Just need to check my workings out.

JamesFews

Hi All,

I tried to use an online calculator to work out what my electric boiler is using....it came back with £230 a month just for heating so I thought nope, thats not right. So i worked out how to do it the manual way and I just want to get some more eyes on my workings out. So...

14.4Kw Boiler
Only on between off peak Economy 10 hours which is 7 hours @ 7.17pKwh
Only doing central heating, not water.

So

14.4kW x 7 = 100.8kW
100.8kW / 1000 = 0.10
0.10 x 7.17p = 0.72p
0.72p x 365 = £263.79 Per Year
263.79 / 12 = £21.98 Per Month

Do those workings out look right?

Thanks people!

matelodave

JamesFews wrote: »

Hi All,

I tried to use an online calculator to work out what my electric boiler is using....it came back with £230 a month just for heating so I thought nope, thats not right. So i worked out how to do it the manual way and I just want to get some more eyes on my workings out. So...

Yes it was

14.4Kw Boiler
Only on between off peak Economy 10 hours which is 7 hours @ 7.17pKwh
Only doing central heating, not water.

So

14.4kW x 7 = 100.8kW - Correct

100.8kW / 1000 = 0.10 - wrong - what is this for

0.10 x 7.17p = 0.72p - wrong - should be 100.8 x 7.17 = £7.23

0.72p x 365 = £263.79 Per Year - wrong, should be £7.2 x 365 = £2638.95

263.79 / 12 = £21.98 Per Month - wrong should be £2638.95/12 = £219.81

Do those workings out look right? No, see the corrections

Thanks people!

look at the corrections - it's unlikely that the boiler will take a whole 100.8kwh in a night if its got a thermostat, likewise if it's for heating then it shouldn't be on for 365 nights a year either

JamesFews

I made an error in the format of the cost... please see correction in red.


Can you see again please

14.4kW x 7 = 100.8kW

100.8kW / 1000 = 0.10

0.10 x 0.17p = 0.72p

0.72p x 365 = £263.79 Per Year

263.79 / 12 = £21.98 Per Month

This is taking into account if I had it on for the whole year. I know I wont, but it helps me work out what the monthly cost is.
Thats using this website to work out the cost and conversion step by step.

https://www.saveonenergy.com/energy-consumption/

Thanks
James

MikeWhite

JamesFews wrote: »

I made an error in the format of the cost... please see correction in red.


Can you see again please

14.4kW x 7 = 100.8kW

100.8kW / 1000 = 0.10

0.10 x 0.17p = 0.72p

0.72p x 365 = £263.79 Per Year

263.79 / 12 = £21.98 Per Month

This is taking into account if I had it on for the whole year. I know I wont, but it helps me work out what the monthly cost is.
Thats using this website to work out the cost and conversion step by step.

https://www.saveonenergy.com/energy-consumption/

Thanks
James

Still looks totally incorrect to me!

One day of boiler use, assuming always on for 7 hours (which I guess it won't be but useful as a "worse case"):
7 hours times 14.4kw = 100Kwh per day!!!
7.17p times 100 = £7.17 per day.
For a month that is £215.

matelodave

why are you dividing 100.8 by 1000?

and what is the line 0.1 x 0.17 for.

If your heater is 14.4kw and is on for 7 hours it will consume 100.8kwh

If you pay 7.17p a kwh (thats £0.0717) then 100.8 x 0.0717 = £7.23

£7.23 x 365 = £2638.95/yr, divide by 12 = £219.91/mo

Your dividing by 1000 is giving you the wrong result, why are you doing it

another way of doing it is

100.8 kwh x 365 = 36,792kwh x £0.0717 = £2637.99/12 = £219.83

The slight difference is due to rounding errors but it still ends up as around £220/month not £22 a month

HogMan

As matelodave says in post 2, it is likely your assumption that the heating will be on at full blast all year around is incorrect rather than the method of calculation.

*j*

To find the daily usage why not take meter readings at about the same time each day and see what they show?

SpotlandRules

The dividing by 1000 is converting watts to kWh. But your first line

14.4kW x 7 = 100.8kW

already gives you kWh, so this is not needed.

EG, if I leave a 100 watt light bulb on for 7 hours, then this uses

100 * 7 = 700 watts

Convert to kWh
700 / 1000 = 0.7 kWh

System

JamesFews wrote: »

14.4Kw Boiler
Only on between off peak Economy 10 hours which is 7 hours @ 7.17pKwh
Only doing central heating, not water.

This is the bit that people are struggling with. I assume that you have electric wet central heating? Such systems can draw power for 7 hours a night BUT the actual power requirement will depend on how much heat has been used during the course of the day. To re-heat the water storage you may well need the full 7 hours today (as it is -6C outside as I type) but I doubt that you will need anywhere near that amount on a mild Winter Day.

The way that you are looking at the problem is similar to I have a 3kW kettle; how much will it cost me to run it continuously for 7 hours a day?

As others have intimated. Take a meter reading today and check it again tomorrow and note the kWh difference. Multiply that by 31 which will give you an idea of what it costs in a Winter month. Multiply that by 5 for the Winter months which will give you the total kWhs consumed. You can then do the unit price calculation to work out a rough Winter cost.

JamesFews

Ok thanks Hengus,

I will give that way a go.

Thanks all for your replies.


Regards
James

victor2

JamesFews wrote: »

Ok thanks Hengus, though it may prove a little difficult getting a reading at the start of the day as the heating comes on at 4 in the morning for an hour as that is a low rate time.

Regards
James

Doesn't matter. Presumably your meter gives two readings, a "day" rate and "night" figure.
Take both readings at the same time each day/week to get an idea what you are using, and do the necessary arithmetic to convert each to the cost for that rate. Add the two values together and away you go...