We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.

On Tue, 02 Dec 2003 18:37:38 GMT, Chris
-o-m wrote:

We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.

The main operational points with having a roof tank are

- you are not limited to the delivery rate of the mains supply, so
can run, for a period of time, multiple showers and baths. This is
also true of mains derived systems as long as the mains supply is
adequate but should be checked.

- that the water using appliances can be independent of one another as
regards flow. This can be achieved almost as well with mains
connections if the plumbing is organised appropriately and the
possible use of flow restrictors.

- that you have a store of water if the mains fails


Hopefully, your installer will have checked that the mains flow rate
(not the pressure so much) is adequate. If it is less than about
20 litres per minute at the kitchen cold tap you could have problems
if you are looking for good shower and bath filling performance.
You can check this yourself by timing how long it takes to fill a
measured container like a bucket.

Secondly, hopefully your installer is fitting an adequately sized
combi boiler. Your existing system heats the water in the cylinder
to 60 degrees or thereabouts and you get to use almost all of it as
quickly as you like. You heat the water over time to reach that
point.

With a combi, the effect is different. You are applying a fixed
amount of heat to cold mains water which varies in temperature during
the year and in flow rate. Combi boilers are specified in terms of a
flow rate for a 35 degree rise in temperature and the commonly sized
boilers will deliver 11-15 litres per minute according to rating.
In the summer this is OK, but in the winter, the mains water is down
to 5-8 degrees. You can work out from this that under these
conditions, the output temperature will be at around 40 degrees which
is shower temperature, not hot water. So in effect, the rated
output of the boiler is what you will get from the shower in the
winter and/or a lower flow rate if you want hotter water.

All of this can be OK if your requirements are modest or you have a
large boiler. Note that for combi boilers the heat output to the CH
normally modulate downwards, so that even if you choose a large boiler
from the HW standpoint, it does not mean that it is necessarily
oversized for the house.

Take a look at the spec. of the proposed boiler and make sure that you
are happy with what it will do. You can simulate the flow rate by
experimenting with turning a tap to a given level and measuring the
rate as before.

The other factor, is that depending on the plumbing layout, you may
experience more or less interaction between appliances. On a newly
planned and implemented system designed for mains pressure operation
this can be done quite easily, but more may be involved when modifying
an old system in terms of new pipe runs.






..andy

To email, substitute .nospam with .gl

Chris wrote:

We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?



Not really, no. I have seen the setup you describe used a lot - in fact
you can get HW tanks witha header on top of them. This has often been a
simple upgrade for older properties with gravity HW systems anyway - rip
out old tank, header tank, wire all cold taps to mains, and install
small HW tank and immersion in wardrobe.

You want mains cold anuyway with a combi, since HW is now mains
pressure. And you can rip out the HW tank as well.


Thanks Chris.

"Chris" -o-m wrote in message
...
We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.


I presume that the header tank in the airing cupboard is for the existing
hot water system? It's quite normal to feed all the cold taps directly off
the mains rather than from a header tank. When your existing boiler is
replaced by a combi, you'll presumably no longer have a stored hot water
system - so the hot cylinder and header in the airing cupboard will
disappear. [How will you air the washing?]

I presume that there must be an additional small header tank somewhere for
the primary heating circuit? Perhaps it's in the attic, buried in dead
flies and lagging? [As far as I am aware, Baxi Bermudas were designed for
vented rather than sealed systems]. Your replacement system will have a
sealed - pressurised - primary circuit with filling loop, pressure vessel
and pressure gauge - so this additional header will also disappear.

FWIW, I've never been totally convinced about combis - except for small
flats or single occupancy buildings - and would prefer always to have stored
hot water. It's worth asking some pertinent questions to satisfy yourself
that a combi will really do everything you expect of it before going ahead
with this scheme.

