Unexpected amount of gas usage

Salfman

Hello
I was wondering if anyone can help me out. My gas meter is reading higher that the estimated usage although I have barely been using gas and expected it to be lower than estimated. I have been tracking the usage and as I have no idea how to calculate anything I'll write it all out. I have a combi boiler for ch and hot water and have had the ch off for the last few weeks. With the hw turned off I got 0.260 cubic meters for less than 3 hours use of one gas ring and 0.011 from less than 5 mins.Then I turned on the hw and checked overnight (no water running by night!) The boiler seems to be using 0.005 cubic meters over 10 hours of doing nothing! Does this make sense? Should we keep it off except for showers? (Cant do that in the winter).
Thank You

molerat

Does the boiler "do nothing" though ? Many have a small reserve tank inside to give you instant hot water and that is kept hot thus using a small amount of gas. In that case turning the boiler completely off would not save much because as soon as you turn it back on it will need to make up that loss. Some also have a pump anti seize which will turn the system on for a short while x hours after the pump last ran.

macman

What is the make and model of your combi boiler, and it's age?
To put this in context, in that 10 hours you used just over 0.5kWh, or about 2.5p: around £9 a year, and about a sixth of the cost of your daily standing charge.
If this is an old boiler, it's probably the pilot light.

Salfman

Thank You for your responses.
It is brand new Baxi boiler (don't remember the exact name) so im not sure why it should be using anything. i spoke to my gas company and they told me their estimate was based on zero usage for some reason so there is probably nothing wrong in the end.

tahrey

My old hot air ducted heating system spaffed away about a full fifth, if not a quarter of all the gas it used just keeping the pilot light burning; I would have shut it off completely at the main tap (and electrical switch for the controls) if only the re-lighting spark plug system wasn't so hopeless that you typically needed to wodge a bit of barbecue firelighter on the end of a bit of stiff wire, ignite it and worm it up into the space where the pilot and plug were to actually restart the system if a stiff gust of wind managed to backwash the flue and blow it out... Once you've done that a couple times your idea of an acceptable idle energy usage alters a bit.

Anyway, my own newer combi boiler (Worcester-Bosch Greenline) has a habit of turning on and running unneccessarily for a few minutes every few hours (never got round to timing it, but I noticed it quite often), no matter what I do with the settings on the "Wave" Smart thermostat or the boiler's own LCD panel, including not only disabling the hot water preheat but turning the demand hot water off entirely (AND reducing the tap and radiator temperature way down).

The pilot doesn't seem to be anywhere near as big as the old system's, so it doesn't use gas as fast when lit, and it's not lit anywhere near as much - the ignition system is, at least for now, utterly reliable - so I wasn't really bothered about the additional cost of it idling like that... it WAS however rather annoying hearing it fire up now and then even with the stat turned to 5'C on a roasting hot day and no taps running! Plus this place is like a sauna in summertime thanks to being on the third floor with huge south-facing windows that are difficult to effectively shutter off, so every extra bit of heat that might be produced inside was a problem.

So, I've made use of the one thing that actually seems to have any kind of effect - the cheap, naff, mechanical master timer switch fitted to the boiler alongside everything else, which I didn't actually want and seems to not be a mandatory item, but the fitters must have left in place as it's a standard packed-in accessory and it was easier than removing it and putting a blanking plate over the gap. Kind of grateful for that bit of laziness now. I don't actually bother with the timer program at the moment (though I might do as backup to force it to turn completely off during working days in winter, now I know it's an option - there's no fear of burst pipes here thanks to rising heat from below, the coldest I ever registered, returning after an icy new year's weekend away when the old heater was broken down, was still about 10 celcius)... instead I just use the on-auto-off switch, flicking it to OFF and leaving it here.

Bingo, boiler stays off and doesn't preheat... though it DOES still turn on if the hot water tap is left open for more than a few seconds. Which is fine by me, really, the shower is electric anyway and it's easy enough to just use the cold taps if hot isn't needed. The additional delay is on the order of 2 or 3 seconds, which isn't an issue in the kitchen, and is minimal compared to how long it takes to flush out all the cold stuff in the pipes between there and the bath or the bathroom sink.

So far it looks like my gas use compared to last year has gone down a small but noticeable amount, vs what was already a steep decline (the boiler was fitted just over 2 years ago), so I can commend this tactic to the house. It's not really going to save you a massive amount, but it does have SOME effect, and if the pilot light etc bothers you, it certainly gets rid of it.

.......aaaanyhow, let's run numbers seeing as I've got my bill next to me.

Total use over one year from May 16 to May 17, 604 cubic metres. That's 50.33 per month, 1.654 per day, and indeed 0.069 per hour.

Conversion factor listed on the bill, to go from m^3 to kwh, is 1.02263 x 39.4, then divided by 3.6, because these people are crazy and won't do something simple when a complicated method can be found. However, the important point is that the result comes to 11.192 kwh for every cubic metre.

