I am thinking of replacing my conventional central heating and hot
water system with a gas combination boiler, for my four bedroom
extended semi, with one bathroom. My present system is 25 years old,
when I did the heating calculations and ended up with a 10kw boiler,
which works perfectly well with ample heat output, even in the coldest
weather. When I did the heating calcs, the house was *very* well
insulated, and I have continued adding insulation/double glazing over
the years, so it is now *extremely* well insulated. I am therefore
looking for a combi with less than 10kw output to central heating,
plus enough say 10l/m to the DHW.

Objective is to save space.

I have looked in Google Groups for old threads, and tried to answer
the questions which may be asked.

Kitchen tap gives 16l/m
Bath tap hot water gives 9l/min
Soft water.

Googleing for combination boilers only gives huge 20+kw models does
anyone here know of anything smaller?

As I will now be pressurizing the central heating pipes (copper with
Yorkshire fittings) does anyone expect problems with this?

--
Dave Fawthrop dave hyphenologist co uk
"Intelligent Design?" my knees say *not*.
"Intelligent Design?" my back says *not*.

In message , Dave Fawthrop
writes

I am thinking of replacing my conventional central heating and hot
water system with a gas combination boiler, for my four bedroom
extended semi, with one bathroom. My present system is 25 years old,
when I did the heating calculations and ended up with a 10kw boiler,
which works perfectly well with ample heat output, even in the coldest
weather. When I did the heating calcs, the house was *very* well
insulated, and I have continued adding insulation/double glazing over
the years, so it is now *extremely* well insulated. I am therefore
looking for a combi with less than 10kw output to central heating,
plus enough say 10l/m to the DHW.

Objective is to save space.

I have looked in Google Groups for old threads, and tried to answer
the questions which may be asked.

Kitchen tap gives 16l/m
Bath tap hot water gives 9l/min
Soft water.

Googleing for combination boilers only gives huge 20+kw models does
anyone here know of anything smaller?

As I will now be pressurizing the central heating pipes (copper with
Yorkshire fittings) does anyone expect problems with this?


Dave,

AFAIK, You have to look at Heating and DHW separately. Whilst 10Kw might
be enough for Heating, you need much more to get a decent temperature
rise and flow for DHW. It looks like 24Kw gives a 9l/m flow with a 35C
rise in temp, and you wouldnt want any less than this. In fact, having
had 24Kw boilers, I would definitely buy a more powerful one the next
time - for DHW, not heating.

Hope this helps - Others who are experts may give a better answer.

--
Richard Faulkner

"Dave Fawthrop" wrote in message
...

I am thinking of replacing my conventional central heating and hot
water system with a gas combination boiler, for my four bedroom
extended semi, with one bathroom. My present system is 25 years old,
when I did the heating calculations and ended up with a 10kw boiler,
which works perfectly well with ample heat output, even in the coldest
weather. When I did the heating calcs, the house was *very* well
insulated, and I have continued adding insulation/double glazing over
the years, so it is now *extremely* well insulated. I am therefore
looking for a combi with less than 10kw output to central heating,
plus enough say 10l/m to the DHW.

Objective is to save space.

I have looked in Google Groups for old threads, and tried to answer
the questions which may be asked.

Kitchen tap gives 16l/m
Bath tap hot water gives 9l/min
Soft water.

Googleing for combination boilers only gives huge 20+kw models does
anyone here know of anything smaller?

As I will now be pressurizing the central heating pipes (copper with
Yorkshire fittings) does anyone expect problems with this?

firstly ignore the heating requirement and concentrate on the hot water
side - 40kW gives 16 litres per min approx - look for one that will modulate
down to your 10kW for the heating
FWIW - I have just had an Alpha CD50 fitted and am well impressed - this
modulates from 6.3 to 29.7 kW on heating and upto 32kW for water, it has a
small store for instant hot water and is wall mounted ( in loft on gable
end )
LMK if you want more info

Regards Jeff

In article ,
Dave Fawthrop wrote:
I am thinking of replacing my conventional central heating and hot
water system with a gas combination boiler, for my four bedroom
extended semi, with one bathroom. My present system is 25 years old,
when I did the heating calculations and ended up with a 10kw boiler,
which works perfectly well with ample heat output, even in the coldest
weather. When I did the heating calcs, the house was *very* well
insulated, and I have continued adding insulation/double glazing over
the years, so it is now *extremely* well insulated. I am therefore
looking for a combi with less than 10kw output to central heating,
plus enough say 10l/m to the DHW.

With a modulating condenser, the maximum heat output isn't so much of an
issue, since unlike older boilers it will actually increase efficiency
when not running at full output.

Objective is to save space.

Then it's a good choice.

I have looked in Google Groups for old threads, and tried to answer
the questions which may be asked.

Kitchen tap gives 16l/m
Bath tap hot water gives 9l/min
Soft water.

This is the existing storage system? Normally, the bath is fed from larger
bore pipe and should give much better flow - even although if a floor
higher and with less 'head'.

Googleing for combination boilers only gives huge 20+kw models does
anyone here know of anything smaller?

With a combi, you need to size it for decent hot water flow - especially
if you like big baths. This is the real problem with them - they generally
can't fill a bath anywhere as fast as a *decent* storage system.

