Water Heaters - Energy Usage

The average household uses around 3500 kilowatt-hours of electricity or 230 therms of natural gas to heat water annually. Water heating consumes approximately 15% of the electricity and 25% of the natural gas used in residences. Water heating is the MOST variable class of energy consumption among families and varies according to water-heater capacity, climate, economic status, work schedule and age.

Water heaters use energy in 3 ways: demand, standby and distribution. Demand means energy is used for heating incoming cold water up to the temperature set point as hot water in the tank is used. Demand energy depends on water heater efficiency, occupant behavior, and consumption of fixtures like shower, clothes washer and dishwasher.

Standby energy accounts for heat lost through the storage tank's walls. Standby losses amount to 20% to 60% of the total water-heating energy. Households using less hot water have a higher percent of standby losses. Distribution losses consist of heat escaping through the pipes and fixtures. Pipes near the water heater lose heat even when water isn't flowing because hot water rises out of the tank, cools off in the nearby pipes, then falls back down into the tank.

Americans us 15-40 gallons of hot water per day per person. Water heating systems are designed for recovery capacities of 3-20 gallons per hour per resident. Most single-family homes have 40-gallon or 50-gallon storage tanks.

You can see that the "little old water-heater" is crucial to everyday living - and energy usage.

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