We have all experienced the phenomenal rise in the costs of domestic electricity and gas in the last few months and this has focused us on the need to better control its use. After scanning the Internet for practical advice, it came up with all of the usual advice that you would expect, use energy saving bulbs, switch off chargers, turn your thermostat down by one degree etc. etc. Although this guidance is very useful, I could not find much discussion about how much gas typical houses used throughout the year. Even in chat room discussions, I could not find too many places where the actual amount of gas used was discussed. Moreover, we all know that we use more gas in the winter than the summer but I wanted to know by how much and what were the main drivers behind the horrendous quarterly bills I had been receiving in 2008.

You can download an annual average annual gas consumption graph in the UK. An approximate guide to gas consumption according to house size from the now defunct EnergyWatch site is shown below:

I felt that I needed to gain more understanding and that if I achieved this then I would feel to be in more control. I'm happy to say that I believe that this has been achieved and my analysis of electricity and gas usage has really helped me to reduce my energy bills by more sensible use of gas central heating and electrical appliances. I hope you find it useful. Let me know if you do: Email:

Top of my list was to understand how gas use changes during the year which is clearly dependent on outside temperature, especially so during the winter. So, task number one was measure gas consumption on a daily basis. This is quite easily achieved by reading the gas meter at the same time each day. Shown on the left is a typical gas meter and if the gas used each day is to be accurate, it needs to be read to at least decimal places e.g. 10884.33. This is not at all onerous and takes only a couple of minutes.

If your gas meter is outside of the house, you might need to get hold of a gas meter box key like the one shown on the right. I'm not sure where these are available from but I'm sure they shouldn't be too difficult to get hold of.

I also started measuring the outside temperature each morning as well but I soon came to the conclusion that the outside temperature was lower at some time in the middle of the night.

As I assumed this was a key factor in how much gas it took to heat my house, I invested in a low-cost maximum-minimum electronic thermometer available from Maplin. The one I purchased will measure inside temperature and had an external temperature sensor on the end of a 2-metre lead which can be placed through a convenient window. I was now able to measure both the minimum night temperature and the daily gas consumption so I was ready to go!

The next task is convert the daily gas units used to Kilowatt Hours (kWh) as this is what your gas supplier uses to create your bill. You will need to get the exact formula from your own gas supplier. The one shown below is British Gas (Incidentally, the calorific value has changed in the last few months from 38.8386, a change that favours British Gas from a billing uplift of 1.009% [Dec 2008]):

Converting units to Kilowatt Hours
( Your local calorific value )

Of course, this is not calculated manually each time but is achieved using an Excel spreadsheet as shown below. It's quite easy to convert the calculated kWh/day to monthly and quarterly estimates and multiply by the pence/kWh charges supplied by your gas supplier on your quarterly bills.

Gas consumption analysis spreadsheet

I found the results of the monitoring very interesting as can be seen in the graph below. Before looking at the graph you should know that:

• Our house is quite a large old 1932 four bedroom detached house.

• We also use gas for cooking and.

• The central heating boiler is an old Potterton Netaheat ( Boiler efficiency database ) and is not as efficient as a new condensing boiler.

The graph covers three periods of gas usage. The first period gas is used for cooking and heating the hot water tank (more on this later). For the second period, the gas central heating is only turned on for a single period in the morning. For the third period, the gas central heating is turned on twice a day - morning and evening. The two peaks show when I had the gas on all day - not something I plan to do every day.

Note 2008: Towards the end September we turned the gas on once per day in the morning . At the beginning of November we had it on twice a day in the morning and evening. During March, the day time temperature has been so high we had the central heating on during the evening only essentially returning to a once a day regime. In the middle of April we have turned the gas central heating off completely and only using it for hot water and cooking. When it has been chilly in the evenings we use our wood fire.

Note 2010: During October, November and December 2009 we have been lighting fires using logs. As the temperatures have been so high this has meant that we have not turned the central heating on in the evenings thus saving a total of over 2000kWatt/hr - a complete month's average usage! We intend to use up this 'heating bank' during the next cold snaps in January and February 2010.

It's got very cold during January 2010 so inevitably we have had the gas on longer, however, we have used less gas due to the use of open fires using free logs!

The 2009/2010 graph shows the outside minimum temperature in red and the amount of daily gas used in kWh in blue. The light red and light blue are for the 2008/2009 season.

Daily Gas consumption (updated 17/8/2010)

Actual gas usage 2008-2009 and 2009-2010 seasons
Updated 18/8/2010

This information enables the precise repay period if the boiler was upgraded to a more modern condensing boiler. In my case it turns out to be five years. I do not think this is worthwhile as my boiler though old is very reliable so I will not upgrade until it finally gives up the ghost!

The increase of gas usage is an additional 6 kWh / day / degree drop in minimum night temperature.

What I learnt from this graph is:

• There is a very direct relationship between the outside night minimum temperature and the amount of gas consumed.

• Having the central heating on for longer times uses more gas (I know it's obvious but the graph tells us the relationship!). This fact makes the prediction of forward gas bills impossible!

• Usage variability is caused by:
   

  • Variations in daily cooking using the gas cooker (though this is irrelevant in winter months!)

  • The manual switching on of central heating for extra hours on very cold days

  • The manual switching off on warm days (> 10 degrees centigrade)
     

• Big peaks show when I had the gas on all day - not something I plan to do every day unless I wish to get mega size bills.
   

• I use coal fires rather than turning the gas central heating on during the day to reduce usage.

It's interesting to compare the variable consumption of gas to the entirely predictable consumption of electricity. The peak during August was before I started looking at electricity consumption and getting it under better control. Once I had achieved this, usage is totally predictable and is around half of what I previously consumed.

I hope that this helps and if you undertake a similar exercise please let me know your results and I'd be happy to publish them here. Email:

Useful links:

• Real-time Web Based Power Charting

• Combi boiler gas consumption

• Average gas consumption

• How to dramatically cut your electricity use 

• what is average gas consumption based

Back to home