I have read as many FAQs, previous threads etc as i can find, and learnt
quite a lot, but would still appreciate advice if anyone can spare it.

I live in a 100 year old semi-d house, with existing conventional
floor-mounted boiler (approx 18 years old), open vented central heating
with a mixture of radiator types, hot water from cylinder, and a pumped
shower. I intend to get rid of most of it, and install a new condensing
combi boiler in the cellar, convert the central heating to a sealed
system (keeping about half the radiators, replacing / relocating the
rest), and convert the hot water to mains pressure (get rid of the
shower pump and cylinder etc). There's one bath, one shower and one
kitchen sink, with only one likely to be in use at any given time.

The work will be done by an installer (so this isn't really d-i-y) but
I'm planning to specify a Worcester Greenstar 35CDi combi boiler,
Honeywell CM67 programmable digistat (probably the wireless one, so that
I can experiment with locations), Myson (round-top) rads to match the
retained ones already installed, ? TRVs. I've calculated the required
radiator sizes using an old copy of Myson Heatloss Manager (Myson don't
seem to have this on their website any more, which is a shame).

I would be grateful for any reassurance that this all sounds reasonably
sensible, but in particular:
1) With condensing boilers is it still important to get the 'right' size
or might there be benefit in over-sizing a little?
2) Any problems using a Honeywell digistat with a worcester boiler?
There seem to be other similar products (eg Danfoss) - are there
significant differences? Surpisingly the manufacturer's websites don't
seem to give clear details. What we need is 7-day control, with the
ability to over-ride for periods, both for days (holiday) and hours
(during the day), without having to re-programme.
3) Controls generally... I've seen a number of threads about the wisdom
or otherwise of a traditional room thermostat in the hall, no TRV on the
radiator etc. (I think) I understand the requirement to achieve 'boiler
interlock' by one means or other. However I wondered if anyone has
knowledge or experience of more 'hi-tech' solutions, eg Honeywell
CM-Zone? Also, any preferences for TRV manufacturer?

Sorry about the length of the post. Any comments would be much
appreciated.
--
Rick Bowlby

Use Reply-To for reply

On Sun, 08 Jan 2006 10:55:03 +0000, Rick Bowlby wrote:

On Sat, 7 Jan 2006 at 20:17:12, Ed Sirett
wrote:
On Sat, 07 Jan 2006 12:14:49 +0000, Rick Bowlby wrote:

1) With condensing boilers is it still important to get the 'right' size
or might there be benefit in over-sizing a little?

1) Yes, see BoilerChoice FAQ (this is quite new so you may have missed it).

Which is 'yes'?! Actually I had read the FAQ, which was helpful -
"Modern boilers can adjust their output power over a range
automatically, therefore over-sizing is less of a sin that it used to
be, nevertheless getting this right will save some gas". However I do
want to ensure that there is a decent HW flow rate. Heatloss manager
reckons I need a 25kW boiler for heating, so I was thinking of going up
to 30-35 to be on the safe side with HW.

Seriously. That's a gross over estimate of the HW requirements when
combined with a cylinder/thermal store. You'd only need that sort of HW
if you have a stack of people (12+) people living at your place.

28-30kW (load of models around that size) would be quite enough.

However you should allow 40 litres of stored HW/person.


--
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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Sun, 8 Jan 2006 at 23:45:29, Ed Sirett
wrote:
On Sun, 08 Jan 2006 10:55:03 +0000, Rick Bowlby wrote:

On Sat, 7 Jan 2006 at 20:17:12, Ed Sirett
wrote:
On Sat, 07 Jan 2006 12:14:49 +0000, Rick Bowlby wrote:

1) With condensing boilers is it still important to get the 'right' size
or might there be benefit in over-sizing a little?

1) Yes, see BoilerChoice FAQ (this is quite new so you may have missed it).

Which is 'yes'?! Actually I had read the FAQ, which was helpful -
"Modern boilers can adjust their output power over a range
automatically, therefore over-sizing is less of a sin that it used to
be, nevertheless getting this right will save some gas". However I do
want to ensure that there is a decent HW flow rate. Heatloss manager
reckons I need a 25kW boiler for heating, so I was thinking of going up
to 30-35 to be on the safe side with HW.

Seriously. That's a gross over estimate of the HW requirements when
combined with a cylinder/thermal store. You'd only need that sort of HW
if you have a stack of people (12+) people living at your place.

28-30kW (load of models around that size) would be quite enough.

However you should allow 40 litres of stored HW/person.

But I want to get a combi boiler and mains pressure HW, does that make
any difference?
--
Rick Bowlby

On Mon, 9 Jan 2006 at 22:25:05, Ed Sirett
wrote:

Just get the biggest combi you can afford to install.
Thewre seem to be a cluster of premium models around the 33-37kW mark as
opposed to the 24k or 28kW more basic models.

There are some combis which have substantial stores of HW built in these
units may suit your requirements better.

Thanks, that's useful.

Are there any sites (eg retailers) where you can compare boiler
features?
--
Rick Bowlby

On Mon, 9 Jan 2006 22:54:49 +0000 Rick Bowlby wrote :
Are there any sites (eg retailers) where you can compare boiler
features?

Our free QSEDBUK program will let you select boilers with particular
output, fixing position etc. There are other factors which are harder
to categorise: for example in our church the Keston Celsius is
particularly suitable because of the fluing options and being able to
remote wire the panel run/fail lights back to a visible position.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]