On Wed, 12 Jul 2006 20:41:01 +0100, Doctor Drivel wrote:
"Ed Sirett" wrote in message
news
On Tue, 11 Jul 2006 18:37:29 +0100, Doctor Drivel wrote:
"Ed Sirett" wrote in message
news
On Mon, 10 Jul 2006 21:20:13 +0100, Willi wrote:
I will be looking for wall hung, condensing, good efficiency. Not
Combi,
for a 4 bedroom house. vented fully pumped system.
.....are you a member of the flat earth society as well?
Dr Drivel
Can i ask what makes you say that? Are you saying you would rather have
a
Combi?
I will consider all options. (but not warm air, however good they are
now).
What are the advantages of a Combi? I guess space as a hot water tank
is
not
required, but what are the others?
Regards, Will
It's probably time you had a look at the boiler choice FAQ and the
heating
section of the main FAQ.
I would say give it a miss as it's 20 years out of date. Get it updated.
You have made this comment several times of late.
I would be happy to update the FAQ if you could be more specific.
Here is the post. The FAQ parts in quotes.
Have a read of the BoilerChoice FAQ it may help.
Or may not:
"Vented HW cylinder.
This is still the norm for most houses. With a modern cylinder and correct
controls there should be no problem with running a bath every 15-20 minutes.
Cylinders are now required to have a good level of insulation (not the old
jacket insulation). New replacement cylinders will be able to heat the whole
cylinder from cold in around 20-25minute,"
20 to 25 minutes? Only a quick recovery cylinder can do this. The normal
Part L is rated at 30 minutes warm up if all criteria is met in boiler
temperatures, flow, etc. A quick recovery with a condensing boiler can
reheat in 10 to 15 minutes depending on boiler size. They also enhance
condesning efficiency. There is no mention of quick recovery cylinders in
this FAQ.
The relevant standard mentions times around 20 minutes - for Part L
compliant cylinders. Suggestion not upheld.
"Unvented HW cylinder:
Offers HW at mains pressure together with excellent flow. These are
expensive and can only be installed by qualified people. To justify the
expense you really need to have an excellent water main at least 25mm
diameter plastic pipe. Results will be adequate but probably not worth the
cost if used with an ordinary lead or 20mm plastic incomers. "
The all important annual service is omitted. It will cost £60-100 a year to
have serviced. That is over £2,000 over 20 years. They also have the
potential to explode:
The potential to explode is eliminated by having the only possible method
of heating which could cause a problem (electricity) to have two
thermostats (one of which locks out) also there are two pressure relief
valves, and one temperature relief valves.
There is no manadatory requirement to have the unit serviced and frankly
the guarantees are either so limited or never likely to be needed.
It is possible to create a hazard by incorrect installation as indeed it
is with a vented cylinder (I've seen one this year with a valve on the
outlet vent pipe).
NO change.
"Thermal sto
Offers most of the advantages of the Unvented cylinders, costs are similar
but may be diy installed. The flowrate is still pretty good (around 20
litres/min). Can be used to integrate other sources of heat (solid fuel,
solar) or facilitate underfloor heating."
No mention of the heat bank variant of the thermal store (Heat banks use
plate heat exchangers, stores use coils), which can give flowrates of 40
litres/min or more.
Too much detail. Splitting semantic and linguistic hairs is not my style.
I might add "at least 20 litres/minute or more".
"Normal combi boiler:
Heats water only when it is needed. Instant availability (after the HW has
drawn through and the boiler settled down - about 10-40 seconds).
Never runs out. Simplified installation. Rather limited flow rate. "
Know as an "infinitely continuous" combi, not a normal combi. Some models
have very high flowrates that fill baths very fast indeed, and can do 2
bathrooms (MAN made in Germany), although these are not available in the
local plumbers shop being special order.
"Small storage combi:
As above but holds a store of HW to give a prompter response and improved
flow rates for a while until the stored HW has run out. "
The above are to eliminate the combi lag at the taps, giving faster hot
water. This was not explained.
I think the explanation says 'prompter response' - how is that a failure
to explain. Much of the lag is the pipe work and such a boiler will not
make any difference to that aspect.
"Large storage combi:
Washing machine sized floor standing combi boiler. Contains pretty much all
of the benefits of a HW cylinder whilst still having a simplified
installation. Saves the space that a HW cylinder would take.
There are multiple decisions to be made based on trades-off between size,
cost, flow rate, warm up times etc."
Some are larger than washing machines sizes. Some can supply three baths
(Gledhill Gulfstream), ACV Heatmaster. All have no cold water tanks.
Covered by the term 'simplified installation'.
No mention of high flowrate wall mounted combis like the Alpha CD50, which
is a mix of the infinitely continuous combi and a stored water combi. It is
a two stage flowrate (high and low) and never runs out of hot water.
Covered by the comment about a 'spectrum of models'.
I might add ...typically a large floor mounted unit although some are
wall mounted ...
No mention of high flowrate multi-point water heaters like the Rinnai and
Andrews (relatively new innovations in the UK), which can also be fitted
outside saving much space inside a house, and do two bathrooms. A small CH
boiler and an outside high flowrate Rinnai will be about the same price as a
boiler and an unvented cylinder, probably less, and takes up no space in the
house and never runs out of hot water. And if the boiler is down the DHW
still runs. Also no troublesome CH zone valves on the CH system making a
simpler and more reliable installation. Rinnais have interior models too.
Rinnais are ideal for multi-jet showers (a newish innovation). An unvented
cylinder would have to be "very" large, and expensive, to compete with the
output of a Rinnai.
This FAQ is misleading and omitting information of modern equipment and ways
gives a distorted ill-informed view. I would not recommend people take this
FAQ seriously as it is only applicable to 1986.
The FAQ is written to help a variety of people including those who might
not even know about a combi or a condensing boiler (or might
even believe those terms were opposites).
The FAQ does not contain the very precise and detailed
descriptions of the slightly different shades of combi boiler (some of
which are much more functional than many people may have experienced).
If in a thread it turns out the the discussion can usefully delve into
these matters that's fine. The purpose of the FAQ is save time and effort
by answering the _bulk_ of the questions so that the effort can be
focused on specifics in a thread.
You are welcome to write you own comprehensive guide to combi boilers and
host it yourself.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at
http://www.diyfaq.org.uk
Gas fitting FAQ
http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ
http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ
http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he
http://www.makewrite.demon.co.uk/GasFittingStandards