This is important to keep in mind, because despite the meters reading in m^3 (essentially, 1000-litre blocks, same as domestic water meters), the bills are calculated in kwh (with the conversion varying due to exact chemical composition of the gas, ground temperatures around the storage tanks and pipes, etc), and so if you forget to do the conversion, or do it the wrong way, etc, you could end up thinking you're using more than 10x or even 100x less (or more!) than you actually are.
((the variability doesn't seem to be much, though - the 1.02263 shown above is actually an average of the two different factors given on my summer 2016 and summer 2017 bills... which were 1.02264 and 1.02262... the other two factors were identical for both years. That's a change of about 0.02%, or 20 parts in a million - in other words if you had a £500 bill for the gas alone, this would cause a change of about 1p overall!))

My figure comes out as 6760kwh for the year, or £264.11 at the ludicrous 3.907p per kwh that E.On was charging me after a stressful work situation led to me letting my tariff slip back to Standard Variable (soon to fall to closer to £169, albeit with a slightly higher standard charge on top, once I get switched over). That's approx 18.5 kwh per day, or an average equivalent to 771 watts continuous across the entire year (72.2p/day, 3p per hour, on the expensive tariff, about 46p and 2p on the cheaper). Which sounds like quite a bit, but E.On's energy tracker says I'm about 10% more efficient than most other already-"green" homes of the same size and type...
((this also means 1 cubic metre is worth either 28 or 44p depending on the tariff))

Hopefully this gives you some context for your own actual usage?

Your gas ring comes to:
0.260 for 3 hours (what were you cooking, and how vigorously?) and 0.011 for 5 minutes... if you were billed the same as me, that's 2.91kwh and 0.12kwh respectively.

2.91kwh into 3 = the equivalent of 970 watts of heat continuous, averaged over that time. 0.12kwh, into 1/12th of an hour = 1440 watts (1.44kw).

Comparing with my electric hobs - on a heat output basis, at least, if we assume that converting electrical input into heat is nearly 100% efficient - that seems fairly normal. About what a medium-small and medium-large ring consume (and thus emit) respectively. Though you get the dual benefits of it costing far less for the same heat (on the example E.On tariff, I pay almost exactly 4x as much for each electrical kwh as each gas one), and being able to make use of more of it because gas burners are somewhat more directional than electric rings... most of the heat goes upwards and against the bottom or around the sides of a pan placed on top, instead of radiating in all directions and having to be reflected back up as best as can be managed.

(I imagine that it's actually the same ring, used in two different ways, though? The latter case for quick-frying something, or reheating some sauce etc, so used briefly at maximum power, and the former for preparing something that takes rather longer to cook, and needs a fair initial burn to get up to temperature, but then sits simmering away for a much longer time at a low setting?)

Compare that even a weedy electric oven is about that same 1kw-ish as the smaller hob, and has to run at that power for a good half hour to get up to cooking temperature (a stronger one is quicker, but uses more energy per second) before cycling on and off with the thermostat, and a typical integrated grill element is closer to the 1.5kw-ish of the larger hob. A microwave is sort of in-between the two, a 2-slice toaster or a George Foreman contact grill / toasted sandwich maker is a little less than the smaller hob, and a kettle comes in somewhere in the 2000 to 3000 watt (2-3kw) range depending on make, size, etc.

(Steamers, rice cookers and slow cookers are special cases, as they tend to have low-wattage heating elements but run for quite a long time; the first two often require you to provide them with preheated water from a kettle anyway, which is cheating, and the latter is very heavily insulated so it can still bring the contents up to cooking temperature, just over a longer period. At the other end, some high powered hobs, ovens, combination cookers can use so much power - especially if everything's turned on all at once - they would overload a 13A plug and have to be hardwired to the fuse box. And if you consider immersion heaters and electric showers as using special kinds of kettle elements, they'd sit at the top end, starting at a "modest" 3kw for a slowish immersion heater and going right up to about 11kw for a deluxe shower, with a crossover around 7.5 between fast heaters and very basic showers.)

So actually your rings are perfectly normal, sitting somewhere in the middle of the expected range of cooking implement energy use. I wouldn't fret about them... the boiler itself will use far more than that when being actively used for central heating and hot water supply, and acts as a demonstration of why all-electric heating and water is so ruinously expensive unless you have Economy 7 or 10, and why it's a really bad idea to fill a bath using an electric shower unless you're desperate. Like 8 thru 12kw if you have a mixer valve shower running off it in the cooler months, and potentially 15, 20, even 30kw-plus (depending on model) for bringing the radiators up to temperature from a cold start in winter. The meter would fair fly round in the latter case, as you'd burn through a whole cube metre in less than 20 minutes (worth about 30-40p remember, so that's maybe 1.5-2.0p per minute, £0.90 to £1.20 per hour, actually not massive).

You'd certainly feel the benefit of that burn, however, as the house would warm up quite rapidly from being very chilly, and after that the boiler would run at a rather lower setting to maintain just enough heat in the radiators to keep a steady temperature. Or at least, that's what it's meant to do with modern electronic, temperature-tracking, weather compensating, multi-level output controllers; a more traditional on-off thermostat will be rather less subtle and simply bang between full power and being completely off (with the boiler controller itself maybe smoothing between the two if it detects a regular pattern), but will all the same still use less gas on average because it spends at least some of the time turned off.

