dennis@home wrote:



"Dave Baker" wrote in message
...

8

However with a reasonably well insulated house the net extra cost is very
low. If we assume in cold weather an 18 degree C difference between
inside and outside when the heat is on, 16 hours of heat on during the
day and 8 with it off overnight and a 4 degree total drop in temp of the
house overnight (i.e. an average of 2 degrees) the net extra cost of
keeping the heating on all the time is only about 4%. That's less than
you'd save just turning the thermostat temperature down by 1 degree.


Sorry but that does not make sense.
If its off for 8 hours out of 24 you will save nearly one third.
You may save more as it usually colder at night and will use more energy
than in the day.
It will take slightly more energy to raise the temp back to the norm in
the morning but it shouldn't take much.

I agree with your sound logic, in theory the heat losses (and hence energy
costs) through the night will be higher if the house is heated but a recent
check on meter readings suggest that the case might not be quite so
straightforward.

We have the heating set to run from 08:00 to 23:30. The overnight set point
is 13C so it's effectively turned off overnight unless the weather gets
very cold. The programmer uses optimum start so I don't know exactly what
time it normally starts up but the maximum advance is 2 hours so I'll
assume it starts up on average a bit less than this at 06:30 (I certainly
don't intend waking up at 06:00 to find out). Average gas consumption for
the last week has been about 300 ft^3 per day but extra meter readings last
thing at night and at about 08:00 for a couple of nights show that about
100 ft^3 are consumed each morning in bringing the house back up to
temperature leaving 200ft^3 for the remaining 15.5 hours, i.e. 200/15.5 =
12.9 ft^3 per hour to maintain a steady temperature. So if we left the
heating on all the time the daily consumption would be 12.9x24 = 309.6
ft^3 - remarkably close to what we're using already.

O.K. the losses through the night would be a bit higher due to the outside
temperature being lower but I don't expect it would make a huge difference.
I don't intend to put it to the test though because we don't like sleeping
in a hot bedroom but don't want to turn the bedroom TRV down because we
want the room to have warmed up by the time we have to get up in the
morning.

--
Mike Clarke