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Mains Pressure Hot Water
Heatrae Sadia Amptec Electrical Boilers
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| Mains
Pressure Hot Water Systems and Products |
....the
options |
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| This simple
guide will help you understand how mains pressure hot water systems work,
and help you to compare products from different manufacturers. |
Mains Pressure Hot water
Systems - Explained
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| You may be considering installing
new, or changing an existing system to provide mains pressure hot water at
your taps.
This may be an ideal choice for you, but
before you make your decision understand how these systems work and consider all the facts. |
| Any system providing a mains
pressure supply is only as good as the supply entering the property. A
product may boast for example - 35 litres per minute flow rate at 3 bar
pressure - but if the supply to your property is inadequate and can only
muster say 15 litres at 1 bar, this is all you will achieve. Figures quoted
against products are indicative of their potential based on an adequate
supply. |
| In general, a mains pressure
system comprises a means of heating water taken directly from the incoming
water main prior to delivery to your tap. There are several ways to do this
and many different manufacturers interpretations on product design. |
There are two main types of
domestic Mains Pressure Hot Water Systems.
- Unvented Mains Pressure Systems
- Vented Mains Pressure Systems
The term vented refers to whether the system
is partially vented to atmosphere or completely pressurised and therefore
unvented. |
Unvented Mains Pressure
Systems
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| In an unvented system, incoming
cold mains water typically enters a pressure vessel (for example: a Megaflo
made by Heatrae Sadia, or a 'Vantage'
made by Vaillant - there are of course others)
where it is heated either Directly by means of electrical heater/s, or
Indirectly by means of a primary heat exchanger within the vessel being
supplied by your central heating boiler. The hot water stored within the
vessel is forced out by the incoming cold water when you open a tap
hence - Mains Pressure Hot Water. |
Vented Mains Pressure Systems
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| In a vented system, heat is
imparted to the incoming mains water by means of a secondary heat exchanger
within the vessel. Water in the vessel is used rather like a battery for
heat - a Thermal Store.
The incoming mains water passes through it's heat exchanger within the
vessel drawing heat from the store. The Thermal Store temperature is
maintained in the usual way - either Directly with electrical heaters, or
Indirectly by your boiler.
Because the water within the Thermal Store
does not need to be under pressure (as with an unvented system) it is vented
to atmosphere. The body of water within the Thermal Store is used purely as a medium for
storing and imparting heat to the secondary exchanger. |
Unvented and vented systems both
provide hot water at mains pressure. They achieve this by slightly different
methods. There are however certain considerations when choosing the system
that suits you best.
Unvented Mains Pressure
Systems
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- In an unvented system you will be storing
a large volume of hot water under pressure. For reasons of safety such
systems must be installed by qualified technicians with relevant
experience, CITB training and G3 certification.
- As a precaution, pressure-relief pipework
and valves must be installed to protect against unsafe pressure build-up
within the vessel which could result in explosion.
- Your Local Authority (Building Control
Dept) will need to be advised of your intention to install an unvented
system.
- For reasons of safety, your system will
require annual maintenance to ensure safety equipment is functioning
correctly (BS2870).
- An unvented system must be commissioned
and certified by the installer.
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Vented Mains Pressure
Systems
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|
- A vented system does not store a large
volume of hot water under pressure. The Thermal Store, whilst containing
hot water, remains at atmospheric pressure.
- There are no hazardous issues with a
vented system. Pressure relief valves and pipework are not therefore
required.
- Vented systems do not require Building
Control approval.
- Because of the simplicity and safety of
such systems, installers do not need certification or specialist
training.
- Vented systems do not need certification.
- There are no special annual maintenance
requirements.
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| Drawbacks of a
mains pressure hot water system |
| Under water bye-laws you may not
add a pump directly to your mains fed system to increase pressure or flow
rate. If the supply in your house is poor there will be no simple way to
improve it. Additional performance usually entails bringing in a new, larger
supply pipe to the property. Even then, you should ensure the new improved
supply will be adequate, as some areas suffer from frustratingly low
pressure.
Always remember - your system can never be
better than the supply to it.
Mains pressure systems are at the mercy of
fluctuations in supply pressure. This may not be an issue in the majority of
cases.
Mains pressure systems can give 'power shower'
performance, providing supply pressure is good. If you like a vigorous
showering experience and your supply pressure is poor, remember - you cannot
install a shower booster pump.
If you simply must have a power shower
then consider a gravity fed system. You
can do pretty much anything you want with a gravity feed. |
Compared
-
The Good 
and
the Not So Good 
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| And
Finally........ |
Make sure you check out the comparable -
 Cost
of purchase |
Installation |
Safety |
| Maintenance |
Flow rate potential |
General
running costs |
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