe frost protection circuits
• Article #85: Electric Shower Installation — bathroom zone wiring and Part P compliance

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