On Mon, 10 Jan 2005 10:10:47 +0000, Christian McArdle wrote:

We need more information about your expected water usage. In particular, we
need to know:

1. How many people live there?
2. How many teenage daughters? (better not publish your address though!)
3. Does anyone in the house prefer baths?
4. Does anyone like having long showers?
5. Are you likely to add an additional bathroom, in a loft
conversion/extension, say?
6. What is the maximum flow from your kitchen tap? (measure with bucket and
timer)
7. Is your electricity supply reliable?
8. Is cost a major factor?

There are several possible solutions. The answers to the above questions
will determine the best solution for you. Some possible suggestions a

1. Instantaneous combi. The cheapest solution will provide unlimited length
showers of good quality. Requires about 20lpm from the mains water supply.
Bath filling will be slow. Temperature regulation will be poor, but not a
problem if the shower mixer is chosen carefully. It will be the most energy
efficient, assuming similar boiler types.

2. Unvented cylinder. This will be the most expensive solution. It will
provide oodles of hot water at mains pressure, enough to drive the largest
and most obscene panel shower with body jets. It will require yearly
maintenance to ensure continued safety. It will fill a bath as rapidly as
the water can enter your house down the supply pipe.

3. Heat bank. This will cost a fraction less than the unvented cylinder.
Purchase costs are similar, but installation is simpler. It will also
provide mains pressure hot water, but flow rates might be slightly limited
if your mains water supply is really strong. It will still fill a bath in 3
minutes, so this isn't a problem. It is inherently safer than an unvented
cylinder, reducing the need for maintenance, but might be slightly less
energy efficient, as the condensing boiler may need to run at a higher
temperature. Some installers will not have heard of them, and so may refuse
to fit them. The hot water is never stored in this type of system, meaning
that the hot tap provides drinking water (unless you have a water softener).
This can be useful when filling kettles/saucepans, if you're not a patient
type.

4. Conventional gravity system. This will be cheaper than the mains pressure
options. It is a good system when the mains water supply is poor. When pump
assisted, it can provide excellent shower and bath filling performance, as
the expense of noise and pump maintenance implications. It requires a large
cold cistern in the loft, which can be problematic if it is decided to have
a loft conversion, or the loft space is not suitable for other reasons.

Some combi boilers work on the principle of (2) and (3) above, but with
small stores. They can be useful in some situations, particularly when space
is limited. However, they can be expensive, often more so than the full
sized discrete systems they emulate.


It's refreshing to see a good range of options listed with the strengths
and weaknesses listed instead of a one-size-fits all slanging match.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at 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