Home water heaters -- currently under the scrutiny of the Consumer Product Safety Commission as it investigates scalding accidents and the Federal Trade Commission as it takes a look at home energy use -- are insulated storage tanks that supply hot water for washing and other uses. The water may be heated by any fuel -- gas, oil or electricity.

The capacity of a water heater is the amount of water the tank will hold and the time in which it will make more hot water. Storage capacities, when fired by gas, normally range from 30 gallons for apartments to 50 gallons for large houses.

Electric water heaters will have a much greater storage capacity because their recovery rate is low. Because of this low recovery rate, an 80-gallon electric heater is, in actual use, more like a 50-gallon gas heater.

Recovery rates of the three types of heater will vary. A typical gas water heater storing 40 gallons will recover more than 30 gallons of water that will rise 100 degrees in one hour. The better gas heaters will recover 100 percent of storage capacity in an hour, in which case storage capacity may be relatively small.

On the other hand, electric water heaters recover so slowly that you won't even find the recovery rate stamped on the name plate. There is no such thing as rapid recovery with electric water heaters; oil heaters have a very rapid recovery rate.

Here are estimates for the sizes of heaters various households need:

Thirty gallons for family of three.

Forty gallons for family of four.

Fifty gallons for family of five.

In view of the energy crisis, there might be some savings in utilizing a tank of with smaller storage capacity and more rapid recovery.

The widely used gas-fired heaters are cheap and efficient. However, they do require a flue for exhausting the gas -- as does a gas furnace. Gas heaters are now available with a flame of varying intensity that raises the temperature quickly, or maintains it during the night.

The variable flame minimizes the need for large storage capacity because the recovery is quicker.

Most electric water heaters have two 4500-watt heating elements within the tank that operate alternately -- never at the same time. The two heating elements evenly maintain and increase the heat recovery. The electric water heater is more expensive to operate, but a great advantage is that no flue is required.

Occasionally where there is no gas hookup available and the cost of electricity is high, an oil heater will be installed. This heater has extremely rapid recovery -- will over 100 percent of storage capacity in one hour. It is good for a large house or a hotel. It requires a flue, and the installation expense is higher than for gas or electric heaters.

A type of hot water supply commonly found with oil-fired boilers used for house heat is a system called summer-winter hookup. A coil, through which a separate water supply flows, is placed inside the boiler. When the hotwater tap is turned, water flows through the coil and is heated almost instantly.

Although the initial installation of one of these systems is less expensive than a gas or electric water heater, they are wasteful if used in the summer when no house heat is needed. In these days of energy shortage, use of these devices is definitely out. Other disadvantages include low storage capacity and an annoying drop in pressure when more than one spigot is turned on at a time.