riccip wrote:
"Dave Plowman (News)" wrote:

And therein lies the problem. Using your boiler just to heat HW
alone is a bit like putting a V8 engine into a moped.

what exactly is the problem? I'm not seeing one.


That's why
combi-boilers were invented (although personally I hate the
wretched things!).

An immersion heater is 100% efficient from the moment it switches
on

yes, but thats not the whole picture. but its downsides normally
outweigh the upside.


and requires minimal energy to maintain optimum water
temperature. A gas boiler can be as low as 50% efficient when
heating just the copper cylinder.

please tell us which new gas boiler is 50% efficient. And when and why
one would heat just a copper cylinder.


The system has a warm up period
where no heat is being transferred.

yup, same for immersions. Measured in seconds in both cases.


Much of the heat produced by
burning gas disappears up the flue

well, 5 - 10%


and more is lost from the
pipework runs to the HW cylinder, often positioned some distance
from the boiler.

very little.


It's not that simple an equation. A boiler works hardest when
warming the house from cold. Once the desired temperature has
been reached an efficient CH system with TRVs burns considerably
less gas maintaining those temperatures.

ok

So the sooner desired
room temperatures are reached the better and more economical.

not quite that simple


Therefore if the HW cylinder has already been heated on Economy 7
the boiler will more rapidly heat the house.

it makes no difference whether the HW is heated before or after the
morning house heat up. Only when its heated during, which some systems
do permit, will it make any difference to heat up speed. But its really
no big issue.


Ask amongst your friends and you will be surprised at the number
of people who leave the boiler on all day to keep the water hot.
Even if it's timed for an hour it will begin to cycle according
to the boiler's stat, thus wasting an incredible amount of gas.

why is it incredible?


As HW is used, even a minimal amount, the boiler works hard to
reheat that portion of the cylinder.

you mean the same as an immersion does?


And if you left an immersion on all the time it would cost even more.

Certainly on peak-time electricity it would. However peak
electricity shouldn't necessarily be considered taboo. Take an
electric shower for example. Heavy on electricity but only for a
few minutes, offering considerable savings over a gas heated
shower arrangement.

Just how is 100% efficient 7p/unit electric heating cheaper than 90%
efficient 2p/unit heating?


NT