How to calculate gas bills in advance
March 3, 2006 11:55 AM   Subscribe

How to calculate the likely cost of my winter Gas heating bill (UK)?

I've just received a huge bill from the Gas supplier (£600 for one quarter!), so I decided to try investigate how much Gas I *should* be using, but I can't find it anywhere.
Yes, the current reading is estimated, but the last reading was from an actual meter-reading. I can't actually climb up high enough to read the meter myself, but from what I can vaguely make out, the reading looks way higher than they've even estimated.

I've searched online for hours and called the Gas board, but can't find any way of calculating a likely least / most scenario of how much I should be paying, or how many units I should be using.

It's a 1 bedroomed flat. Single glazing throughout, high ceilings. 5 radiators in the flat. Three of those are double, and one is permanently switched off, so that's 7 radiators, all of which are small. (not the huge 6foot versions). I have a combi boiler (Baxi - don't know the model.). I leave the temperature in the flat at 20degrees during the day when I'm out and whack it up to about 25-30 when I'm in. Any lower than 20 during the day, and the flat doesn't warm up at all by the time I go to bed. (I have Raynaud's so I need to keep a comfortable temperature). I don't have any other Gas appliances - it's just for central heating and warming up water.

Is 20-30 degrees above average for heating temperature? What temperature do others keep their heating at? Is there any way I can calculate how many units / kwh I would be using in this scenario? I'm looking for something like "The least you're likely to pay is £x and the absolute most you're likely to pay would be £x type of scenario.

(I know that the bill is most likely wrong, and I do have someone coming to read the meter next week. I'm also going to get some step-ladders and read the meter every day for a week to work out my consumption. But I'm still curious how to calculate this.)

Can anyone help me here? I swear, if I find out how to calculate this, I'll set up a website so others can do the same!

posted by lemonpillows to Home & Garden (9 answers total)
Unfortunately, this is the kind of thing that's extremely difficult, if not impossible, to calculate. The variables include:

1) Size of your home.
2) Number of windows/doors in your home.
3) Family activities (how often windows/doors are opened through the heating season).
4) Efficiency of your furnace/boiler.
5) Type of thermostat used (normal or programmable) and setback temperature/time if programmable.
6) Outside temperatures.
7) Cost of electricity or other heating fuel.

The main items that will affect your costs things are numbers 6 and 7.

Heat loss increases when the outside temperature decreases, so your heating system has to work harder when it's colder to maintain the same inside temperature. If you've found a way to reliably predict the weather, you'll have enough money that you won't care how high your heating bill might be.

As to number 7, the cost of electricity/fuel can vary greatly, depending on where you live.

As to your question about indoor temperatures, I have a programmable thermostat, and keep the temperature at about 21C in the morning and evening, 17C overnight (I sleep better when it's cool), and about 16C during the day when the home is empty. I have a forced air furnace, though, so it's easier to raise the temperature after the setback period.

One thing you might look into is whether your gas supplier has an "equal payment plan" where they estimate your usage over the entire year, and charge you the same amount each month, with a "balancing out" of the amounts owing (to you or to the supplier) once per year. It won't help you with the overall cost, but it at least can make the payments more predictable.
posted by gwenzel at 1:01 PM on March 3, 2006

Heating bills (from natural gas, electricity which also need natural gas to run the turbines, and heating oil) are high everywhere. Here in the U.S. skyrocketing bills have been a big concern with newspaper stories appearing every day about how will folks get through the winter.

The energy price situation in the UK appears to be no different than here, apparently.

In short, energy prices have been skyrocketing around the world for various reasons, including more demand from places like China as they modernize.

Maybe there is a meter problem. I don't know. But to some extent it may be a case of "we're all in the same boat."

I feel your pain, as Bill Clinton would say. :)

...and don't get me started on gasoline prices!
posted by bim at 2:07 PM on March 3, 2006

Here's a very clear article on the situation from the BBC.
posted by bim at 2:16 PM on March 3, 2006

£600 for a quarter?! I can't help with the calculations, but have you checked out uswitch and Which? magazine's Switch site - they might be able to get you a cheaper supplier.
posted by TheDonF at 3:24 PM on March 3, 2006

Heat loss goes up by the square of the temperature differential, so it doesn't just go up, it goes up a lot!

0degC outside, 20degC inside, power loss = Kx400
0degC outside, 30degC inside, power loss = Kx900
(where K is an unknown constant)

So that 10deg difference causes more than double the heat loss.

