What is the approximate cost of UK gas per cubic foot ?

thesled

Which is useless, because that's not what the meter reads in, which is the whole original point. 
However there is another factor which does need taking into consideration which has a much more major effect.
The electric heat can be considered 100% efficient for the purposes of, whereas the gas/radiator system will depend on other factors and will be considerably less. So although the gas is a quarter the price of the electricity, by the time you've factored in efficiency losses the saving will be considerably less leading it back towards being probably nearer half of the cost than a quarter. 

matt_drummer

thesled said:

Which is useless, because that's not what the meter reads in, which is the whole original point. 
However there is another factor which does need taking into consideration which has a much more major effect.
The electric heat can be considered 100% efficient for the purposes of, whereas the gas/radiator system will depend on other factors and will be considerably less. So although the gas is a quarter the price of the electricity, by the time you've factored in efficiency losses the saving will be considerably less leading it back towards being nearer half of the cost than a quarter. 

It's on your bill.

About 11.2 kWh per m3

Your gas boiler should be about 90% efficient.

That means heat going into your house is about 7p per kWh compared to electricity at 25p per kWh, depending on tariffs.

So maybe 3 to 3.50 times cheaper, gas to electricity.

It's basic primary school arithmetic.

Gas meters cannot measure kWh's, only volume, but the quality of gas varies a little.

Price per kWh for each makes it easy to compare costs, you just need to take into account that gas boilers are not 100% efficient.

It will always be cheaper to heat with gas than electricity unless you get a heat pump installed.

thesled

I'll tell you what, my gas boiler is nowhere near 90% efficient. But the boiler is only part of it - you have to look at the whole system. 
The vagaries of systems efficiency meaning having a direct, accurate comparison between electricity and gas prices (via kWh) is not only pointless but also very misleading. People need good rules of thumb they can actually use, not irrelevant theory. 
Also, real world experience says heat pumps are not always cheaper than gas even if they are in theory - and if you factor in the massive up front cost you've no chance. 

matt_drummer

thesled said:

I'll tell you what, my gas boiler is nowhere near 90% efficient. But the boiler is only part of it - you have to look at the whole system. 
Also, real world experience says heat pumps are not always cheaper than gas even if they are in theory - and if you factor in the massive up front cost you've no chance. 

My heat pump is miles cheaper than gas!

Heat pumps can be installed for less than £1,000 by the likes of Octopus and British Gas, and then there are the ECO4 schemes that are effectively free.

The boiler is the only part of it that matters, how much of the heat generated from burning the gas gets transferred to the water flowing through your radiators. That's it.

A modern condensing gas boiler that is working properly is over 90% efficient.

Ectophile

Bear in mind that the black figures on an imperial gas meter are hundreds of cubic feet.  1 unit = 100 ft³.  The conversion factors on gas bills allow for this.

thesled

FreeBear said:

thesled said: Gas used to be measured in pence per therm. For wholesale gas market purposes it appears it still is, because gas traders don't want to get bogged down in nonsense. A therm is 100 cubic feet, so all pretty easy. However of course the wholesale price is not anybody's retail price.

Nope. A therm is a measure of energy equal to 100,000 BTU or approximately 29.3kWh.

If you are converting a volume of natural gas to kWh, BTU, or Therm, you'll need to know the calorific value which varies from day to day and also a conversion factor to account for variations in pressure.

Diddley squat of importance. The conversion factor is 1.038 or near as dammit unity that it does not matter for the purposes of the exercise. 

QrizB

thesled said:

FreeBear said:

thesled said: Gas used to be measured in pence per therm. For wholesale gas market purposes it appears it still is, because gas traders don't want to get bogged down in nonsense. A therm is 100 cubic feet, so all pretty easy. However of course the wholesale price is not anybody's retail price.

Nope. A therm is a measure of energy equal to 100,000 BTU or approximately 29.3kWh.

If you are converting a volume of natural gas to kWh, BTU, or Therm, you'll need to know the calorific value which varies from day to day and also a conversion factor to account for variations in pressure.

Diddley squat of importance. The conversion factor is 1.038 or near as dammit unity that it does not matter for the purposes of the exercise. 

The difference is due to the supply pressure

 A therm is approximately equivalent to the energy in 100 "standard" cubic feet (of gas at a standard composition) but the gas your meter measures is at a slightly elevated pressure.

The 3.8% difference is roughly one kWh, so 100 metered cubic feet contains just over 30kWh of gas. If you were using 30 as your conversion factor, you're closer than you thought.

thesled

Indeed. So the basic answer, dodging all the noise, is that one unit (measured in the black digits - ignore the red ones) of gas on an imperial gas meter (for 100 ft3 or cubic feet) costs about £2 if you're on the standard capped tariff. 
For our friends who have metric meters (m3 or cubic metres) it would seem to be about 70p (£2/100*35).
Like I originally said, getting a straight answer to this isn't easy and you probably now see why. 

Ildhund

'About £2' probably spans a fairly large variation. The weediest gas your supplier is allowed to sell you has a calorific value of 38 MJ/m³. 100ft³ of this gas would provide about 30.5 kWh, which at the cheapest price per kWh - which varies according to where you live and how you pay -  of 6.10 p + VAT would set you back ~£1.96, so not far off your £2. 

Calculate it again using the strongest gas (41 MJ/m³), you get 33.0 kWh. At the highest price of 6.97 p/kWh + VAT, your approximate cost is 23% higher, at ~£2.41.

Given that the typical household consumes about 36,000 ft³ each year, your approximation could mean £80 either way on an annual bill. Is that good enough?

thesled

Theoretically, theoretically, theoretically, Yes, theoretically. 
In practice the calorific value rarely ranges outside 39-40 and even the industry recommends using a ballpark figure of 40. The chances of consistently providing very strong or very weak gas at the extremes of the range for any length of time is unheard of. 
So in practice this makes next to no difference. It may change slightly over time but is far more likely to be knocked aside by much bigger changes - the most obvious one being the basic price of the gas. 
So in short, pending a significant change, the most likely one being the basic gas price, the figure of £2 is absolutely fine for the purpose, which is to provide a ballpark figure over a short term period.