thanks for your reply!

In discussion with the plumber, it turned out that taking the old, but
perfectly serviceable boiler and coupling it to a mains pressure tank
and converting the rads to sealed Y plan would be the cheapest option of
all.

I take your point here. However my current system is really old and
badly
designed. It's open vented system with hot water cylinder and 15+
years old
baxi boiler. I say badly designed bacause I think I have undersized
radiators
and pipes (8mm copper). All I can get during winter is less than 20
degrees air temp.

Not wishing to put you off, just double check that what you are doing IS
the best cost-benefit..

cost benefit is the main reason - here is why I think new combi is
good idea:

1) my current boiler is old, I had few problems with it this winter
and would like to
avoid the situation where I have to replace it quickly in the worst
moment (next winter)
doing rads/piping/controls myself I can save some money. Remeber
it's the labour
cost that's the most expensive in CH
2) new boiler will be condensing model, which means savings on gas
bill
3) heating on demand is more economical from storing water
4) I can free some loft space for future conversion

do I miss some important point here ? feel free to comment

I certainly have never met a combi yet that can match my peak hot water
flows here, with a pressurized tank.
I agree. However it's only two of us in the property, so what I am
really after
is a decent flow from a shower when someone is doing the dishes.

Or can have an immersion heater if you run out of oil or gas..
As I mentioned - I plan to convert loft at some point and have a
second bathroom
with electric shower as backup. As we shower quite a lot and hot water
cylinder is a
bit to small so we use electric shower at the moment.

Nor yet one that delivers full pressure hot water even when the power
goes out..well, for a while, anyway :-)
can't argue with that =)

again thanks for your input,

Mike

wrote:
thanks for your reply!

In discussion with the plumber, it turned out that taking the old, but
perfectly serviceable boiler and coupling it to a mains pressure tank
and converting the rads to sealed Y plan would be the cheapest option of
all.

I take your point here. However my current system is really old and
badly
designed. It's open vented system with hot water cylinder and 15+
years old
baxi boiler. I say badly designed bacause I think I have undersized
radiators
and pipes (8mm copper). All I can get during winter is less than 20
degrees air temp.

Not wishing to put you off, just double check that what you are doing IS
the best cost-benefit..

cost benefit is the main reason - here is why I think new combi is
good idea:

1) my current boiler is old, I had few problems with it this winter
and would like to
avoid the situation where I have to replace it quickly in the worst
moment (next winter)
doing rads/piping/controls myself I can save some money. Remeber
it's the labour
cost that's the most expensive in CH
2) new boiler will be condensing model, which means savings on gas
bill
3) heating on demand is more economical from storing water

Is it though? If you have to run a big ****-off boiler flat out to heat
the water, is it as economical as a modulating boiler running at tickover?

4) I can free some loft space for future conversion

do I miss some important point here ? feel free to comment


The size of a smaller boiler and small (150L tank is not much greater
than a 20KW boiler.

Neither is the cost a great deal different in my case. YMMV.

To get the same sort of peak flows you need something like a 30KW
combi..this may not be an issue for you though.



I certainly have never met a combi yet that can match my peak hot water
flows here, with a pressurized tank.
I agree. However it's only two of us in the property, so what I am
really after
is a decent flow from a shower when someone is doing the dishes.


You won't get that from a combi. I stayed in a house once..with someone
with a teenage daughter. The HOWLS of anguish when I turned on a hot tap
to wash my hands from the teenage daughter showering..

We are a two person house, and believe me even a 250 liter tank only
lasts one bloody good bath or shower..but at least with thermostats the
flow may drop off, in the shower when you run a tap, but it doesn't go
cold..

Or can have an immersion heater if you run out of oil or gas..
As I mentioned - I plan to convert loft at some point and have a
second bathroom
with electric shower as backup. As we shower quite a lot and hot water
cylinder is a
bit to small so we use electric shower at the moment.

Mmm. The pressurized tank will go anywhere..doesn't have to be in the
loft. Could be in the garage..
As could the boiler.. Mines in a corner of the loft as it happens..


Nor yet one that delivers full pressure hot water even when the power
goes out..well, for a while, anyway :-)
can't argue with that =)

Seriously look closely at what peak hot water rates you CAN get with a
combi.

I was seriously disappointed. The ones that did the rates were all 1500
quid plus. So was a new boiler and PHW tank. About 750 each. less if you
shop around.

And remember, IF your gas supply can't do the peak rates, then you have
ye more expense to upgrade it.

On 23 May 2007 08:14:20 -0700 someone who may be
wrote this:-

Now,
when you store the water in the tank heat will escape and you have to
burn some more gas to keep water at temp B all the time. This is where
combi wins I think (at least in terms of energy savings)

There are two assumptions here. Firstly, that hot water cylinders
lose a lot of heat. One with double or triple insulation does not.

Secondly, that a combination boiler does not have a small not
particularly well insulated hot water cylinder inside which the
boiler will fire periodically to keep warm. Many do have one, though
it can be turned off.

Additionally if you work irregular hours you don't have the trouble of
programming when exactly you need to have your hot water.

Thermal store. Instant hot water when wanted.

Connect the central heating to it as well and one gets instant
heating by flicking a switch when entering the building. No need to
wait for the boiler to warm up the radiators. No need for a time
clock which then heats up the building even if one has been delayed.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54