On Sun, 6 Nov 2005 14:05:34 -0000, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .
On Sun, 6 Nov 2005 12:18:50 -0000, "Doctor Drivel"
wrote:


"Andy Hall" aka Matt wrote in message
.. .
On 5 Nov 2005 10:52:19 -0800, "
wrote:


bedrooms. the initial idea is to fit a combi condenser (baxi 105 31kw
or platinium 33kw) into the airing cupboard where the hopt water tank

So there are two decisions to make. The first is whether she wants a
combi boiler and to remove having the boiler in the kitchen and
cylinder in the bedroom. Bear in mind that the water flow rate from
a combi is unlikely to be as great as is currently being achieved from
a cylinder and baths etc. will take longer to fill, especially in the
winter.

Tripe! high flow combis are available equalling any cylinder setup.

Read the whole thread and the context. The products under discussion
are not "high flow". They are in the average range. The 33kW one
does the predictable 13 litres per minute. This may be fine for the
user or it may not, but it is sensible to take all of the potential
issues into account.

You said "baths etc. will take longer to fill". Which is tripe. High flow
models are zippo. You are spreading amateur myths.

I'm sure that everybody else, including the OP understood the point,
but since you seem to want to be obtuse, let me spell it out for you:

- A 33kW combi of the type under discussion will deliver 13 litres per
minute of hot water with a temperature rise of 35 degrees.

- The temperature of the cold mains in the winter can be in the region
of 5 to 8 degrees

- Since usable shower/bath temperature is in the 40 to 45 degree
range, it follows that the filling rate, for this type of boiler, at
this rating will be 13 litres per minute.

- An existing storage system holds water at 60 degrees. It is mixed,
when running the bath, with cold water from the storage tank or the
mains to produce water at the required temperature.

- Each of the cold and hot flows of the storage system are likely to
be at least at 13 litres per minute if they are piped using 22mm pipe
(the standard). 20 litres/min is quite typical, and I suggested to
the OP that he might like to measure it if this might be an issue for
the user.

- In any event, it is highly likely that the boiler type under
consideration will fill the bath more slowly than the existing system.
Whether that is an issue for the user can then be determined.

- Therefore my comments, in the context of the appliances being
considered were entirely correct.

- I am fully aware that there are higher capacity instantaneous combi
boilers available. However, within the realms of available gas supply
in a domestic installation, once other requirements such as cooking
and other appliances are considered, it likely that the limit for a
boiler will be in the 40-45kW range. It is not a coincidence that
this is the largest model size of this type of product for the UK
market from the larger vendors. Predictably, these will produce
around 16 litres per minute.

- Beyond that, as I also mentioned, to achieve a greater HW
production rate than achievable instantaneously, some form of energy
storage is needed. This can be done externally to the boiler, viz. a
conventional cylinder, heat bank or thermal store; or within the
appliance as some form of CPSU. The performance of these depends on
the amount of water stored and at what temperature.





--

..andy