I think your questions 1-5 have been answered by the other replies.
I'm not an expert, but have gone through this myself recently. In
making a choice you need to consider many things like cost,
installation and efficiency.
- Cheaper to install.
- No header tank required.
- Does not need airing cupboard.
- Takes longer to fill bath.
- Hot water at (almost) mains pressure.
- Hot water at lower pressure.
- Quicker bath filling.
- Showers may need boosting.
There are other types of system which store water at a higher pressure
or use stored water to heat the hot water which you may wish to
Here is a run down on combi's:
Firstly, a combi is a "combination" of the heating and water system in one
case, eliminating external tanks and cylinders, and generally supply hot
water at high main pressure. To confuse a little, some can run at very low
pressures and even off tanks. Generally most are fed from the mains. It is
generally a matter of mounting the boiler and connect up the pipes. The
expert designers have done the hard work for you and put all in one case.
Types of combi:
1) The Infinitely Continuous Combi -
Heats cold mains water instantly as it runs through the combi. It never runs
out of hot water. This is the most common type of combi, generally having
lower flowrates than Nos 2 & 3 below. The largest flow rate instant combi is
a two bathroom model, 22 litres/min ECO-Hometec. Being a condenser it is
very economical too. http://www.eco-hometec.co.uk
2) Unvented Cylinder Combi -
An unvented cylinder is a similar to a conventional cylinder but run off the
high-pressure cold mains. A combi with an integral unvented cylinder has
approx 60 litre cylinder heated to approx 80C, with a quick recovery coil
that takes all the boilers output. A fast acting cylinder thermostat ensures
the boiler pumps heat into the cylinder ASAP with a recovery rate from cold
around 5-8 mins (Ariston claim 8 mins). The 80C water is blended down to
about 45-50C. e.g's, Ariston Genus 27 Plus, Glow Worm, Powermax, Alpha
3) Infinately Continuous/Unvented cylinder combi -
An example being the Alpha CD50, a combination of both having a two stage
flowrate, of high flowrate when using the stored water with an automatic
flow regulator switching in to reduce flow to an infinately continuous
flowrate of approx 13-14 litres/min.
4) Heat Bank Combi -
Incoming water is instantly heated running through a plate heat exchanger
(as is most instantaneous combi's) that takes its heat from a "domestic hot
water only" store of water at approx 80C (instantaneous combi's take the
heat from a heat-exchanger heater via the burner). A fast acting thermostat
ensures the boiler pumps all of its heat into the store ASAP with a recovery
rate about 5-8 mins from cold. The 80C water is blended down to about
45-50C. They are generally two stage flow rates, in that when the thermal
store is exhausted it reverts to what the burner can produce, which is
approx 11-12 litre/minute. e.g. Vokera & Worcester floor standing models
(standard washing machine sizes).
N.B. The heat bank is a variation of a thermal store, but is "not" a thermal
store in the conventional sense in that a coil carrying cold mains water
runs though a store of hot water kept at about 80C. Heat-banks are far more
efficient and give higher flowrates than conventional coiled thermal stores.
The stainless steel plate heat-exchangers do not scale up so easily.
5) Combined Primary Storage Unit
(Not classed as a combi, but a derivative of a combi, but still a one box
solution, so still in the same family)
These are a combination of a large thermal store, or heat bank, and boiler
in one casing. The units are large (larger than standard washing machine
size) and floor mounted. The heating is taken off the thermal store, which
in many cases the DHW taken off the store using a plate heat-exchanger
(heat-bank). Unlike the Heat-bank in 3) above the thermal store supplies
heating "and" DHW, giving the "combined" to the title. They are available
from 1 to 2.5 bathroom models. Gledhill do an excellent condensing
version, the Gulfsream 2000. http://www.gledhill.net
Nos. 2), 3), 4) & 5) have high flowrates. No. 1 "generally" has low
flowrates but there are always exceptions and some can be high - e.g. the
ECO-Hometec infinitely continuous combi, actually has a very high flowrate.
Nos 2), 3), 4) & 5) use stored water, but in different ways. Unlike No. 1
"some" versions will eventually run cold, but that takes quite a time, hence
some are referred to as "two bathroom" models, having the ability to fill
two baths with very fast recovery rates. As hot water is being drawn off
the high rating burner is also reheating. Very rare do these combi's run
out of hot water in average use. When taking one shower the burner may be
re-heating faster than what can be drawn-off. No. 3) above uses stored
water but will not run out of hot water (high and low flowrates). Most
versions of No. 4) above are two stage flowrate models (high and low
flowrates) and will also not run out of hot water.
There are combi models that give hot water and heating simultaneously as
Combined Primary Storage Units do. Most don't as they are hot water
No one gives a flying f*ck about your posts Dribble. The sales of
combi's are rapidly plumetting as the benefits of stored hot water
systems are being recognised by a generation of people brainwashed by
idiots like you. Copper sales are booming too. Now bugger off back
into your closet and take a few tablets, preferably the whole packet
you sad tw*t.
Not you, just Dribble :-) , a part time plumbing counter assistant,
who is solely responsible for flooding across huge areas of a North
London council estate where the gas, water and electricity are still
cut off on the grounds of safety. Drivel has a strange fascination
with Combi boilers, dismissing storage systems without any regard for
the users requirements. Some have put this down to the fact he wasn't
breast fed, others to a strange incident involving his mother and a
randy plumber fitting a copper tank . True but sad.
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