Heating on during the night does not use any more gas.

JohnSwift10

So something must be offsetting those differences.  Could it be that the boiler runs more efficiently, more of the time in condensing mode?

The temperature of the radiators is less at 08:00 when the thermostat is set at 18 deg C during the night than when it is set at 14 deg C.

In fact after the house achieves its temperature of 21 deg C the radiator temperatures are a few degrees less for the rest of the time the heating is on. 

Scot_39

Small differences in external night and day weather can make a big difference to consumption and so losses and required heat energy.

Sunny or cloudy, still or windy all factor in, not as simple as just absolute temperatures.

And even your own non heating energy use can make a difference too.

You generate an extra kWh or 2 by cooking for longer, ironing or whatever- that's energy your gch boiler doesn't need to add.


As can other things like having doors or windows open more frequently especially if for longer. 

And not just simply temperature - but wind direction and speed and hours of sunlight exposure all need to be considered.

It's easy to look at simplistic static losses in a lab style setup for a given set of conditions and relate to internal thermostat changes - but it's far more difficult to find consecutive days - especially at this time of year - when house use and outside climate impacts match.

But I believe the widest held view is that switching off or simply dropping thermostat overnight so boiler switches itself off will result in lower overall consumption on average.


"Edit

Which is why likes of energy savings trust recommends programmable heating times to match needs.

 https://energysavingtrust.org.uk/advice/thermostats-and-heating-controls/

JohnSwift10

QrizB  I live in Scotland and the temperature is a lot lower here than in Southampton.

Scot_39

JohnSwift10 said:

QrizB  I live in Scotland and the temperature is a lot lower here than in Southampton.

Yes around 3-4 C on temp, on average as well as different mixes rainy vs sunny and wind speeds too.

A classic example was weather on today's 6pm news - quoting Aberdeenshire -5C 
Cornwall 10C.

Qyburn

From a local weather station in Aberdeenshire ..
2nd Dec minimum  -7.7°C, average -5.0°C
3rd Dec minimum   -6.8°C, average -1.7°C
4th Dec minimum   -0.8°C, average  1.9°C

QrizB

JohnSwift10 said:

QrizB  I live in Scotland and the temperature is a lot lower here than in Southampton.

OK, the equivalent chart for Inverness airport is here.

• Dec 2nd - temperatures didn't rise above zero, was -4 until 1000 and again from 1600.
• Dec 3rd - a similar morning to te 2nd, but the afternoon was much warmer (tho' still freezing)
• Dec 4th - temps rose to 0C ar 4am then stayed above freezing pretty much all day

Again, 2nd was colder than 3rd which was colder than 4th.

Petriix

victor2 said:

THis reminds me of the long long thread that ran for about 10 years:

https://forums.moneysavingexpert.com/discussion/4327195/energy-myth-busting-is-it-cheaper-to-have-heating-on-all-day/p1

People tended to be divided into two camps. 

The two camps are: those who understand physics and those who don't. There are some very rare edge cases where calling for more heat at certain times could hypothetically result in less overall energy consumption, but these scenarios are such outliers that they aren't really worth considering.

The idea of attempting to compare day-to-day usage is flawed because there are far too many variables. Short of setting up two identical houses and controlling everything with absolute precision, there's simply no accurate way to measure the difference. 

As long as you have the flow temperature set correctly then you aren't going to be saving energy by having the heating on for longer.

Qyburn

QrizB said:

JohnSwift10 said:

QrizB  I live in Scotland and the temperature is a lot lower here than in Southampton.

Again, 2nd was colder than 3rd which was colder than 4th.

Looking at his gas consumption during those set back hours, from 23:30 to 07:45 then he used nothing on the 2nd or the 3rd. On the 4th, the warmest day, he used 0.483 kWh.

Focussing on the whole relevant period, from start of setback at 23:30 until the house was fully warmed back up, the usage was ..
2nd (overnight setting ??)      overnight         0kWh morning warm up 2.994kWh
3rd (overnight setting ??)       overnight         0kWh morning warm up 2.315kWh
4th (overnight setting 18°C)  overnight  0.483kWh morning warm up 2.529kWh

I don't see a correlation either with local temperature or with the overnight setting.