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Tankless Water Heaters, Advantage And Disadvantage You Should Know

Author : Tom Irvine


Tankless Water Heater, also called ondemand water heater, is a kind of hot water heater and is gaining in popularity. It instantly heats water as it flows through the device, and does not retain any water internally except for what is in the heat exchanger coil.

Tankless heaters are often installed throughout a household at more than one point-of-use, far from the central water heater, or larger models may still be used to provide all the hot water requirements for an entire house. The main advantages of tankless water heaters are a continuous flow of hot water and energy savings, as compared to a limited flow of continuously heating hot water from conventional tank water heaters.

How does tankless water heaters work? When there is a demand for hot water (e.g. a hot water tap is opened for a sink, shower, tub, or washing machine) the tankless water heater's water flow turbine senses the flow and starts the heating process. The water flow turbine sends a signal to the control board which looks at multiple factors: incoming water temperature, desired water temperature as set on the temperature controller, and the calculated difference between the two temperatures. Depending on the calculated incoming and desired water temperatures, the gas or electric flow into the burner assembly is modulated and the electronic ignition sequence begins. Water is heated to the desired temperature as it circulates through the copper heat exchanger providing continuous hot water. When the hot water tap is turned off, the tankless water heater shuts down and is placed in a standby mode pending the next call for hot water.

Combination or combi boilers, combines the central heating (CH) with (tankless) domestic hot water (DHW) in one box. They are not merely infinitely continuous water heaters having the ability to heat a hydronic heating system in a large house. When DHW is run off, the combi stops pumping water to the hydronic circuit and diverts all the boiler's power to instantly heating DHW. Some combis have small internal water storage vessels combining the energy of the stored water and the gas or oil burner to give faster DHW at the taps or increase the DHW flowrate.

Combi boilers are rated by the DHW flowrate. The kW ratings for domestic units are 24 kW to 54 kW, giving approximate flowrates of 9 to 23 litres per minute. There are larger commercial units available. High flowrate models will simultaneously supply two showers.

A further advantage is that more than one combi unit may be used to supply separate heating zones, giving greater time and temperature control, and multiple bathrooms. An example is one combi supplying the downstairs heating system and another the upstairs. One unit may supply one bathroom and one another. Having two units gives backup in case one combi is down, provided the 2 systems are connected with valves that are normally closed.

Installation cost is significantly lower and less space is required as water tanks and associated pipes and controls are not required.

Combination boilers have disadvantages. The water flow rate is likely to be less good than from a storage cylinder, particularly in winter. The power rating needs to be matched to heating requirements; heating water On Demand improves energy efficiency but limits the volume of water available at any moment. The water supply pressure must not be too low. A combination boiler has more moving parts that can break down, so can be less reliable than a tank system.


Author's Resource Box

Noritz America increases the technical level of the Water Heater industry by introducing advanced Tankless Hot Water Heaters and providing the education and support required by such progressive products.

Article Source:
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Tags:   Water Heaters, Tankless Water Heater, Tankless Heater, Hot Water Heaters, Tankless

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Submitted : 2011-04-19    Word Count : 699    Times Viewed: 343