by Bob Musgrave
(Atlanta, Georgia, USA)
Because of climate differences all over the world, cold countries need permanent water heating fixtures, while temperate countries need them only on certain times of the year. There are two kinds of water heaters, the tank type and the tankless water heaters.
Tankless water heaters, in turn, have two basic types as well – the ‘point of use’ and the ‘whole house’.
In contrast to traditional hot water heaters which use tanks for water storage, tankless water heaters work by directly heating the water needed on demand. Because they have no water tanks to store hot water, there is no standby heat loss.
What is called standby heat loss is the heat lost (and the energy wasted) by heating water and storing it in a tank, which eventually dissipates this heat. Once the system’s thermostat goes down (because the water cooled down), the machine is automatically turned on again to heat the water in anticipation of any future use.
This wasted energy is the basis for tankless water heater proponents to claim that their system is energy efficient.
Tankless Water Heater Types:
Both the ‘point of use’ and the ‘whole house’ type of tankless water heater work the same way. When cold water enters the unit, it is heated by a heating element (heat exchanger) which is turned on by a flow activated switch.
The heating element could be electric heating coils or a gas-fired burner using natural gas or propane. Usually, gas-fired units have more heating capacity and are used in larger, whole house units.
Sizing The Unit:
There are three considerations in sizing up the unit to buy: 1) the volume of water the unit is required to heat up, measured as flow rate in gallons per minute (GPM); 2) the temperature of the cold water entering the unit; and, 3) the desired temperature of the hot water coming from the unit.
These factors determine the type, the size and the number of units oftankless water heaters you need.
Point Of Use:
These units are relatively small. These are typically ‘dedicated use’ heaters serving one sink, faucet or shower head.
These are also less expensive than whole house units.
Whole house units have higher GM flow rate capacity. It can handle demands for more than one outlet at any one time (a faucet and a shower, a kitchen sink and a lavatory faucet, etc).
The size and number of whole house tankless water heaters you will need is determined by the number and types of fixtures you want running at the same time.
Click here to read more about energy efficient water heaters