What cable size do I need for a storage heater?

Most storage heaters (1.7kW-3.4kW) need 2.5mm² cable on a 16A or 20A circuit. A 3.4kW heater draws about 14.8A, so 16A minimum. For older properties with long cable runs, consider 4mm² to reduce voltage drop. Each heater typically needs its own circuit.

Do storage heaters need their own circuit?

Generally yes - storage heaters draw high current continuously for 7+ hours overnight. Sharing circuits risks overloading and nuisance tripping. Each heater should have a dedicated radial circuit from the consumer unit, controlled by the off-peak supply.

Can I put two storage heaters on one circuit?

Only if the combined load is within the circuit rating. Two 1.7kW heaters (7.4A each = 14.8A total) could share a 20A circuit. But two 3.4kW heaters (14.8A each = 29.6A) cannot. Separate circuits are usually safer and more flexible.

What about panel heaters - same cable requirements?

Panel heaters are typically lower wattage (400W-1.5kW) and can often share circuits. A 20A circuit could supply several panel heaters totalling up to 4kW. They don't usually need Economy 7 as they heat on demand, not overnight storage.

How does Economy 7 wiring work?

The electricity meter has two rates - peak and off-peak. Storage heater circuits connect through a time switch or dedicated off-peak supply that only provides power during cheap-rate hours. The meter tracks usage separately for billing purposes.

Is Economy 7 still worth it?

It depends on your usage pattern. Off-peak rates are cheaper, but peak rates are higher than standard tariffs. If you use lots of electricity during the day, you may pay more overall. Modern alternatives like heat pumps are often more cost-effective.

Can I replace storage heaters with panel heaters?

Yes, but panel heaters run on peak-rate electricity, so running costs may be higher. They're simpler to install and more controllable. Consider the whole-house heating cost before switching. The existing wiring can usually be reused.

What size consumer unit for storage heater system?

Each storage heater needs one way. A 4-bedroom house might have 5-6 storage heaters plus immersion heater. Allow 8-10 ways for heating plus normal circuits. Some systems use a separate consumer unit just for heating circuits.

Do I need RCD protection for storage heaters?

BS 7671 requires RCD protection for most circuits. Storage heater circuits should have 30mA RCD protection, either via RCBO or shared RCD. This is especially important as heaters often have accessible elements.

How do I know if my supply can handle storage heaters?

Add up all heater wattages plus other high loads (shower, cooker, immersion). If total exceeds 60A (14kW) on single phase, you may need supply upgrade. Most houses have 80A-100A supplies which handle typical storage heater installations.

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Electric Storage Heater Cable Sizing Calculator

Calculate the correct cable size for storage heaters, panel heaters, and electric heating circuits

Storage Heater Cable Quick Facts

Storage heaters typically 1.7kW to 3.4kW each
Each heater usually needs dedicated radial circuit
Economy 7/10 meters require off-peak wiring
Panel heaters can often share circuits (lower wattage)
Consider total heating load when sizing main supply

Cable Size Calculator

BS 7671:2018+A2:2022 compliant

1. Load Current

1kW ≈ 4.35A at 230V

2. Cable Length (meters)

3. Installation Method

Lighting circuit (3% voltage drop limit)

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Common Storage Heater Installations

Single storage heater (2kW)

13A circuit minimum, 2.5mm² cable usually sufficient

Large storage heater (3.4kW)

16A or 20A circuit, 2.5mm² cable for most runs

Multiple storage heaters (whole house)

Dedicated circuit per heater, check total supply capacity

Panel heaters (400W-1.5kW)

Can share 20A radial with multiple heaters on same circuit

Economy 7 system

Off-peak supply wiring, separate consumer unit or time switch

Related Heating & High-Load Circuits

Storage heaters often combine with immersion heaters on Economy 7 systems. For modern alternatives, see our air source heat pump calculator. Supplementary heating? Check electric underfloor heating for bathrooms and kitchens.

Storage Heater Cable Sizing

Storage heater cable sizing calculates the conductor size needed to safely supply electric storage heaters. These heaters charge overnight on cheap off-peak electricity (Economy 7/10) and release heat during the day. Each heater typically needs its own circuit due to continuous high current draw during the charging period.

Storage Heater Installation Costs (2024)

Typical UK installation costs including cable, circuit work, and labour.

Installation Scenario	Materials	Labour	Total
Single storage heater circuit	£60-120	£120-200	£180-320
Replace storage heater wiring	£80-150	£150-250	£230-400
Full house storage heater install (4-6 units)	£400-700	£600-1000	£1000-1700
Economy 7 meter + wiring setup	£150-300	£200-400	£350-700
Panel heater circuit (multiple heaters)	£100-180	£150-280	£250-460

Prices as of 2024. Does not include cost of storage heater units.

Economy 7 and Off-Peak Tariffs

Economy 7 provides 7 hours of cheaper electricity overnight (typically 12am-7am) for storage heater charging. The meter has two registers - peak and off-peak. Wiring must ensure storage heaters only draw power during off-peak hours via time switches or dedicated off-peak circuits from a dual-rate meter.

Storage Heater Ratings

Storage heaters are sized by heat output and storage capacity. Common ratings: 1.7kW (small rooms), 2.5kW (medium rooms), 3.4kW (large rooms/lounges). The kW rating indicates charging power draw - a 3.4kW heater draws 14.8A continuously for 7 hours overnight. Size heaters to room heat loss calculations.

Dual-Rate Metering

Dual-rate meters record electricity use at two different prices. Off-peak hours (typically 7 hours overnight) are charged at a lower rate for storage heater charging. Modern smart meters can provide similar functionality. Check with your supplier about off-peak tariff availability and timing.

Frequently Asked Questions

Related Electrical Calculators

Immersion Heater

Economy 7 hot water

Underfloor Heating

Electric UFH circuits

Heat Pump

Modern heating alternative

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