As I will now be pressurizing the central heating pipes (copper with
Yorkshire fittings) does anyone expect problems with this?

No - they'll be fine.

--
*Be more or less specific *

Dave Plowman London SW
To e-mail, change noise into sound.

On Sun, 28 Aug 2005 18:12:22 +0100, "Dave Plowman (News)"
wrote:


| This is the existing storage system? Normally, the bath is fed from larger
| bore pipe and should give much better flow - even although if a floor
| higher and with less 'head'.

Completely conventional two header tanks, and indirect (coil) HW cylinder.
Two circuits, downstairs and upstairs which only gets used in very cold
weather

The only oddity is that it will work by gravity in power cuts, but as we
have had no long power cuts in 25 years, that is going.
--
Dave Fawthrop dave hyphenologist co uk
"Intelligent Design?" my knees say *not*.
"Intelligent Design?" my back says *not*.

In article ,
Dave Fawthrop wrote:
Completely conventional two header tanks, and indirect (coil) HW
cylinder. Two circuits, downstairs and upstairs which only gets used in
very cold weather

The only oddity is that it will work by gravity in power cuts, but as we
have had no long power cuts in 25 years, that is going.

Does this refer to the heating? It must be pretty old if there's no
electrics in the boiler. And if it works without the pump running this
will need sorting, as it will waste energy with the new boiler.

If you mean the hot water, no electricity is needed to access stored hot
water.

--
*If you're not part of the solution, you're part of the precipitate *

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 29 Aug 2005 09:02:43 +0100, "Dave Plowman (News)"
wrote:

| In article ,
| Dave Fawthrop wrote:
| Completely conventional two header tanks, and indirect (coil) HW
| cylinder. Two circuits, downstairs and upstairs which only gets used in
| very cold weather
|
| The only oddity is that it will work by gravity in power cuts, but as we
| have had no long power cuts in 25 years, that is going.
|
| Does this refer to the heating? It must be pretty old if there's no
| electrics in the boiler. And if it works without the pump running this
| will need sorting, as it will waste energy with the new boiler.

It uses a conventional controller with pump but could be switched to manual
in the case of another "Winter of Discontent" All that will be ditched
when a new boiler is installed.

--
Dave Fawthrop dave hyphenologist co uk
"Intelligent Design?" my knees say *not*.
"Intelligent Design?" my back says *not*.

In article ,
Dave Fawthrop wrote:
| Does this refer to the heating? It must be pretty old if there's no
| electrics in the boiler. And if it works without the pump running this
| will need sorting, as it will waste energy with the new boiler.

It uses a conventional controller with pump but could be switched to
manual in the case of another "Winter of Discontent"

Please explain?

--
*How many roads must a man travel down before he admits he is lost? *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Fawthrop wrote:

Objective is to save space.

Save space as it "loose the tanks etc" or really save sapace as in the
boiler needs to be tiny?

I have looked in Google Groups for old threads, and tried to answer
the questions which may be asked.

Kitchen tap gives 16l/m
Bath tap hot water gives 9l/min
Soft water.

I would start by downloading the free boiler database program:

http://www.sda.co.uk/qsedbuk.htm

That will give you the stats for most boilers.

As the others said you can pretty much ignore the heating side, however
it is worth looking for a model that will modulate as low as possible.
In a well insulated house however even a small boiler will cycle a bit
since it is not often going to be cold enough to keep above the minimum
modulation point.

Based on my experiance with my HE35, you may find something like the
Ideal Isar HE30 about right for your needs. It is physically very
compact, and will modulate down to 8kW. There is also the ECO Hometec
EC23s which will modulate right down to 4kW and still gives 28kW to DHW.

(personally I would not install anything smaller than about 35kW for
water heating though).

As I will now be pressurizing the central heating pipes (copper with
Yorkshire fittings) does anyone expect problems with this?

With the pipework no. With radiators, only if they are close to
knackered anyway. With very old lockshield valves - they may weep and
need replacing - but most won't.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Sun, 28 Aug 2005 12:26:22 +0100, Dave Fawthrop wrote:


I am thinking of replacing my conventional central heating and hot
water system with a gas combination boiler, for my four bedroom
extended semi, with one bathroom. My present system is 25 years old,
when I did the heating calculations and ended up with a 10kw boiler,
which works perfectly well with ample heat output, even in the coldest
weather. When I did the heating calcs, the house was *very* well
insulated, and I have continued adding insulation/double glazing over
the years, so it is now *extremely* well insulated. I am therefore
looking for a combi with less than 10kw output to central heating,
plus enough say 10l/m to the DHW.

Objective is to save space.

I have looked in Google Groups for old threads, and tried to answer
the questions which may be asked.

Kitchen tap gives 16l/m
Bath tap hot water gives 9l/min
Soft water.

Googleing for combination boilers only gives huge 20+kw models does
anyone here know of anything smaller?

As I will now be pressurizing the central heating pipes (copper with
Yorkshire fittings) does anyone expect problems with this?


The lowest gas rate I've seen is an 18kW Vaillant unit made around 15
years ago. This will provide an even more limited flow of HW than the
'standard' 24kW units.

It might work for a small dwelling with no bath.

--
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