Is this gas used about right?

Auti

Hello, got up this morning and was 14 degrees in living room (6 am) and was too cold for child so put gas central heating on - first time since last winter and has been recently serviced. Read the IHD kWh used so far before turning it on then had it on for 30 mins exactly then read the IHD again. Taking one amount from the other it showed that for half an hour it used 7.12 kWh - does this sound about right? for me it is a scary amount as it only raised temp to 16 degrees and this is not winter yet. I am wishing Eon Next would hurry up and put the new tariff onto my IHD as it is making it hard to work out cost (x 3 of old tariff) and I am cost controlled. I am also very scared about April increase and having enough money for next winter.

northernsoul

Typically, in the 1st hour you will use 3x the amount of gas than in each hour afterwards.
From 22/12/2021
My terraced house, outside temp -1C in morning to 3C in afternoon. Inside temp at start 14C , target temp 18C. Boiler set at 62C. Readings from gas meter.

07:00   14C
08:00.   17C.   1.01m3.  11.39kWh

09:00.   18C.   0.36m3
10:00.   18C.   0.35m3
11:00.    18C.   0.34m3
12:00.    18C.   0.31m3
13:00.    18C.   0.34m3
14:00.    18C.   0.27m3
15:00.    18C.   0.28m3
16:00.    18C.   0.28m3
17:00.    18C.   0.28m3
18:00.    18C.   0.25m3
19:00.     18C.  0.24m3
20:00.     18C.  0.23m3
21:00.    18C.   0.26m3

Total 07:00 to 21:00 54.13 kWh (I did not convert each hour to kWh just the accumulated amount each hour)
As you can see, once settled it uses about 0.3m3 per hour or 3.5kWh. So , once up to 18C it would use 84kWh per day (24*3.5) if you wanted it on 24 hours.

matelodave

You have to understand that when the heating comes on, the boiler winds up to full power until the house gets heated up to temperature at which time the room stat or boiler stat will then turn it on and off to maintain the set temperature and its consumption will reduce by quite a bit  

It could well take an hour or two at high power until the place has warmed up, depending on what sort of boiler, what sort of controls, how they are set and how cold the place was when you turn it on and how hot you want it to get. 

IMO you really need to understand how your heating works and what the IHD is telling you and as the IHD only gets info from the gas meter once every 30 minutes, it's never going to properly reflect what is going on. Electricity is much more accurate as its in virtually real time, but gas is always about half an hour behind. The only way to get instantaneous info is to read the gas meter itself and not the IHD, but even then, watching it ramp up won't really help you understand what is going on.

[Deleted User]

@matelodave is absolutely spot on. My 24kW boiler was on for 2 hours this morning to get the house up to 18C. The boiler flow temperature is set at 60C. Unused rooms are set to 13C. Total usage so far is 12.85kWh.

Your usage figure will depend on how many rooms you are trying to heat up and to what set temperatures, and the level of your home insulation. A room will only reach a set temperature when the heat entering the room equals the heat loss.

Auti

Thank you @matelodave I did not realise that my IHD could be half an hour behind what is really being used -it gets very complicated! I am trying to get a ball park figure/idea of costings so I can budget, sort of trying to standardise one variable whilst estimating the rest. I have a set amount per week so I am trying to use it wisely so that I can bank unused for the real winter otherwise  life could get very difficult and this is not of my child‘s making. Thank you for all your replies.

doodling

Hi,

It is important to understand that your central heating system goes through a number of different phases when turned on from cold.

1. When first turned on, the water in the central heating system will be cold and the boiler will run at full power until... 
2. The water in the central heating is up to temperature when the boiler (assuming that it is a vaguely modern one) will reduce its power output (and hence the amount of gas it uses) down to the level it needs to keep the water in the system at the correct temperature.  The boiler keeps running until...
3. The room(s) with thermostats in get up to temperature, at that point the boiler is turned off and stays off, until...
4. The room cools down again and the boiler is turned on.  At that point, you go back to (1), but you don't stay there very long before moving onto (2) as the water in the central heating system is already warm and you don't stay in (2) very long before moving onto (3) because the room is already warm.

Note that the length of time spent in (2) and (3) will depend on how cold it is outside which will determine how much heat is being lost from the room whilst you are trying to heat it and when it is up to temperature.

Because of the above, the only way to know how much your heating costs to run is to run it and measure the amount of gas used for a whole representative cycle - i.e. if you are going to only run the heating for an hour then run it for an hour and see how much gas is used, or if you are going to run it for 8 hours do that and see how much is used (it won't be 8x the usage for an hour).

Bear in mind that the cost will vary with the outside temperature (because your room cools down quicker and the boiler has to come on again sooner) - if you are keeping a room at 20C then it will use around twice as much gas to keep it that temperature if the external temperature is 0C compared to an external temperature of 10C (and three times as much as the 10C case if the outside temperature is -10C).

Auti

Thank you @doodling for a very clear explanation, it is appreciated. The gas boiler is 11 years old, an Ideal Icos, and serviced each year. Have thermostatic valves that are older than the boiler - Honeywell - and a thermostat in the hall set to 17 degrees C (it is a dial type so could be 16 - 18 degrees as not sure how accurate it is. I use the hall thermostat to control the boiler as the control box by the boiler is older than the boiler and does not give me the control/display that I need. Thank you again for your help.

doodling

Hi,

The Icos qualifies as a relatively modern boiler so that is fine.  I didn't want to confuse my explanation with too much detail but with older boilers, or if the boiler can't reduce its power output to a sufficiently low level then what happens during (2) is that the burner in the boiler turns off but the pump keeps running to circulate the water and the burner turns back on again when the water in the radiators cools down a little bit.  The Icos can't turn its burner down to very low levels - perhaps only down to 60% of its maximum so you might see that happening but it is nothing to worry about and doesn't have a big effect on cost.

The thermostatic values will be fine, even if they are old, there is nothing much in them to go wrong.  If they do fail then you will be able to spot it, either the radiator won't turn on at all or it will be stuck fully on, even with the valve turned down.

There is a debate to be had about where the best place to have a thermostat is.  They have historically been put in the hall because that has historically been the coldest place in the house and you don't want the boiler turning off until all the rooms (including the hall) have warmed up.  With a well insulated house with thermostatic valves, positioning the thermostat in the most used room can be a better choice as that is where you actually want to be comfortable.

Hopefully the control box has a timer so you can set the heating and hot water to come on at the times you want, if it doesn't then that is recommended.

macman

With the CH running at full bore from cold start first thing in the morning, a usage of about 14kWh per hour is not exceptionally high. Once it reaches the set temp of 17C it will modulate back to a much lower burn rate.
If you are paying 91p for that half hour usage, remember that your monthly rebate alone of £66 will give you about £2.20 per day extra contribution to your billing, and the £150 CT rebate another 50p per day.

shiraz99

So to the much discussed debate, is it currently cheaper to keep the heating on all day, ticking over at 18C rather than having a big start up in the mornings and evenings?

Miser1964

shiraz99 said:

So to the much discussed debate, is it currently cheaper to keep the heating on all day, ticking over at 18C rather than having a big start up in the mornings and evenings?

Depends on so many factors, although I'd say 18°C is a touch on the high side for a 'setback' temp; I use 15°C.

BUT I've also optimised as far as possible the CH setup by range rating the boiler, dropped the flow temp to 55°C and have a Nest thermostat which 'knows' the outside temp to modulate the calls for heat to avoid over-shooting. Full weather compensation would be best, but the Worcester Bosch doesn't use standard OpenTherm