"Christian McArdle" wrote in message . net...
OK. It looks like a non-storage combi will probably not be suitable.
I measured the flow rate of the existing hot water and it's 16.5
litres per minute. The only combi I can find that comes close to this
is the W-B Greenstar 40 HE Plus which claims a 16L/min flow rate (but I
guess the
water would be colder than ours).

Yes, the combi flow rate will be at delta 35 or so. Your old hot water
system is probably on delta 55, so is equivalent to a combi flow rate of 26
litres per minute during winter. During summer, the difference would be less
stark, as the storage system will work as before, whilst the combi will
perform better.

All the plumbers I have contacted only want to fit combi boilers though.

One suggested a vented tank in the roof or a storage combi in the garage.
However the garage may not be built until April next and I know the building
regs are changing and the boiler we would fit would not be condensing.

BTW: Why are vented tanks so unpopular now?

Even combi fanatic could install a DPS Pandora. Explain that all it requires
is cold mains in, hot mains out and standard S-Plan controls to the boiler.
It is much simpler to fit than an old gravity based hot water system.

I'm not sure how I can measure the flow rate of the mains. There's
only two taps connected directly to the supply and their both small.

Measure from these anyway. If even the small taps can provide enough, then
you're laughing. Less than 20 lpm, get worried. 20-30 lpm, OK. 30+, good.
40+, excellent. If you have a garden tap, try that, too.

No garden tap but I'll try to measure the flow rate from the two cold taps
tonight. Incidently another plumber came around yesterday and said that
our flow rate in unlikely to suit an unvented cylinder because we have a
1/2" main (he didn't look at it though, but he does know the area).
I'm not doubting his word, but it has left me even more confused.

Is there a FAQ for the pros and cons of unvented cylinders?

There must be somewhere, however, from the top of my head:

Heatbank:
1. Much more simple to install.
2. Fundametally safer due to no storage of pressurised hot water.
3. Lower ongoing maintenance (no safety controls or bubbles to check
annually)
4. Doesn't require certification to be installed professionally.
5. Produces drinking water (assuming no water treatment required).
6. Integral TMV ensures constant DHW temp (some unvented will have this,
too)
7. Potentially faster recovery.
8. Can be fitted without an overflow (useful when no external wall)

Would a heat bank be inefficient if we only use hot water sporadically?
i.e. very little is used during the day in the week, but loads in the
evening? (I would have thought it would take a lot of energy to keep the
heat bank up to temperature).

Unvented cylinder:
1. More commonly available.
2. Higher potential flow rate.

Why would an unvented cylinder give a higher flow rate? Aren't they
both limited by the mains water flow?

M