Combi Boiler Gas consumption

rabbitmumu

Dear all

After receiving a shocking bill from Npower since I moved into my current property last christmas, this winter I have switched my combi boiler off manually during day time and have it on again in the evening and throughout the night.

Probably they are stupid questions but hope someone can explain this to me. Many thanks

Question 1: according to the manual, my boiler consumes 8.7-24 KW and it's a fairly new boiler. But according to SEDBUK it consumes 130w when there's elec power firing and 6w when not. Are they referring to gas and electricity respectively or are they both gas measurements? Why are they different?

Question 2: While checking my gas meter reading, I use about 0.5 -0.6 a day since December which is equivalent to around 16-19 Kwh per day.

If the guide of 8.7-24KW is right, and I switch on the gas for about 3 hours a day (allowing for temp control?) and 5 mins for a shower, how come I only manage to use 16-19Kwh per day? Or have I not done my maths correctly or allow for the correct kwh/kw?

Coz' I presume at least an hour a day I would have used 24KW when the boiler is on initially?

Many thanks

notbritishgas

rabbitmumu wrote: »

Dear all

After receiving a shocking bill from Npower since I moved into my current property last christmas, this winter I have switched my combi boiler off manually during day time and have it on again in the evening and throughout the night.

Probably they are stupid questions but hope someone can explain this to me. Many thanks

Question 1: according to the manual, my boiler consumes 8.7-24 KW and it's a fairly new boiler. But according to SEDBUK it consumes 130w when there's elec power firing and 6w when not. Are they referring to gas and electricity respectively or are they both gas measurements? Why are they different?

Question 2: While checking my gas meter reading, I use about 0.5 -0.6 a day since December which is equivalent to around 16-19 Kwh per day.

If the guide of 8.7-24KW is right, and I switch on the gas for about 3 hours a day (allowing for temp control?) and 5 mins for a shower, how come I only manage to use 16-19Kwh per day? Or have I not done my maths correctly or allow for the correct kwh/kw?

Coz' I presume at least an hour a day I would have used 24KW when the boiler is on initially?

Many thanks

The 8-24 kw is the gas figure, the gas consumed will actually be higher because those figures are for the output and as your boiler will only be about 90% efficient then the input will be about 10% higher.
The 130w and 6w are the electric usage when in idle state (6w) and when the ignition is firing up (130w).
Your usage of 16-19kwh per day is unbelievably low if you are using it all evening and throughout the night, some 12 hours? although I see you mention 3 hours, a bit confused by that. Are you sure your figure of 0.5-0.6 units (imperial I presume) is correct.

rabbitmumu

Hi Notbritishgas

Many thanks for your reply and solving question 1. Re question 2 - yes i agree it's unbelievably low too. 0.6 units on the meter is correct and use that long equation on my bill i.e. 0.6*31.55 = just under 19kwh. Does that look correct?

I switch on the boiler manually say from 8 o'clock in the evening when i return from work all the way until around 8am - but then the thermometer is only on 10-11pm at 17.5C, then throughout the night at 15C which I think the radiators maybe on from time to time because the flat is "quite" warm (ok...it's still cold at 15C) , then at 7-8am it sets to 16.5C when the radiators do come on again. So i am guessing at most the radiator will be on its full power for about 2 hours per day + another hour not in full power?

Now you are saying i will need add another 10% on the 8-24kw..... then it's even lower .... is there a chance that my combi boiler is so "efficient" that it only uses say 10kw per hour even when the radiator is fully on? Or have I missed out anything ? Many thanks again for your help

Cardew

The 130w will be for the electricity, including presumably the pump.

As stated above, 16-19kWh a day(50p to 60p) cannot be correct.

As your meter must be Imperial(cubic feet) to use only 0.5 - 0.6 gas units, are you sure you are reading the meter correctly?

The dial meter has pointers going clockwise and anti-clockwise.

rabbitmumu

hiya both - yes mine is an imperial one with a "ft^3" at the end... so reading x 31.55 = kwh. Is that correct?

because of the bill from last year, i am now ridiculously paranoid and read my meter from time to time. I have only started switching my radiators on since 27th Nov and before that only on for 5 mins shower everyday.

19/11/2010 = 7825
1/12/2010 = 7830
10/12/2010=7835
19/12/2010=7839
24/12/2010=7843

So on average I use 0.5-0.6 a day? Have I missed out anything? Thanks again

northernsoul

from 20/11 to today 24/12 on a imperial meter i used 105 units. From when i came home today when i turned the thermostat up to 22C (house was about 11C- no heating on since 6:30am) and for approx 8 hours until 10:15 i used 3 units. to use 0.6 a day is very very low! I have for the last 2 years had a Valiant 837 and before that i had a inefficient back boiler, but it has not used any less gas, although it has been colder

notbritishgas

rabbitmumu wrote: »

Hi Notbritishgas

Many thanks for your reply and solving question 1. Re question 2 - yes i agree it's unbelievably low too. 0.6 units on the meter is correct and use that long equation on my bill i.e. 0.6*31.55 = just under 19kwh. Does that look correct?

