The present invention relates to hot water heaters, and relates more particularly to such a hot water heater which has heat exchanging devices connected in series to recycle heat energy for pre-heating water permitting water to be quickly heated to the desired temperature.
Conventional hot water heaters commonly comprise a single heat exchanging device to carry water, and a gas burner to heat the flat bottom of the heat exchanging device. During the operation of a hot water heater, hot air from the heat exchanging device is directly drawn away from the housing of the hot water heater into the air, causing the air polluted. Because cold water is not pre-heated before it is guided into the heat exchanging device, it takes a lot of time and consumes a lot of energy to heat water to the desired temperature. Furthermore, when the heat source is operated to heat the heat exchanging device, heat is transmitted to water from the bottom, therefore heat cannot be evenly distributed through the inside of the hot water heater. Because different parts of the hot water heater bear different temperatures, their structural strength will be differently affected, causing the service life of the hot water heater shortened.