Don't most people start sweating by about 28deg? Room temperatures above 26 are pretty hot, I wonder if you have an accurate enough thermostat to judge what the real temperatures are... Get a thermometer and check it out.

I guess you don't have a history for this flat, because if you did, that would be the first place to start.
posted by Chuckles at 6:21 PM on March 3, 2006

Dear lemonpillows,

I won't tell you how to calculate you annual heat bill (its complicated - so actually hard just complicated and the answer depends on so many factors that its not that worthwhile apart from being a ballpark.)

However some hints to cut your bill -

1) Get double glazing. Its likely that the air infiltration from your old windows makes your flat cold. They normally pay for themselves in 2-3 years, esp. in a high ceiling flat.

2) Do not use electric heaters. They are expensive and very poor value.

3) Turn off your heating during the day. You are pouring money down the drain. Whack it up to 30 when you come in. This will asave you a lot of money.

4) Has the boiler been serviced? It may be wasting gas.

5) Get a step ladder and record your consumption on weekly basis then take measures to manage your supply

If you are sincere about the website i can help with the technical actual calculation stuff (its my job). Email me direct if you want any further advice. I caveat this by saying i do very little domestic heating installation design. I am a large scale services engineer (see and
posted by Vroom_Vroom_Vroom at 1:47 AM on March 4, 2006

That bill is ridiculous. It's definitely wrong. Are you sure you're not paying for a previous tenant's/owner's amount too? Gas companies do get meter readings and estimates wrong, so really dig into this!

We have a two bedroom house that's mid-terrace. We pay for gas on a stupid card at the shop (god knows why, beacuse our electricity and water are done the normal way) which is overpriced. We spend about £40 a month on gas, which I think is a lot for what we have.

I'm in the house nearly 24 hours a day, but keep alternating between 15 (which, in our house, effectively means the boiler is off) and 20 (which effectively means the boiler is on). We only have single glazing, but it seems to stay warm.

In my research of other people's spending, £30 - £80 a month on gas is the range about 95% of homes fall into.
posted by wackybrit at 3:37 AM on March 4, 2006

We have a 4br mid-terrace (loft-converted). One side has been empty this winter due to construction, and the party wall has been very cold.

Knowing that gas would be expensive this year, we've tried for 12C when we're not here, 17 when we are and about 15 overnight.

Our bill from February was about £200 for the preceding quarter.

On that basis, I would say that £600 for a 1br is way too much, even with the heat turned up in a draughty flat.

Some local councils have money available for energy efficiency projects (ours hasn't offered).

I ran some numbers on gas vs electric and oil. Gas from London Energy was averaging me £0.02/kwh. Oil is about £0.035, and electric is about £0.033 on Economy 7, about £0.08 on regular tariff and £0.10 on Economy 7 during the day. So I concur with previous poster that gas is your best option, but check your kWh price.

The gas prices above applied before the recently announced cost increases by some of the gas companies. The increase announced was headline 22%. Gas is still the cheapest option, but it's moving closer to oil parity, which is probably the reality for the UK future.

One area you ought to check. When you get your bill and there has been a tariff adjustment, make sure that either the estimated or actual reading benefits you the most. Check your meter versus the estimate and determine if it makes sense to phone in an actual reading to take advantage of the lower tariff. If your meter is way over the reported reading, it might make sense to phone in the accurate reading to make sure that those units are charged at the lower tariff.

Look on the back of your bill and it explains how to calculate the total charge. Remember that units on the meter do not equate to kWh on the bill - there is a conversion factor applied.

I agree those who say to make sure you check your meter regularly and make sure something isn't amiss. And see if you can get history. They used to do this but don't seem to any more. I checked our bill last year and we've used 9600 kWh this year vs 12100 last year in the same period.

Hurry, Springtime!
posted by sagwalla at 9:14 AM on March 4, 2006

Thanks for the replies guys.

Unfortunately, a lot of the 'energy saving' measures are beyond my control as I rent the flat.

I think the best option is to make sure I'm in a warmer flat for next winter! (And make sure I keep an eye on the meter).

It does look a little complicated to work out. Especially having to factor in the temperature outside versus how much heat you're losing. Bit beyond the simple service I was hoping to build. Never mind!
posted by lemonpillows at 2:08 AM on March 6, 2006

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