On 12/03/2018 12:46, Roger Hayter wrote:
John Rumm wrote:

On 12/03/2018 11:25, Chris Hogg wrote:

We've just had a traditional sixty-year-old DHW system replaced by an
unvented, mains-pressure system in my late mother's bungalow, which we
intend to move into soon. Several comments:

It's based on a Joule tank, http://bit.ly/2Ht27Gz . The plumbing seems
a lot more complicated than before, with pressure regulators,
expansion vessels, pressure relief valves, tundishes etc all over the
place. The airing cupboard is now a cat's cradle of pipework. Whether
it could be simpler, I don't know.

Here is the basic layout you can expect:

http://wiki.diyfaq.org.uk/index.php/...nts_of_an_unve
nted_cylinder

I think it all has to be installed
by a specialist, rather than DIY, BIMBW.

Historically it was the case that only unvented cylinders were covered
by building regs (Part 3 document G). These days *all* cylinders are
covered by the building regs. See approved document G for more info.

They also need to be installed by someone who knows what they are doing!
(although that applies to any cylinder - unvented ones may be less well
understood by some plumbers).

Modern installs should also include things like mixing valves to limit
the maximum temperature at the point of use, but again that applies to
all stored water systems.

The DHW cylinder itself is much bigger that I expected; this may just
be what the plumber chose to install, rather than being necessary. My
comment to the plumber was that it looked like a section from a Saturn
5 rocket.

Yup unvented cylinders are often available in larger capacities than
traditional ones. (although you can still do the same trick doubling up
smaller cylinders like you can with a vented system to get more capacity)

Personally I fitted a 210L one which is probably about 5' tall. The
outer shell and integral insulation can make them look a bit more
"solid" than a normal tank. If I were doing it again, I might go for the
next size up.

A potential disadvantage is that in very cold weather, such as we've
just had and where the mains supply may be off for several days, is
that you have no water at all. At least in our present place when the
water was cut off for 36 hours, we could draw down the water from the
tank in the loft, boiled where appropriate, but that wouldn't be an
option with an unvented system unless some way was found of retaining
the tank, in which case why bother with an unvented system at all.

Sometimes upgrading the connection to the mains is way of solving a
number of related problems (lack of flow rate, freezing etc). A nice
32mm MDPE pipe buried deep enough ought not freeze and will make any
mains pressure water system work much better usually.

As a matter of interest, do you think that is likely to be worth doing
if the water board side connection is 2m of 25mm?

You mean using a larger pipe than theirs? It depends on the
circumstances... If you have say 40m of 1/2" pipe after that, Then any
increase will make a significant difference. The cost of the pipe is
usually only a small part of the overall cost of swapping it, so you may
as well over rather than under spec it.

(Flow resistance is a function of both diameter and length so a short
run of something narrower is not necessarily a show stopper)




--
Cheers,

John.

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