# Gas consumption

A recent posting has caused me to think about our gas consumption. We have a 28kw combi boiler. If it runs for an hour it uses approximately one unit of gas, which I think equates to 10kw. Does this sound right? We have our heating on approximately 4 hours a day in winter and with hot water, use about 4 units a day. Another posting had someone with a 30kw boiler in 24 hour use consuming 5kw a day which sounds a lot better than our system.

If it runs for an hour it uses approximately one unit of gas, which I think equates to 10kw.
Depends on whether your meter records cubic metres or hundreds of cubic feet.

I M³ per hour is about 11kWHr but 1 hundred ft³ per hour is about 31kWHr

Another posting had someone with a 30kw boiler in 24 hour use consuming 5kw a day which sounds a lot better than our system.
No. They were consuming 5 units a day, but did not say what the units were.

Our meter is in cubic meters, so it could be the other system to which I refer is cubic feet.

Depends on whether your meter records cubic metres or hundreds of cubic feet.

I M³ per hour is about 11kWHr but 1 hundred ft³ per hour is about 31kWHr

I know it's me being pedantic but a kWh is a quantity of energy and is equivalent to a volume of gas. Really the "per hour" bit is redundant.

Depends on whether your meter records cubic metres or hundreds of cubic feet.

I M³ per hour is about 11kWH but 1 hundred ft³ per hour is about 31kWH
I know it's me being pedantic but a kWh is a quantity of energy and is equivalent to a volume of gas. Really the "per hour" bit is redundant.
Not really, as it's the rate at which gas is consumed which is important. A 30kW boiler will consume gas at twice the rate as a 15kW boiler. A boiler which consumes 1 cubic metre in one hour is an 11kW boiler and it will have used 11kWH of energy; while a boiler which consumes 100 cubic feet in one hour will be a 31kW boiler and will have used 31kWH of energy - assuming in both cases that the boiler is alight continuously for the hour.

In any case, the point I was making is that you need to know what the units are, before you make comparisons based on units consumed.

I take your point but if you look at the sentence I quoted you equated cubic metres per hour and kilowatt hours.

Just done a 7 day meter reading from 5pm 1 December to 5pm 8 December. Boiler is a 42kW combi serving 13 radiators (3 double) in a 1990 smallish 4 bed detached house with one and a half bathrooms. House has been well insulated. House temperature set to 20C. Boiler is set to 65C for the radiators and 60C for hot water.

Radiators are on for 7.5 hours a day Monday to Friday ( 1.5 hours in the morning 6 hours at night) and 15 hours on Saturday and Sunday. Consumption during this cold period was 41m3

Since October 16th until 8th December we have used 194m3 or gas units which is 2170Kw over 54 days, noting that we were away for 9 days at the end of October.

This has cost £84.78 at a consumption of 48kW / 4.3 units per day over 45 days excluding the 9 days we were away.

Grand total per hour is 4.97Kw based on an average 9.64 hours a day radiator usage.

Lets not forget that my 42Kw boiler is only 42Kw when the taps are on full. I have worked it out roughly that the radiators require around 9 or 10kw if I did my sums right.

edited

Thanks for your comments Ltnman. We have a two bed house (with cavity wall insulation) so it sounds like we're not getting best economical use from our boiler.

Does anyone think our costs would go up much if we ran the boiler all evening and more at weekends? ie, is it cheaper to just run the heating when you really need it, or run it all day and not having to heat everything back up?

When the heating is off and the temperature inside has fallen, the heat loss will be lower. Keeping the heating on all day will result in greater heat loss and will inevitably cost ypu more.

I suppose you could experiment a bit to find out how much difference it would make in practice but personally I prefer letting our house cool down (within reason) while there's no-one around to benefit.

it is next to impossible to do a reliable test because there are too many variables.
plus 1c and strong wind will cool off more than minus 2 sunny winter day.
people will adjust the roomstat because they feel too hot or too cold and the override because they are more home than normal or less.
there are 2 things that will safe you money no matter what house, where or what boiler; turn down the roomstat and heat fewer minutes per day.

I take your point but if you look at the sentence I quoted you equated cubic metres per hour and kilowatt hours.
OK. I was being sloppy. What I should have written was: if a boiler consumes 1m3 in one hour, it will have used about 11kWH of heat.

If it runs for an hour it uses approximately one unit of gas, which I think equates to 10kw.
Depends on whether your meter records cubic metres or hundreds of cubic feet.

I M³ per hour is about 11kWHr but 1 hundred ft³ per hour is about 31kWHr

Another posting had someone with a 30kw boiler in 24 hour use consuming 5kw a day which sounds a lot better than our system.
No. They were consuming 5 units a day, but did not say what the units were.

I can confirm that my measurements of units were in hundred ft³ (1 unit = 32.33KWHr)

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