Incidentally, although it's not too common, you *can* have stored hot water
with a combi - if you use the hot water side just for the kitchen tap and
maybe a shower - and zone the heating side so that it also heats a tank of
hot water via an indirect coil in the cylinder as per your existing system.
That would fill a bath *much* faster.

Roger

On Tue, 02 Dec 2003 18:37:38 GMT, Chris
-o-m wrote:

We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.


Existing header tank is for hot water tank and the proposed combi is a
Baxi 105e. The mains CW flow rate certainly seems adequate, i'll try
and quantify it tomorrow.

From the replies so far it would seem that the current arrangement is
not an issue.

Thanks for the replies so far.

Chris.

On Tue, 02 Dec 2003 20:54:59 GMT, Chris
-o-m wrote:

On Tue, 02 Dec 2003 18:37:38 GMT, Chris
-o-m wrote:

We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.


Existing header tank is for hot water tank and the proposed combi is a
Baxi 105e. The mains CW flow rate certainly seems adequate, i'll try
and quantify it tomorrow.

This boiler has a DHW flow rate of only 12.7 litres/min for 35 degree
rise. I would suggest looking at that carefully before committing,
and see if you are happy with it at 40 degrees, less at higher
temperatures.

It is also a very poor choice from the energy efficiency perspective.
At 78.5% SEDBUK rating it is only just scraping into the bottom end of
the requirements of the Building Regulations which require 78%.
The Baxi Bermuda is at 72% if it's an old one, so you are gaining very
little energy saving.

It is likely from next year or the following that the requirement will
move to 86%, which will effectively take non condensing boilers off
the market.

You would be much better off with a condensing combi boiler and
perhaps a more powerful one than the 105e. Efficiencies are in the
90-91% range. I replaced an older 65% efficient wall mount boiler
with a condensing model and the reduction in gas consumption is pretty
much as you would calculate from the above numbers.
A condensing model will cost around £150-200 more for equivalent power
level, a little more for a more powerful model. You can calculate
the payback period, but it is generally well within the lifetime of
the boiler.









From the replies so far it would seem that the current arrangement is
not an issue.

Thanks for the replies so far.

Chris.



..andy

To email, substitute .nospam with .gl

"Andy Hall" wrote in message
...
On Tue, 02 Dec 2003 20:54:59 GMT, Chris
-o-m wrote:

On Tue, 02 Dec 2003 18:37:38 GMT, Chris
-o-m wrote:

We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.


Existing header tank is for hot water tank and the proposed combi is a
Baxi 105e. The mains CW flow rate certainly seems adequate, i'll try
and quantify it tomorrow.

This boiler has a DHW flow rate of only 12.7 litres/min for 35 degree
rise. I would suggest looking at that carefully before committing,
and see if you are happy with it at 40 degrees, less at higher
temperatures.

It is also a very poor choice from the energy efficiency perspective.
At 78.5% SEDBUK rating it is only just scraping into the bottom end of
the requirements of the Building Regulations which require 78%.
The Baxi Bermuda is at 72% if it's an old one, so you are gaining very
little energy saving.

It is likely from next year or the following that the requirement will
move to 86%, which will effectively take non condensing boilers off
the market.

You would be much better off with a condensing combi boiler and
perhaps a more powerful one than the 105e. Efficiencies are in the
90-91% range. I replaced an older 65% efficient wall mount boiler
with a condensing model and the reduction in gas consumption is pretty
much as you would calculate from the above numbers.
A condensing model will cost around £150-200 more for equivalent power
level, a little more for a more powerful model. You can calculate
the payback period, but it is generally well within the lifetime of
the boiler.

Try the :

""
Greenstar 40HE Plus Inc Clock & Flue
Output - 11.4 - 39.1 kW . 38,900 to 133,409 Btu's

Domestic Hot Water Flow Rate - 16 L/min
Built in fault diagnostic display.

SEDBUK Band - A
97% Efficiency
Condensing In DHW Mode

Price Includes Flue, Clock and Delivery.

