On 14 Jan 2004 02:29:08 -0800, (Danny) wrote:

So to answer my question, using the system that I have. Is it best to
switch off the central heating completely during the day, switching on
when I'm in the house, and also to have the immersion heater
(permanently isolating the CH circuit from the HW storage) coming on
for 1/2 hour in the morning and 1/2 at night.

Or should I leave my immesion completely off, turn down my system to
say 17 degrees when out of the house, and back up when in the house
(except at night!)

It really depends on the house and the controls in use.
It also depends on the hours of occupancy.

If you have a simple bimetal thermostat, for example, you can easily
get into a situation where the temperature massively overshoots if you
are warming from a lower starting temperature. If that is happening
as you are going out in the morning then you've wasted the heat. If
it happens during the evening, then you may well overheat the house
and make it uncomfortable.

The best, reasonably economic solution is to fit a
thermostat/programmer with optimised starting, different setback
temperatures at different times of the day.

You will then be able to set appropriate temperatures for the
different periods and the controller will take care of starting the
system at the right time to achieve them without significantly
overshooting and wasting energy.

You should certainly leave the immersion heater off except for
emergencies because the cost of energy is 3-4 times that of gas, so
even if you heat the water with gas non-optimally, it will cost less.

Whether you want to turn the gas heating of the hot water on and off
is up to you. If the cylinder is really well insulated, then it
doesn't make a great deal of difference as to whether gas heating of
it is enabled 24/7 if your usage is relatively high and at arbitrary
times during the 24 hour period. For example, in my case, hot water
could be used by somebody in the house more or less any time and the
cylinder is highly insulated. However, if you are a creature of
habit, then you may save energy by timing the gas heating of the water
for shorter periods to match your pattern of use.


..andy

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