"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Danny wrote:

Hi all,

I've a couple of questions that I was hoping someone could help me out
with.

I currently leave my central heating system on - constantly (during
winter). When I'm out of the house I turn the room thermostat down to
20 degrees, when I return I pop it back up to 22-23 degrees, at night
I put the system back down to 20 degrees.

My theory is that because the water (in the system) is actually
already at temperature and the house never goes below 20 degrees and
that this is a more efficient way to heat my house and keep the bills
down. When the room thermostat is not calling for heat the boiler
only comes on every now and then for approx 30 seconds, I assume just
to keep the water which flows through the HW cylinder at the required
temp.

Would anyone agree with this?

This question may seem silly but if my central heating system is
switched off all day the house temp drops to approx 15-16 degrees,
this takes quite some time to get to 22-23 degrees and I guess alot of
gas also!

Also, if the above holds true, would it be more economical if I close
the valve to the HW cylinder and just use the electric immersion
heater and a timer for the required hot water?


Thanks in advance


If your system is wired correctly, it should *never* come just to keep the
boiler hot - unless either the room stat or cylinder stat is calling for
heat.

According to the instructions for my Danfoss TP9 Programmable Timer/Thermostat..
if you have a gravity hot water system and pumped central heating you may well
not have
a H/W tank thermostat. Basically the boiler operates as you describe.


If you have Honeywell C plan then the boiler would only function when either the
C/H or H/W require.


http://content.honeywell.com/uk/home...20C%20Plan.pdf


One advantage of the TP9 is that it only supplies power to the boiler when
either the C/H pump is on
or the H/W timer is on.

With a conventional programmer the boiler is trying to keep itself warm whenever
the timer says the C/H is on which in your case would be always.

The other advantage of the TP9 is that you can make the C/H follow a temperature
profile with 6 changes per day. - different at weekends if you want.

The heating system has to replace the heat lost through the walls, ,
windows, roof and floor. The hotter the building, the greater the heat loss.
It is always more efficient to allow the building to cool down when you
don't need it to be hot - but better still if you have very good insulation
so that it only cools very slowly when the heating is off.

It is *never* more efficient (cost-wise rather than energy-wise) to heat
water with an on-peak electric immersion heater rather than by gas.

When I was a school I recall 'rate of loss of heat is proportional to the excess
temperature'. i.e. the warmer your house is compared to its surroundings, the
more heat it will loose.

The problem in practice is that can take a while for the house to heat up and
cool down - as you mention!.

Michael Chare