Deciding on one or the other depends on having a ‘direct’ or ‘indirect’system.
Either directly into the unvented hot water/ pressure vessel contained within a cylinder,
Or how the water is heated within the hot water cylinder
either directly using an electric immersion heater or indirectly
using a heat exchanger supplied from a boiler.
with indirect for normal heating and an immersion heater as a
back-up or storage for extra hot water at short notice.
A vented cylinder has a vent pipe which allows it to be subject to atmospheric pressure.
The mains water is fed to and stored in the cold water storage tank (usually in the loft),
and from there it goes to the appliances in the home.
Because the water supply is gravity-fed and therefore low pressure,
sometimes a pump needs to be added to assure a strong flow of water both for the domestic hot water and the heating.
The principles of heating are the same as vented by using an emersion heater rather than a heat exchanger,
but because the pressure comes directly from the mains water the flow is much better.
You may find you have a small tank in the loft for venting and feeding your central heating, there is no need for a cold water storage tank.
The main advantages of installing vented hot water cylinders – like a
Heatrae Sadia Megalife vented water cylinder – over an unvented alternative
is that they are much less complicated – making them easier to install – and cost less to buy and maintain.
is the fact you need to have a cold water storage tank so the system
will ultimately take up more space than an unvented hot water cylinder.
the water will be heated indirectly by a primary heat exchanger within the unit being supplied by the boiler.
The heat exchanger is a much more economical option
But if something goes wrong with your boiler, you’re left without any hot water at all until it’s repaired.
Because unvented cylinders – like the Baxi Megaflo HE – provide hot water constantly at mains pressure,
there is no requirement for a cold water storage tank and the extra pipework to link it up.
And because you’re relying on the pressure from the mains rather than just gravity,
The biggest domestic issue is that you cannot use an unvented hot water cylinder with some power showers and some mixers.
making them pricier than traditional vented hot water cylinders.
Using an immersion element to heat the water means you’re relying on electricity
which means less reliance on your boiler but it will be more expensive to run it
as electricity is far more expensive than a heat exchanger.
Hot water cylinder capacity varies between 25 to 50 gallons for normal domestic
Most cylinders are made from thin copper and you should make sure your cylinder is well insulated to prevent heat loss.
Insulated cylinders are available, which are coated with foamed polyurethane.
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Duval Heating 1985 - 2019