"Andy Hall" wrote in message
...
On Sat, 25 Sep 2004 14:40:07 +0100, "IMM" wrote:


"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.

It would be outstanding,

I don't think he wants, or needs, firehose volumes and pressures.

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.

I covered that.


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.

There is, however a range of effects.

Even a conventional boiler will produce a plume on cold dry days.

Only slight.

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.

I'm aware of that, which is why I said "in a" and not in "the ones
that were mentioned". I then went on to discuss the effect of
adding a small store.

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.

The storage capacity is very limited as was demonstrated last week.

You never.

No specifics on what "large house" meant, or indeed the numbr of
bathrooms and pattern of use. I therefore described what could
happen under patterns of use that are entirely possible in a large,
but not that large house. it is possible that two bathrooms are in
use simultaneously and peak demands are high. I certainly have that
situation, and it is not at all unusual.

Obviously if the OP's needs are less, then the situation will be
better and a small store combi may be OK.

I have simply stated what could happen under quite possible
circumstances, not hoped that it won't.

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.

It's a small bath.

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.

That makes no sense in English at all.


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.

That is not an average shower at all.

It is an average shower!!!!!!!!!

So 2 showers will take
15 litres of mixed water.

It needs at least twice that.

So 2 showers will take 15 litres of mixed water!!!!!!!!!!

snip garbage

The poster
is attempting gain information to make a
reasoned decision. The last thing
he needs is misinformation from an amateur.

So why are you giving it?

Because I know what I am on about and you clearly do not.