Point-of-use Water Heaters | My Business | Mississippi Power | A Southern Company

Point-of-use Water Heaters

Where individual hot water loads are isolated, a point-of-use water heater may be used instead of a central source system. Point-of-use systems avoid the long piping runs and the related cost and heat loss associated with central hot water systems and distributed points of use. Point-of-use water heater systems consist of multiple instantaneous water heaters and small-volume storage water heaters located at or near the location where hot water is needed.

Point-of-use water heater applications provide hot water at or near the location where it is needed. They operate without the heat loss of central hot water systems with long piping runs and recirculation loops. The short distance between the water heater and the point of use means that hot water is available almost immediately, without wasting water and waiting for heated water to flow from the central system.

Applications

  • In general, low-volume uses of hot water in isolated or remote locations in a building.
  • For hot water loads which require prompt delivery of hot water to the fixtures.
  • In buildings where central water heating system would be very expensive or difficult to install.
  • In place of recirculation loops.

Possible applications

  • Remote bathrooms.
  • Hotels and motels.

Efficiency

Storage water heaters

Electric storage water heaters are inherently more efficient than gas units. While typical gas water heaters are limited by a combustion and heat transfer efficiency of about 77% or less (higher for pulse-combustion and condensing water heaters), electric water heaters have their elements immersed in the tank, so that the conversion efficiency is close to100%. Gas water heater tanks also have greater heat loss because of the open flue through the center of the tank.

Because they are well-insulted, heat loss from the tank is low and air temperature has little effect on the operation and performance of electric water heaters.

Instantaneous water heaters

The volume of hot water delivered by an instantaneous water heater is limited by the electrical input capacity of the heater and the circuit serving the heater and the incoming cold water temperature. Useful capacity declines somewhat during winter when the incoming water temperature is low. The following table illustrates the maximum temperature increase provided by typical instantaneous water heaters. Cold water inlet temperatures are below 35°F during winter in many locations, indicating that such heaters are inadequate to meet many hot water loads.

Typical
Voltage
Input
(kW)
Temperature Increase (°F)
    0.5
gpm
0.75
gpm
1.0
gpm
1.5
gpm
2.0
gpm
110 3 41 27 20 14 10
208/220 4.5 61 41 31 20 15
208/220 7 95 64 48 32 24
240 9.5 123 82 61 41 31