Find Fact Sheets
Electric-Resistance Storage Water Heaters
Electric-resistance storage water heaters are the most common type of hot water heater used after fuel-fired heaters.
Submerged within the tank of water are one or two electric elements. The bottom portion of the tank maintains the minimum thermostat setting, while the upper portion is used as the demand increases. Electric-resistance systems are best used where the hot water use is small, electric rates are lower, or no other options exist. They generally involve higher operating costs.
Understanding the capacity of a water heater as it relates to your household hot water demand is crucial when purchasing a new system. Below are different types of electric resistance storage heater.
Quick Recovery Electric Resistance Storage Water Heater. The most common type, it typically consists of two 4,500-watt elements, one upper and one lower in a tank holding 50 to 66 gallons. The tank is usually made of steel lined with glass for corrosion protection.
Base-Loaded Electric Resistance Storage Water Heater. Contains one or two 500- to 3,000-watt elements and an 80- to 120-gallon tank. The greater storage volume paired with the lower wattage elements can be used to level the electrical load, shifting demand from utility peak load hours to off-peak hours.
Interruptible Electric Resistance Storage Water Heater. A storage water heater in which operation of the elements is remotely controlled, typically by radio or power line carrier signal, to disable element operation during utility peak loads. The system consists of two 4,500-watt elements and a 50- to 80-gallon tank. Interruption periods are typically less than four hours.
Point-Of-Use Electric Resistance Water Heater. This model is installed near the point where hot water is used. Due to the proximity of the heater and the location, the time required to get hot water is shortened. There is no need for a pumped recirculation loop and the associated heat loss is eliminated. Units usually include a one- to 20-gallon tank.
Electric-resistance heaters are efficient. The efficiency of the model is measured by the Energy Factor (EF), an indicator of how much fuel was used in relation to the amount of hot water actually produced and used from the tap on a typical day. This figure is based on:
Recovery Efficiency. How efficiently the heat from the energy source is transferred to the water.
Standby Losses. The percentage of heat loss per hour from the stored water compared to the heat content of the water (water heaters with storage tanks).
Cycling Losses. The loss of heat as the water circulates through a water heater tank, and/or inlet and outlet pipes.
When compared with highly efficient models of gas storage water heater, electric resistance heaters can be up to 30 % more efficient, with a minimum energy factor of .90. With a more efficient model, you waste less energy. High energy factors do not always result in lower annual operating costs. Operating cost is usually more dependent on the price of the selected fuel.
Insulation. Many high-efficiency systems contain a layer of foam, as high as R-19 insulation between the tank and the exterior of the water heater. In some cases, adding an insulating blanket to an older tank may increase efficiency. A blanket ranges from only $10-20.
Insulating your hot water pipes will reduce the energy losses from the tank to the faucet. Energy and water are wasted waiting for the hot water to reach the tap. Use plastic or rubber foam at least 1/2 inch thick to insulate the first 5 feet of hot and cold water pipe.
Lowering the Thermostat. Set the temperature to the lowest possible level that can provide your home with adequate hot water (generally 120°F or between the “low” and “medium” settings). Lowering the setting by 10°F results in 3-5% saving in energy costs. Thermostat dials can often read inaccurately. Be aware that multiple alterations may be needed to determine the right setting.
If you are away, turn the thermostat to either the lowest setting or turn the heater off.
Heat Traps. These devices can be installed to prevent unintended hot water flow out of the tank, and will save you from $15-$30 per month on your water heating bill. Specially designed fittings stop a convection current of hot water from escaping the tank. Traps are designed differently for use in either the hot or cold water line. Many new systems have such trapping devices already installed.
Electric-resistance heaters are less complex and safer to install than traditional fuel-fired heaters. They require no special venting, no air for combustion, and no gas lines. Some systems are designed with plastic, plastic-lined, or cement-lined tanks, which eliminate corrosion. Typically they last longer than fossil-fueled tanks and are safer and easier to maintain.
Electric water heaters can be located almost anywhere within a building without the need for combustion air and flues. This also makes them longer-lasting, easier to maintain and less subject to corrosion. They can be placed under counters and in cabinets, avoiding the use of floor space.
Unlike fuel-fired storage water heaters, electric resistance systems do not involve combustion as a significant part of the water-heating process and are less subject to corrosion. Electric units require less maintenance, which increases their longevity.
Hiring a qualified heating and plumbing contractor is suggested to ensure the proper installation of the system. In addition to the list of contractors on this site, you can find contractors through the Plumbing-Heating-Cooling Contractors-National Association (PHCC)
In terms of installation and cost of the system itself, electric-resistance heaters are similar to other conventional storage units. But in most cases, electricity costs approximately 3 times more per Btu than other fuels such as gas. Powered by the more expensive form of energy, electric-resistance systems can have high operating costs.
The Federal Trade Commission (FTC) requires that all electric storage water heaters be labeled with an "ENERGYguide" label. Based on the national average cost of electricity, this label compares the projected annual operating costs of various models and can aid you in your search for an appropriate system. Below is a cost analysis of two levels of electric resistance storage water heater efficiencies for consideration.
|Type||Energy Factor||Installed Cost||Yearly Energy Cost||Total Costs (13 years)|
|Minimum Efficiency Electric Storage||0.90||$750||$463||$6,769|
|High Efficiency Electric Storage||0.95||$820||$439||$6,528|
1. Purchase costs include our best estimates of installation labor and do not include financial incentives.
2. Operating cost based on hot water needs for typical family of four and energy costs of 9.5¢/kWh for electricity, $1.40/therm for gas, $2.40/gallon for oil.
3. Future operating costs are neither discounted nor adjusted for inflation.
Off Peak Metering. One way to reduce the high operating cost of electric water heaters is to take advantage of an off-peak or time of use tariff, if one is offered by your electric utility. Off peak metering usually involves hard wiring the electric water heater so that it will not draw power during peak times, usually summer afternoons. As the tank typically holds 40 or more gallons of hot water, you will be able to continue to use hot water during peak hours, and usually you will not notice any change. Off peak tariffs can provide a very significant savings, up to 50% of the monthly operating cost.
Manage My Projects
Why is this important?
Water heating is a principal energy cost in your household. Unlike traditionally fuel-fired tanks, electric resistance heaters only lose approximately 1% of energy per hour. With this low standby heat loss, they are extremely efficient.
Modern electric heaters are among the most popular types of systems, as they are easy to operate and maintain. Investing in a long-term, long-lasting system will allow you to conserve the natural resources you pay for by heating your water efficiently.