Thermal storage electric heaters charge with electricity during off-peak periods and release stored heat gradually, making their energy performance fundamentally different from direct-acting heaters. Energy consumption testing verifies charge efficiency, heat output, retention losses and standby power in accordance with IEC, EN and GB standards. This article explains the applicable standards, sample requirements, test items, methodologies and typical applications for storage heater energy performance evaluation.
Technical Overview
Thermal storage electric heaters, also known as storage heaters or heat-retention heaters, convert electrical energy into heat and store it within a high-density core material, typically magnesite or ceramic bricks, before releasing it into a room over an extended period. Because the charging, retention and discharge phases each involve energy losses, the true energy performance of these appliances cannot be assessed by nameplate power ratings alone. Energy consumption testing quantifies how effectively input electricity is converted into useful heat output, how much energy is retained during idle periods, and how much power is consumed in standby and control modes.
The principal references for this testing include IEC 60335-2-61 and EN 60335-2-61 for safety and functional performance of thermal-storage room heaters, IEC 60335-1 and its Chinese counterpart GB 4706.1 for general requirements, GB 4706.23 for particular requirements of indoor heaters, IEC 62301 and EN 50564 for standby power measurement, and Commission Regulation (EU) 2015/1188 for ecodesign requirements applicable to local space heaters sold in the European market. Accredited third-party laboratories conduct these evaluations under controlled thermal and electrical conditions to generate reproducible, standards-based results.
Testing Samples
Complete Storage Heater Units
Representative production models, including wall-mounted and floor-standing manual storage heaters as well as fan-assisted dynamic storage heaters, are submitted in new condition with all original charge regulators, discharge dampers, thermostats and electronic controls installed. Multiple units may be requested to account for manufacturing variation and to support repeat charge-discharge cycling.
Storage Core and Thermal Materials
Core material specimens, such as magnetite, magnesite or feolite-style ceramic bricks, may be sampled for thermal capacity, density and thermal conductivity characterization. These material parameters support the calculation of theoretical storage capacity and help interpret discrepancies between measured charge energy and delivered heat output.
Control Units and Sensing Components
Charge controllers, room and storage thermostats, input selectors, fans and associated sensors can be tested individually to evaluate control accuracy, hysteresis and auxiliary power draw, since controller behavior directly influences overall energy consumption profiles.
Testing Items
Energy consumption evaluation of storage heaters typically covers the following parameters:
- Nominal and measured input power during the charging phase
- Total charge energy consumption over a defined charging period
- Nominal heat output and delayed heat output during discharge
- Charge efficiency, expressed as stored energy divided by input energy
- Standing loss and heat retention performance during the retention period
- Discharge efficiency and useful heat delivered to the room
- Seasonal space heating energy efficiency in accordance with Regulation (EU) 2015/1188
- Standby and off-mode power consumption measured per IEC 62301 and EN 50564
- Auxiliary electricity consumption of fans, dampers and electronic controls
- Surface and core temperature rise profiles during charge and discharge
- Thermostat accuracy, hysteresis and control stability
- Verification of energy-related information declared in technical documentation and labeling
Testing Methods
Electrical Energy Measurement During Charging
The appliance is connected to calibrated power analyzers and energy meters that record voltage, current, active power and accumulated energy throughout the full charge cycle. Charging is performed from a stabilized supply at rated voltage and frequency, and the charge is terminated either by the appliance's own controller or after a defined duration, depending on the applicable standard. The recorded energy input establishes the baseline for all subsequent efficiency calculations.
Calorimetric Heat Output Measurement
Useful heat output is determined in a calibrated test enclosure or climatic chamber maintained at reference ambient temperature. Heat released during the discharge and retention phases is measured either by calorimetric methods, using the thermal balance of the test room, or by heat flux instrumentation on the appliance surfaces. Continuous data logging integrates heat delivery over time, yielding total useful energy output for comparison against charge energy input.
Charge, Retention and Discharge Cycle Testing
The appliance undergoes complete operational cycles consisting of a charging phase, a retention phase simulating overnight idle conditions, and a controlled discharge phase. Core and surface temperatures are monitored with thermocouples at multiple locations, while energy input and output are simultaneously recorded. Repeated cycles verify consistency, reveal heat soaking behavior and quantify retention losses characteristic of the storage core insulation system.
Standby and Auxiliary Power Testing
Power consumption in standby, off-mode and networked standby states is measured using the low-power measurement procedures of IEC 62301 and EN 50564. Fan and damper auxiliary consumption during discharge is recorded separately, as these values feed directly into the seasonal efficiency calculation required by ecodesign regulations.
Efficiency Calculation and Reporting
Measured input energy, useful heat output, standing losses and auxiliary consumption are combined to compute overall efficiency and seasonal space heating energy efficiency. Results are compared against declared values and applicable minimum requirements, and a comprehensive test report documents test conditions, instrumentation, raw data and conclusions.
Applications
Energy consumption test reports for storage heaters serve multiple purposes across the product lifecycle:
- Regulatory compliance demonstration for market access in regions requiring ecodesign or energy performance conformity, including CE marking support under Regulation (EU) 2015/1188
- Verification of declared energy values supporting energy labeling obligations under Regulation (EU) 2015/1186
- Manufacturer research and development, including comparison of core materials, insulation systems and control strategies
- Factory production control and periodic batch verification to maintain consistency across manufacturing runs
- Qualification of appliances for off-peak tariff programs, where verified charge timing and retention performance are essential
- Procurement evaluation by utilities, housing authorities and facility managers seeking documented energy performance data
- Technical documentation support for importers, distributors and retailers fulfilling due diligence obligations
FAQ
Which standards are most relevant to storage heater energy testing?
IEC 60335-2-61 and EN 60335-2-61 address thermal-storage room heaters specifically, while GB 4706.1 and GB 4706.23 apply to the Chinese market. IEC 62301 and EN 50564 cover standby power measurement, and Regulation (EU) 2015/1188 defines ecodesign efficiency requirements for the European market.
How is the energy efficiency of a storage heater determined?
Efficiency is derived by comparing measured useful heat output during discharge with total electrical energy input during charging, then accounting for standing losses and auxiliary consumption. The result is expressed as overall efficiency and, where required, as seasonal space heating energy efficiency per the applicable ecodesign methodology.
What samples and quantities are typically required?
Testing generally requires one to three complete production units in new condition, along with documentation such as rating labels, wiring diagrams and control specifications. Additional core material specimens may be requested when material characterization is included in the scope.
How long does a typical test program take?
A single charge-retention-discharge cycle spans roughly 24 to 48 hours, and most programs require multiple cycles plus conditioning. Depending on scope, full energy performance evaluation typically takes from one to several weeks, including instrumentation setup and reporting.
Why is standby power measured separately for storage heaters?
Modern storage heaters incorporate electronic charge controllers, sensors and communication modules that draw power continuously even when no heating is delivered. Because this background consumption affects annual energy totals, regulations mandate its separate measurement and inclusion in efficiency declarations.