Quick-Recovery Heaters
This class of heater, as the name implies, has the ability to produce hot water at a more rapid rate than the slow-recovery type. It is frequently employed where repeated heavy requirement for hot water makes it essential to have a sufficient amount of water available on demand.
Thermostats used are of the throttling or snap-action type. Primarily the throttling thermostat is the one in which the amount of gas valve opening is directly proportional to the tem- perature changes of water in the tank. In the snap-action thermo- stat, the change from a completely open to a completely closed position of the valve, or vice versa, is accomplished by a snap action produced by a clicker diaphragm motivated by the temperature in the tank.
The essential difference between the slow- and quick-recovery heater lies in the amount of gas consumed by each unit. Thus, for example, a quick-recovery heater with a 25,000-Btu input will deliver 25 gallons of hot water per hour indefinitely, whereas a slow-recovery heater can never burn more than a certain relatively low and known amount of gas with an accompanying reduction in hot-water delivery.
Slow-Recovery Heaters
The gas-fired slow-recovery water heater is designed to keep a supply of hot water in the storage tank and, by means of a constantly burning gas flame, deliver hot water continuously to this tank.
Thermostats employed can be of the graduating or snap-action type. With the graduating thermostat, the burner operates between a low and high flame—the low position of the flame serving as a pilot to keep the heater lighted and serving as a source of standby heat.
The slow-recovery automatic water heater is very economical since it can never burn more than a certain amount of gas, depend- ing on the regulation offered by the thermostat. Also, the small amount of heating surface keeps the standby loss at a minimum, making this type of heater very advantageous where economy is the primary consideration.