Excessive gas consumption

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We have a 10 year old Worcester Bosch 35CDI boiler. Possibly, a little undersized as its heating output is 25 and water 10 and we have 18 radiators. Last summer, April - September we used 90 units of gas in total, when using system for hot water only. Over the winter we have been consuming 30 units per day. We moved in 15 months ago. The house is 4 bed detached, around 240 Sq metres and boiler uses one unit of gas or 25 KWH per hour when it is heating whole system. The boiler rarely goes off when heat is being called for and house never overly warm.

Central heating experts have visted but no one can find out why we have such excessive consumption. Heat loss engineer says heat loss cannot explain usage, cavity walls are filled and lofts properly insulated. British Gas have checked metre and it is fine, no leaks, no leaking taps. In winter, the gas bill is around £100 per week for 3 hours heat in the morning and 6 in the evening at 20 degrees. We need Sherlock Holmes but getting depressed as we need to spend so much to heat our house and no one knows why. If you can help, I will be very grateful.
 
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Have yo gas rated the boiler when running the CH at full tilt?

Time the red needle as it completes one full revolution.

Your boiler should be fine for the property.

Are you fully double glazed? What qualifications did this Heat loss engineer have?

Do you have a programmable room thermostat and trv's
 
The house is 4 bed detached, around 240 Sq metres and boiler uses one unit of gas or 25 KWH per hour when it is heating whole system.

Not sure what's going on here - does your gas meter read in cubic metres or cubic feet?
 
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Thank you for your comments and for taking the time to respond. We have two room thermostats for two central heating zones and every radiator but for towel rails has thermostatic control. Just dug up some wooden floor boards ( not because of your question) due to heating engineer, all pipes insulated. Engineer works for local building firm and qualified to do commercial heat loss calculations. Seemed to know what he was doing. House fully double glazed although we do have draughts but engineer said heat loss could not account for all this gas usage.

Not sure what you mean about red needle as we don't seem to have one but heating engineer calculated that we use one unit of gas per the metre for every 27 minutes of the boiler at full tilt. This is approximately 25 kwh per hour. The boiler just never goes off when heating is being called for. It is on constantly.
 
Gas metre is cubic metres and the bill is the metre reading times a factor of about 11 to reach kwh then times the price. This is how I have worked out that one unit of gas per the metre feeds the boiler for 27 minutes and this amounts to 25 kwh per hour. If we have heating in the winter for 3 hours in the morning and 6 at night this is 225 kwh per day plus for cooking and small gas fire and this is around 1500 per week. The weather has been so cold lately I have had heating on all day and I have used much more hence my despair over size of bills.

Have paid three different heating engineers to visit at a cost of over £100 each per visit and each conclude it is heat loss. Heat loss engineer says there is a problem with the central heating as heat loss cannot account for such figures. Not sure who else to turn to.
 
I would argue with British Gas over the state of the meter. they can be reluctant.

If you are only reaching 20 degrees the heat has to be going somewhere. The boiler may not be the most efficient out there but it's not that bad.

Take a meter reading now, run the heating at full tilt for two minutes then read it again and post back.

You may find it easier to run the hot water.

heating output is 25 and water 10 and we have 18 radiators.

This does not make sense can you translate for us?
 
We have a 10 year old Worcester Bosch 35CDI boiler. Possibly, a little undersized as its heating output is 25 and water 10 and we have 18 radiators.
Are your sure it is a 35CDI, not a 25CDi? The 35CDi will give 30kW heating output.

Over the winter we have been consuming 30 units per day.
Are the Units in cubic metres or hundreds of cubic feet?

boiler uses one unit of gas or 25 KWH per hour
The 35CDi is rated at 3.7 cubic metres per hour or 1.31 hundred cubic ft per hour.

3 hours heat in the morning and 6 in the evening at 20 degrees.
Do you let the house go cold during the day or is there a set-back temperature while you are out?

What heating controls do you have, e.g room thermostat, thermostatic rad valves?


My current (winter) consumption (4 bed detached - cavity insulation, DG and about 100mm loft) is 117kWH per day. In the summer it is about 20kWH per day.
 
Dear Dan,

Thank you for your help with this. We thought it must be the metre and British Gas took the old one away to be tested last February. They said the test results were inconclusive and installed a new one. The new one is giving these readings as well.

Since I wrote the first entry I have been recording the metre. Between 15.50 and 16.50 the metre moved 1.743 that is with 2 house thermostats at 20 degrees for both zones and heating and hot water running. A 2 minute reading gives a change of 0.0473 although we have had heating on for most of today as it is so cold. The gas metre is outside the house but it doesn't move when we turn the whole system off.

I agree with you, where is all this heat going Thank you for your help.
 
It is definitely a 35 CDi. One of the heating engineers told me it was split 25 to heating and 10 to water so perhaps they got that wrong.

If it is rated at 3.5 cu metres of gas per hour, does that mean that is what the boiler will consume if being used to capacity i.e. at full capacity, the metre will move by 3.5 units per hour. If that is so, we are using 2 units per hour which is within the parametres.
 
You said earlier that you use 90 units of gas for the summer months april-september.

Later, you said your summer consumption is 20kWh per day.

20kWh is approximately 1.8 units.

April-september is six months, approximately 182 days.

182 days x 1.8 units per day is approximately 327 units for the six months.


Later you say that your winter consumption is 117kWh per day. Assuming 4 pence per kWh, that is £4.68 per day or £32.76 per week.

You also say that you use 30 units per day in the winter. 30 units per day is 325kWh per day.


Something is amiss.
 
Dear Moggett,

I think you may be confusing my replies with one of the other respondees. April - September I used 90 units per the gas metre i.e. the one British Gas read from. I gather this translates to 990 KWH of gas for the 5 month period when we had no heating on but we are not there all the time.

In the winter, I am averaging 25 - 30 metred units of gas as per the BT metre per day. This is around 220-330 kwh per day in the worst part of winter - like now. Obviously it changes a bit according to the weather but it is a lot of gas. I estimate I am paying between £8- £14 per day in the middle of winter for heating, hot water and other gas usage. Heating engineers when visiting confirm the boiler is eating up 1 British Gas metre of gas every 27 minutes or 11 kwh every 27 minutes. Depending on the rate , this is around 40 p for 27 minutes. If you run heating for 9 hours a day in January and sometimes we run it for more, this explains the bills.

Sorry if all these changes from metre to kwh to boiler units are confusing. I find it so myself but unfortunately , the bills are real.
 
Later, you said your summer consumption is 20kWh per day.
You were quoting me for the summer!

mogget also said:
Later you say that your winter consumption is 117kWh per day.
That was me as well!!

leonine98 said:
If it is rated at 3.5 cu metres of gas per hour, does that mean that is what the boiler will consume if being used to capacity i.e. at full capacity, the metre will move by 3.5 units per hour. If that is so, we are using 2 units per hour which is within the parameters.
Yes, if the boiler is alight continuously for an hour it will consume 3.5 cubic metres, i.e 0.117 cu mtrs in two minutes.

When you measured your consumption over two minutes, you say you used up 0.0473 cu mtrs. Was the boiler alight all the time?
 

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