Electric resistance heaters are 100% efficient, but the relatively high cost of utility energy usually makes electricity a poor choice for space heating. Electric thermal storage (ETS) heaters are one way of getting around that problem. They draw energy during off-peak hours when supply is plentiful and rates are relatively low. An ETS system contains electric heating elements within dense ceramic bricks, which store heat.
ETS heaters are available as stand-alone room heaters, much like a wood heater, but also as whole-house forced-air or hydronic systems. They can be incorporated into an existing heating system as a backup for an electric furnace or to supplement a heat pump, but also work as a principal source of heat.
Local electricity rates and rate structures are a key consideration in purchasing an ETS heater, since these units use a lot of electricity. Room-size heaters draw 1.32 to 10.8 kW, with outputs from 46,602 to 136,480 Btu. The smallest Steffes central-air heater draws 14 kW. An ETS heater may require wiring upgrades to handle the current. The run-time for the units depends on the size of the heater, the size of the heated space, the heating load, and how much stored energy was used during the previous heating cycle.
Off-peak rates, which are lower than during high-usage times, are usually available at night or on weekends—when utility system demand is the lowest. Take, for example, the residential rate structure offered by Portland (Oregon) General Electric. Its on-peak rate is $0.1327 per kWh, its mid-peak rate is $0.075 per kWh, and the off-peak rate is $0.0442 per kWh—one-third of the peak rate. The biggest advantage for the utility is the avoided cost of not having to build new power plants to meet spikes in demand during peak hours.
ETS heaters probably can’t beat natural gas at current fuel prices, but they can save money for consumers who currently use propane or No. 2 fuel oil. The ability of these appliances to balance the load on the grid by storing energy is a key advantage, says Paul Steffes, CEO of Steffes Corp. a manufacturer of ETS systems.
An electric thermal storage unit. Note that the side insulation has been rolled back to reveal the ceramic bricks inside the unit.