"Andy Hall" wrote in message
news
On Mon, 11 Oct 2004 19:21:37 GMT, "John Orrett"
wrote:

Hi all; my wife has advised me that we are getting a new bathroom suite!
she
would like one that has the taps in the wall rather than on the bath
itself.
The shop told her that we cannot do this at present as we only have a
Gloworm Ultimate 50 boiler and an immersion heater, and not a combi.
Couple of questions that I would like some help with please.

1. Does a combi need any more ventilation space around it or external
venting than the present boiler (which is situated in the kitchen behind
a
false cupboard door)?

It depends on the boiler and manufacturer. Most manufacturers have
this info. on their web site if you look in the installer section.
Don't forget about possible flue space.


2. Can I run the central heating via a combi?

Yes you can.

3. Cost wise, will a combi work out more cost effective than the current
boiler/immersion setup?

In running cost terms, yes, if you are using only electricity to heat
the water at the moment.


4. How much should I be paying for a decent combi, and any
recommendations
on make and model etc?

Good ones are in the £800-1100 bracket.


My wife likes lots of baths, so the immersion is on quite a lot, and
obviously the central heating is now on a fair bit. To give an idea on
costs, our electric bill per month is £52 and the gas is £36. I am in the
process of swapping from British Gas for both to Powergen, saving £200
per
annum, but that's another story :-).
Any help appreciated,

Before you do anything else, check the water flow rate at the kitchen
cold tap using a stop watch and a bucket. If the rate is less than
about 15-20 litres/minute, using any kind of mains fed hot water may
be disappointing.

Smaller combi boilers are quite limited on hot water production rate.
It can be as little as 9 litres/min, with better ones achieving
15-18lpm. bear in mind that this is for a 35 degree rise in
temperature, so in the winter will represent the total rate at bath
water temperature.
Normally a tank/cylinder based system will fill a bath very quickly,
so as another test, using a bath tap adjusted to the rate of the
intended boiler, time how long it takes to fill the bath.
Smaller combis can take 15 minutes easily, so certainly ask your wife
whether that is acceptable.

Another option would be to keep the existing boiler and heat the
cylinder from it. This would be cheaper to run than the immersion and
much faster to re-heat. You may need to replace the cylinder, but it
would be cheaper than a new boiler.


View two combi boilers. One doing one zone of space heating (upstairs) the
other doing another (downstairs). Each boiler will have a programmer/stat
for each zone, preferably a Honeywell CM67, or equiv. Combine the DHW
outlets just before the bath using non-return valves and a small shock
arrestor expansion vessel, as per Worcester-Bosch Tech dept. It will fill a
bath pronto and give good power showers for two showers.

With combi's the most important figure is the flowrate. 11 litres/min is
fine for showes and the odd slow filling bath. Here is a recent post of
mine...


For an even better flow rate and cheap too for what you get, assess using
two Worcester-Bosch Junior combi's.

For high flowrates it is cost effective to use two Juniors and combine the
DHW outlets. Worcester-Bosch will supply a drawing on how to do it, or ask
me here. Two Juniors are available for around £1000 to £1100 depending on
what sized units you buy. They have 24 and 28 kW models, you could one 24kW
and one 28 kW. That is cheaper than the Worcester HighFlow 18 litres/min
floor mounted combi and can deliver about 21.5 litres/min @ 35 degree temp
rise and never run out of hot water. The highest flowrates of any
infinitely continuous combi is 22 litres/min @ 30 litre/min temp rise, which
is the ECO-Hometec which costs near £2K.

Have one combi do the downstairs heating on its own programmer/timer
(Honeywell CM67 or equiv) and one do upstairs. No complex and space
consuming zone valves used. Natural zoning, so you don't have to heat
upstairs when you are not up there saving fuel. The running cost will be
approx the same as a condensing boiler heating the whole house. No external
zone valves either, and simple wiring up too. The Juniors are simple and
don't even have internal 3-way valves.

If having two showers, have the shower split between the combi's to reduce
influence from one to the other.

Also if one goes down you will have another combi to give some heat in the
house and DHW too. Combine the outlets for the DHW bath pipes and all the
baths you want very quickly and no waiting. Best have the showers on
separate combi's.

Do not exceed the gas meter flowrate of 212 cu foot per hour. To calulate,
e.g., a boiler is 100,000 BTU/hr "input". Divide by 1000 giving 100 cu foot
per hour. Add up all the appliances.

The Juniors are not condensing combi's, yet overall heating costs will be
equivalent to one condensing boiler as the upstairs will not be heated most
of the time.

A win, win, situation.

Its advantages a

- cheap to install.
- quick to install.
- space saving (releases an airing cupboard). Both can go in the loft, or
at the back of the existing airing cupboard.
- never without heat in the house as two boioers are used.
- high flowrates (will do two showers and fill a bath in few minutes),
- No waiting for a cylinder to re-heat
- Natural zoning, one does upstairs and one does down
- hardly any electrical control work (running a wire to a programmers/stat
and power to each,
- simple no brainer installation,
- minimal components used.
- less piping used
- cheap to run overall as upstairs would be off most of the time
- etc.