Price £1,351.25 Including VAT
""

http://www.discountedheating.co.uk/s...40HE_PLUS.html

16 litres/min flowrate will give excellent performance and low bills.


---
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Version: 6.0.542 / Virus Database: 336 - Release Date: 18/11/2003

"Roger Mills" wrote in message
...

"Chris" -o-m wrote in message
...
We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.


I presume that the header tank in the airing cupboard is for the existing
hot water system? It's quite normal to feed all the cold taps directly off
the mains rather than from a header tank. When your existing boiler is
replaced by a combi, you'll presumably no longer have a stored hot water
system - so the hot cylinder and header in the airing cupboard will
disappear. [How will you air the washing?]

In the same cupboard with vastly more space with a small bathroom radiator
inside.

I presume that there must be an additional small header tank somewhere for
the primary heating circuit? Perhaps it's in the attic, buried in dead
flies and lagging? [As far as I am aware, Baxi Bermudas were designed for
vented rather than sealed systems]. Your replacement system will have a
sealed - pressurised - primary circuit with filling loop, pressure vessel
and pressure gauge - so this additional header will also disappear.

FWIW, I've never been totally convinced about combis - except for small
flats or single occupancy buildings - and would prefer always to have
stored
hot water.

There are some 2 bathroom conbi's about. use one of those and you will be
very convinced. You cisl also couple two cpmbi's toigether and see how they
sing. Combi's are cheap!

It's worth asking some pertinent questions to satisfy yourself
that a combi will really do everything you expect of it before going ahead
with this scheme.

I woudl go for a 15-16 litres/min job.

Incidentally, although it's not too common, you *can* have stored hot
water
with a combi - if you use the hot water side just for the kitchen tap and
maybe a shower - and zone the heating side so that it also heats a tank of
hot water via an indirect coil in the cylinder as per your existing
system.
That would fill a bath *much* faster.

That is true, and in many cases the ideal solution as it saves spending £250
on a power shower pump alone. Use a combi cylinder cold tank and hot water
cylinder combined and stick it in the loft and many problems solved.




---
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Version: 6.0.542 / Virus Database: 336 - Release Date: 18/11/2003

"IMM" wrote in message
...

"Roger Mills" wrote in message
...

FWIW, I've never been totally convinced about combis - except for small
flats or single occupancy buildings - and would prefer always to have
stored
hot water.

There are some 2 bathroom conbi's about. use one of those and you will be
very convinced. You cisl also couple two cpmbi's toigether and see how
they
sing. Combi's are cheap!


Yes, but in addition to the rate of heat input, there is an additional
constraint around the rate at which the mains can supply cold water.

Roger

On Tue, 02 Dec 2003 20:54:59 GMT, Chris
-o-m wrote:

On Tue, 02 Dec 2003 18:37:38 GMT, Chris
-o-m wrote:

We just moved house and next week we are getting the existing baxi
bermuda back boiler removed and replaced with a combi (with new rads
etc). The bathroom airing cupboard currently contains the HW cylinder
and header tank and I had assumed that the CW header tank would ben in
the loft. Having had a mooch up there yesterday there is nothing other
than a few dead flies and load of lagging. It would appear that all
our CW feeds currently come off the mains CW.

What are the implications of not having a CW header tank? Is it even
an issue?

Thanks Chris.


Existing header tank is for hot water tank and the proposed combi is a
Baxi 105e. The mains CW flow rate certainly seems adequate, i'll try
and quantify it tomorrow.

From the replies so far it would seem that the current arrangement is
not an issue.

Thanks for the replies so far.

Chris.


If you have no cold water tank I would strongly recommend that you
make sure you fill your kettle each night before you go to bed. Mains
water interruptions are few and far between, but not unknown. I do
not like to wake up with no means of making a drink - been there, done
that. With a cold water tank, at least you usually have a tap
(usually the bath) which can give you water that is drinkable after
boiling.