I switch on the boiler manually say from 8 o'clock in the evening when i return from work all the way until around 8am - but then the thermometer is only on 10-11pm at 17.5C, then throughout the night at 15C which I think the radiators maybe on from time to time because the flat is "quite" warm (ok...it's still cold at 15C) , then at 7-8am it sets to 16.5C when the radiators do come on again. So i am guessing at most the radiator will be on its full power for about 2 hours per day + another hour not in full power?

Now you are saying i will need add another 10% on the 8-24kw..... then it's even lower .... is there a chance that my combi boiler is so "efficient" that it only uses say 10kw per hour even when the radiator is fully on? Or have I missed out anything ? Many thanks again for your help

A Merry Christmas to you.
The figures of 8-24kw on your boiler are the low to high settings on the boiler. You will have a temperature dial on the boiler somewhere, it may have numbers 1-5 or similar or just a variable arrow, whatever, the lowest setting will be 8kw and the highest 24 kw so check what yours is set to. Your boiler will not be more efficient than 90-95%.
The boiler will be working hardest when it is first switched on and trying to bring the flat up to the required temperature, even then when the return water temperature reaches the set figure the boiler will start to modulate and use a minimal amount of gas.
You do seem to have done your working out correctly and from your later post with meter readings they do seem to correspond to an imperial meter. However in just over a month you have used 18 units, during this cold weather I am using 24 imperial units per week, but with the heating on much longer than you.
To sum up, you do not have your thermostat set very high so must have a nice warm flat anyway. I still find it unusual to only use 19kwh per day but enjoy it.
Just as an additional check take your meter readings daily, I realise over Christmas you may be home more than normal so may have to carry on for longer but even figures now may give some idea when related to the time the heating has been on.

Cardew

rabbitmumu wrote: »

hiya both - yes mine is an imperial one with a "ft^3" at the end... so reading x 31.55 = kwh. Is that correct?

because of the bill from last year, i am now ridiculously paranoid and read my meter from time to time. I have only started switching my radiators on since 27th Nov and before that only on for 5 mins shower everyday.

19/11/2010 = 7825
1/12/2010 = 7830
10/12/2010=7835
19/12/2010=7839
24/12/2010=7843

So on average I use 0.5-0.6 a day? Have I missed out anything? Thanks again

But have you read your meter correctly(assuming it is a dial meter). People assume the pointers all go clockwise - which they don't.

http://www.edfenergy.com/products-services/for-your-home/my-account/how-to-read-your-gas-meter.shtml

You don't say if your property is house or flat - but if the latter are you reading your meter?

One thing is certain, you are using more gas that 16kWh to 19kWh a day. 5 weeks in just about the coldest winter on record for heating and hot water for approx £18 is not possible!

Either a faulty meter or as above suggested errors.

rabbitmumu

Hi both - Merry Christmas to you both!! I have just finished putting the turkey in the oven and glad to receive replies from you both

Thanks for all your suggestions and advice.

I live in a mid-level 2 bedroom flat and it's South-East facing - so we get lots of sun (if there's any) probably 10-14 hours a day. At this moment the room temperature is 14.5C so I just put on a jumper and don't switch on the radiators.

SHOCKING!! over 100 units for a month is more than what i have used in last year (Dec 09 to Nov 10)! I guess living in a house is totally different to living in a flat. My meter is the top one on the link.

In terms of the boiler, we have a Vailliant 831and the Homecare guy checked it 2 months ago saying we put the dial incorrectly. He told us to put it at 1.3 which is the most efficient (so I guess that's the dialer 1-5 NoBritishGas refers to).

Now the numbers probably make more sense. Correct me if i am wrong though. If 1-5 = 8-24KW, then 1.3 would be approximately 10kw*1.1 = 11kw per hour. Then 2 to 3 hours a day including probably more than 1/2 of the time it's not working fully should be less then 20kw per day. Hope this explains the mystery!

Merry Christmas again !! :j

oellph

It's incredibly low whether you have imperial or metric. I have a friend who also seems to use less than 1 unit per day, with heating on 1hr in the morning and about 5hrs in the evening.

Ourselves, although we're £200 in credit from the summer, we are currently averaging 8-10 per day for about 8 hrs of heat, two showers and cooking. That means we're looking at a bill of about £120 for december! :eek:

I can't see how on metric anyone can get below 2-3 units per day in winter ( for a house ), so maybe your flat is making things easy on the pocket.

macman

If the OP can tolerate a temp of 14.5C in the house and has the rads switched off in this weather, then it's not surprising that their gas bill is miniscule. The 'average' house with CH is heated to about 20C in the living area, that will vary from say 18C to 22C depending on individual preferences. But 14.5C is far too cold for most of us.