"Andy Hall" wrote in message
...
On Sat, 25 Sep 2004 08:50:44 +0100, W
wrote:
Hi,
I am about to have a new heating system installed in my house. The
choice of boilers seem to come down to either a Worcester-Bosch
Highflow 400 or a Vokera Linea Max. As both of these boilers are
about the same price and have very similar specifications is there
much to choose between them? I would be interested in any independent
reliability surveys or comparative maintenance costs.
I know neither of these boilers are condensing but I can't find a
similar condensing boiler and also the vent will be very close to a
boundry so a plume might be unpopular with the neighbours.
TIA, W.
Who is suggesting the choice? Quoting installers?
Both are reputable makes, but neither
is an exciting product from the
performance point of view.
18019 litres/min is not bad at all amnd will fill a bath pronto.
Although marketed as "suitable for the
larger house", really the power levels
of 24-28kW are very average
these days.
Thye both use heated stored water, a heat bank, to boost performance.
That is not to say that you necessarily need anything
larger but rather that there is plenty of choice in this range and
above.
Both are right at the very bottom of the legal limit on what is
allowed for new boiler installations - 78% on the SEDBUK seasonaly
efficiency scale.
He said he has doubts about the condensing plume.
Condensing boilers achieve around 90-91%
efficiency, and from my own experience, the cost savings line up with
the efficiency difference.
Bear in mind that gas prices are in the process of increasing and the
trend will undoubtedly continue. If you plan to remain in the house
for a while, you will recover your costs.
Pluming on newer designs of condensing boiler are nowhere near the
level of earlier designs and on many models it is possible to use flue
systems constructed from 50mm high temperature PVC waste pipe. These
can be run some distance - even internally - and hence exhaust to a
more convenient place.
He is after a combi, no condensing combi I know eliminates the plume.
Having the water heated instantly
in a simple combi means that the hot
water flow is limited to the instant
energy is limited to that
provided by the burner.
He stated two stored water excellent flow combi's, not simple low flow low
models.
To get around it, both products you mention have a small heatbank
store of around 50-60 litres. This energy is applied rapidly to
the cold water passing through the boiler and allows the manufacturers
to quote impressive flow rates of 18 litres per minute. At 60 degrees
output and mixed with cold water, this will provide good flows for two
showers.
However, there is a catch. That is that once the little heatbank
runs out, the performance drops to the instantaneous rate and you are
very limited.
He is running a house not a school. It will very rare will drop into the
low flow stage of the combi's. But he will "never" run out hot water. The
recovery rate of these models is only a few minutes.
With the volumes listed, you will be able to fill a
bath, not very deeply before the store runs out - approx 100 litres
total.
100 litres is the average bath size. Any more water and it fill at the lower
flowrate of combi. this can be running while people are actually in the
bath, as many people,do anyhow. They can in when there is only a few inches
of water and leave the taps on.
A reasonable bath needs closer to 150 litres.
Two showers will run for a very few minutes
on it if run together.
Average shower of 7 - 8 litres/minute at approx 40C. So 2 showers will take
15 litres of mixed water. Of the 15 litres 2/3 to 3/4 will be hot and the
rest cold of the 60C draw-off temperature, so only 10 litres/min will be
drawn off the 60 litre 80C temperature stored water heat bank. Then you have
to take into account that on draw-off the heat bank always fires up
providing approx 11 litres/min. In effect the stored water supplies one
shower, the instant side doing more than the other. As the instant side is
infinite and never runs out, the stored water alone will provide one of the
showers. The 60 litres at 80C will keep one shower running for about 13
minutes. So, two average shower will run simultaneously for approx 13 - 15
minutes, not a few minutes.
Please do not give opinions of equipment you have even seen never mind seen
them in action. Those I have met who have these sort of combi's love them
and would never go back to tank/cylinder/power shower pump dross. The poster
is attempting gain information to make a reasoned decision. The last thing
he needs is misinformation from an amateur.
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