Manual Water Heaters
Manual water heaters, also referred to as circulating tank or side arm heaters, are of the conventional design with the gas burner and accompanying heating coils mounted on the side of the hot-water storage tank as shown in Figure 4-63.
Manual water heaters are generally equipped with copper coils 161⁄2 to 20 feet in length and with either 3⁄4 – or 1-inch outside diameter. The coils are usually made of copper tubing of No. 20 Stubbs gauge. Other designs are occasionally employed—for example, the internal or underfired units intended to overcome liming in hard- water areas.
These heaters usually have between 20,000 and 30,000 Btu capacity, although the maximum sizes run up to 85,000 Btu capacity. The
smallest-size manual heater will deliver about 19 gallons of hot water per hour. This size heater is generally ample for most homes in which the conventional 30-gallon tank is used for storing the hot water.
The manual water heater was formerly widely employed because of its comparatively low cost and economy in operation. As the name implies, manual water heaters are nonautomatic and supply hot water quickly by turning on and lighting the gas shortly before the warm water is required. Automatic water heaters have largely replaced the manual type because the former require little or no attention when in operation.