You're not at the mercy of slick ads and sales pitches when you're shopping for a conventional storage tank water heater. Energy efficiency and performance specifications have been standardized in laboratory tests and virtually all water heaters can be evaluated and compared by the consumer in the market for a water heater replacement. A storage tank heater’s efficiency is expressed by its Energy Factor (EF) printed on the Department of Energy's yellow EnergyGuide label attached to every new heater. Information about the performance of a heater, expressed as its "First Hour Rating," is normally listed in the upper left-hand corner of the EnergyGuide label. Here's what's meant by those two parameters:
Energy Factor:This figure expresses a simple efficiency quotient: the amount of heat generated in ratio to the amount of energy consumed by a heater. In gas-fired conventional water heaters, some heat energy is lost in the combustion process. That energy literally goes up the vent with combustion gases as they are exhausted to the exterior of the home. The Energy Factor is further influenced by these variables:
Recovery efficiency: The efficiency of heat transfer from the source — the gas burner or the electric heating element — to the water.Standby loss: The amount of heat loss per hour, expressed as a percentage, from hot water in the storage tank.
Cycling loss: Heat loss occurring as water is circulated through the inlet pipe into the tank and then discharged through the outlet plumbing.
The higher the EF rating, the better. Standard efficiency gas water heaters usually have an average EF around .55 while high-efficiency units offer an average of .67 EF. Electric heaters offer higher EF ratings that range from .75 to .95. However, because the cost of electricity is an average of three times higher than gas in most parts of the country, operating costs of an electric water heater will usually be steeper than gas despite the higher EF. The newest advance in water heater technology — gas-fired condensing units that extract surplus heat from combustion gases before they are exhausted — offer an EF of .80 and above and are becoming more price-competitive all the time.
First Hour Rating. Getting the right size water heater replacement for your home means the last person in the bathroom isn't stuck with a cold shower. It means hot water's available for the dishwasher even though someone did a load of laundry not long ago. An accurate sizing calculation is based on the number of occupants in your home and the number of hot water outlets in order to figure the maximum amount of water your family will use in one hour during the time of daily highest demand. This figure is known as the "First Hour Rating" (FHR) and it's expressed in gallons. You'll want a heater with an FHR that is within a gallon or two of your estimated highest household demand.
Most water heater manufacturers incorporate FHR calculators on their websites that allow consumers to individually enter all hot water outlets in the house to arrive at a very precise First Hour Rating. However, you can use the following guidelines to get a rough idea of the capacity you'll need for standard houses in this range:
With one-and-a-half bathrooms, a First Hour Rating from 43 gallons for a one bedroom home up to 60 gallons for three bedrooms is required.With two or two-and-a-half bathrooms, a First Hour Rating from 60 gallons for a three-bedroom house up to 90 gallons for five bedrooms is required.With three or three-and-a-half bathrooms, a First Hour Rating from 72 gallons for a three-bedroom house up to 90 gallons for five bedrooms is required.