| Type of Hot Water
System |
Pressures
at Outlets
metres head |
Hot
Water Flow Rates
litres/minute |
Advantages |
Disadvantages |
| Basic: Cold Water Storage Tank coupled to
a Vented Hot Water Cylinder |
2 - 10
Increases with height of water level in cold water tank above outlet. |
5 - 40
Increases with height of water level in cold water tank above outlet, and with pipe
sizes. |
The most commonly used type
of system. Very simply and reliable system.
Flow rate not limited by mains supply pipework. |
Requires space above all
outlets for cold water storage.
Usually not enough pressure to run a performance shower. |
| As above, with the addition of a Booster
Pump |
15 - 40
As above combined with the power of the pump. |
15 - 45
As above combined with the power of the pump. |
Easiest way to upgrade a
basic system to provide high pressures and flow rates.
Flow rate not limited by mains supply pipework. |
Noise & Vibration |
| Unvented Cylinder |
10 - 60
Depends upon mains water pressure, and limited by pressure cylinder can take. |
15 - 45
Limited by pipe size of mains water supply, combined with pressure reducing valve. |
No Cold Storage. |
Cylinder is pressurised,
requiring pressure reducing valve and a variety of safety controls. Strict safety
requirements. |
| Thermal Store using a Coil to heat Mains
Water |
10 - 60
Depends upon mains water pressure. |
8 - 25
Limited by pipe size of mains water supply, and resistance of mains water coil. |
No Cold
Storage.
No Leigionella Risk.
Unpressurised and fully vented, allowing use of tanks as well as cylinders.
Mains water supply does not require pressure reducing valve.
May be heated directly by a boiler, and protected with inhibitors &
anti-freeze.
No scale build up in store. |
Water temperature tends to
drop off after a few minutes constant use. |
| HEAT
Bank Thermal Store: Thermal Store using a Plate Heat
Exchanger to heat Mains Water |
10 - 60
Depends upon mains water pressure. |
20 - 45
Limited by pipe size of mains water supply, and resistance of mains water coil. |
As above with the added
advantages of higher flow rates, and much more efficient use of stored hot water.
Requires a supply pressure of only 1 bar (10m) to obtain a good flow
rate (18 ltr/min). |
|
| Combination Boiler |
As above |
6 - 18
Limited by output of boiler. |
No Leigionella Risk.
Does away with the need for any storage. |
Often disliked because of low
flow rates. Can only usually supply a single outlet at any time. |
| Electric Water Heater |
As above |
4 - 12
Limited by output of heater. |
As above |
As above, but even worst. |
| Plate Heat Exchanger running off a
Central Boiler |
As above |
6 - 30
Limited by output of boiler. |
As above, plus large central
boilers allow for high output.
Very simple to install. |
At periods of peak demand,
output may drop. |