A direct system delivers hot water that is heated instantly, just before it comes out of the tap.
An indirect system pre heats the water and holds it in an insulated tank.
An indirect system is best!
As the water is heated as part of the central heating system.
Where you have a number of people, all of whom may wish to use hot water at the same time. ie; A family of more than one.
As it will deliver hot water to many taps and applications at the same time.
A direct system uses more fuel to heat the water, as it has to raise the temperature of the water from below 12C to perhaps 30C in an instant.
If you have more than one tap and there is more than one person, then you need to know where that other person is and what they are doing before you turn any tap on.
If you turn on a hot tap, they may be having a shower and run out of hot water, and become upset, when their hot water disappears.
If you turn on a cold tap, they may get burnt.
If you have low water pressure there may not be any hot water (or cold water) at peak times.
People buy direct systems because they are cheap and easy to fit.
direct cold water advantages:-
1) cheaper to install 2) drinking water available from all draw off points 3) less risk of from damage due to smaller amount of pipework 4) less structural support for the smaller cwsc
direct cold water disadvantages:-
1)higher pressure may make the system noisey 2) there is no reserve water if the mains is cut off 3) more wear and tear on taps and valves due to high pressure
indirect cold water advantages:-
1) a reserve of water if mains is cut off 2)less risk of system noise due to lower pressure 3)less risk of wear and tear on taps and valves
disadvantages of indirect cold water:-
1) an increased risk of frost damage 2) more expensive to install due to bigger cwsc and pioe work
Perry's description of a direct hot water system refers to an in-line water heating arrangement. This may or may not be a combi boiler depending on the type of heating system in use. There is also a direct hot water system which incorporates a hot water storage tank or cylinder. The water here may be heated by an electric immersion heater or by a boiler.
For more information on the different hot water systems available, look at this section of the DIYDoctor site.
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