On Fri, 18 Jun 2004 01:18:47 +0100, "IMM" wrote:


"Colin eclipse 2" wrote in message
...

I know - done to death.. A customer has asked me this question. I have
come
up with the following list. Any other thoughts - sensible ones.. no need
to
start a debate about the merits - just need a list!

Conventional
Pros
Stored hot water - so water (hot and cold)
available if mains supply fails

-This is so rare an event that is it is not worth taking into consideration.

It happens to me every few months......


Immersion heater backup - hot water if boiler or gas fails
Warm airing cupboard

That can be achieved with any heating system, so not so.


Cons
Cylinder needs replacement (in this case to comply with building
regs)

-Cylinders may need replacing every 8 to 10 years in hard water areas.

One can use a water softener or phosphate doser to avoid this. If
the water is untreated, then heat exchangers on some combis are liable
to scaling.



Storing hot water not as energy efficient
More complex controls
More costly than combi to install

-Very poor shower pressure, having to use an expensive and noisy power
shower pump in some situations.

Flow from a combi can also be poor if it is not a large one.


-The cylinder takes up space.

So does a combi if of high capacity and fitted with some form of
storage.


-Ugly zone valves and pumps around cylinder.

One can have a system boiler.....




Combi
Pros
High pressure showers without pumps
Only heats hot water you use
No stored water (flooding issue)
Frees cupboard space

-No wating for cylinder to reheat

This is irrelevant if the cylinder is adequately sized.

-HIgh pressure shower after shower can be taken.

That depends on the water supply and temperature and rating of the
combi.


-Have a high output, so house warms up faster.

Than what? A system boiler can be equally effective.


-All the system is inside the one white box.

A system boiler can achieve that as well, with the exception of the
cylinder.


-No pipes to freeze in the loft

Irrelevant if they are properly insulated.



Cons
slower bath filling

High flowrate combi's are available, so not true.

We've had that debate and there are demonstrable limitations.



No warm airing cupboard

A small rad can be installed in the airing cupboard taking up no space.


A post suggesting that there are no disadvantages to combis should be
regarded as suspect. Nothing is ever as clear cut.






..andy

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