Gas units can heat a full 75-gallon tank in one hour. Electric units take as long as three to four hours to heat a full tank. New model water heaters convert about 75 percent of their energy into heat, up 10 points in the past five years. Blow says it is not necessary for homeowners to wrap heaters with insulation, a dangerous practice if insulation restricts airflow to the heater. Manufacturers now use at least 1 inch of foam insulation inside the heater to keep water hot.
Efficiency is more than insulation.
Heat traps prevent buoyant hot water from escaping out the top into pipes. And until recently, water heaters cycled water up to 18 times a day to keep water a constant temperature. Newer models cut cycle rates in half. Blow says typical water heater capacity has risen from 30 gallons to 75 gallons. The reason is the surge in popularity of whirlpool tubs and larger homes with more bathrooms.