The pilot light use even of my hot air system wasn't so much compared to that - it only seemed to use a lot over the entire year because it became the majority, or only thing using any gas at all (the hot water previously being an immersion heater) during the warmer months, and that was reflected in the average. I can't remember what my actual usage was, but it was into five figures of kwh, so let's make life easy and say 10,000 (a whole-year average of 1141 watts; amazingly, still significantly cheaper when gradually making the flat toasty vs using a single small electric fan heater to keep a single room sort-of-warm plus a low-output portable electric radiator and electric blanket to enable bedroom survival when the gas heater broke down, to the point where it caused an identifiable blip on my bill and caused a direct debit recalculation).

One-fifth to one-quarter of 10,000 is 2,000 to 2,500kwh total for the year, or £50.00 to £62.50 on the cheaper tariff such as the long term fix I had at the time (which is why I would have preferred to turn it off over summer and save £25-30, but was OK with losing that much in return for not having to either make yet ANOTHER service call-out, or use the poke-a-firey-blob-into-the-workings method any more often than I strictly had to). It also works out to a rather surprising 228 to 285 watts equivalent. Not much in terms of heating, I suppose, but enough to make the place a little warmer in summer (especially with the duct fan turned on for some kind of token ventilation), and equivalent in terms of cost to leaving a 60 or 70 watt lightbulb permanently turned on.

Therefore, pretty glad that modern ones are smaller and inherently less costly, and themselves aren't turned on for any longer than they actually need to; essentially they seem to exist to burn up any lingering gas from the main burner after its supply is shut off, and make re-lighting a little easier if there's renewed demand within 5 minutes or so of the last use. It's a small saving in the grand scheme of things, but still one that makes a worthwhile contribution towards a bigger overall change when combined with several other savings of similar magnitude.

Your own pilot light, at 0.005 cube metres (5 litres, or two and a half standard "large" pop bottles) over 10 hours seems pretty minimal. Like, four hours to use up the equivalent of a bottle of pop, at not very high pressure (piped gas isn't compressed anywhere near as much as what's used in a camping stove or cigarette lighter; that 2 litres probably represents less actual fuel than a standard half-litre camping gas canister). It's barely whispering through the meter at that rate, a single cubic centimetre every 7 seconds; some offline back-of-the-envelope maths suggests that to about half what a 50cc moped engine might use at a pretty lazy idle.

Converting it, that's 0.056kwh over the entire time, or a mere 56 watt-hours... and, self-evidently, 5.6 watts average (so in fact that moped would have to have *all* its lights turned off, and have an already fully charged battery, because 11w isn't much in terms of keeping the mechanical bits spinning and the sparkplug sparking a good 20 or 30 times a second, and even LED sidelights and instrument lighting would add enough load to the alternator to stall it). In terms of producing heat from gas it's practically nothing, in fact barely any more than what a USB cupwarmer provides. If it was a continual flame you'd very nearly have to put your finger right in it to get burned. The electric handlebar heaters on my own bike use more than that on the lowest of their five settings, which I rarely bother with unless on a long trip in borderline temperatures because it makes so little difference to how warm my hands are (vs the highest one of 35w, which can get uncomfortably hot in autumn, despite only reaching "tolerably cool" on very wintery days).

I expect it's more likely to be fairly discontinuous, maybe producing/consuming 25 to 50 watts whilst lit - still not much, but enough to avoid being overwhelmed and blown out should a rush of fresh, cold gas come in through the main burner and not catch for a second or two for some reason. Thus cycling on and off, and only being lit for 1/5th or even 1/10th of the time overall. That 56wh use overnight is a mere fifth of a penny all up, or about 1p for two days, 16p for a month, and less than two quid a year.

tahrey

Or, to cut a very long story full of on-the-fly calculations and comparisons somewhat short and much more to the point:

Nothing to worry about, mate. That's all entirely fine from my perspective, and in fact operating quite nicely, so long as the figures you've supplied are accurate and Actual Cubic Metres read directly from your meter.

The hobs come out equivalent to the usage (in pure energy terms) of a 970 and 1440 watt electric ring respectively, which is the typical output you'd expect from medium-small and medium-large examples. Difference is, they're only costing you approximately what a pair of very small and useless 240 and 360 watt hobs would, if your cooker was all-electric, ie saving you about three quarters of that cost

That pilot light is actually very efficient; it's literally using about one-fiftieth as much gas as the pilot in my "recently" replaced 1980s ducted air heating system did. I'm not sure what the pilot in my own boiler uses, as I've managed to manually disable absolutely everything except non-preheated demand hot water for the summer, but I'm now kind tempted to flick it back to full auto and measure how much it consumes over a similar period with no use of the hot taps. If it's about the same as yours, then I might even leave it turned on in case it actually needs to run a little from time to time for the proper operation of the boiler, as mentioned by Molerat, because the additional maintenance cost of any premature wear will distinctly outweigh the minimal saving on gas.

In numerical terms its total use over those 10 hours was barely 1/18th of a kwh, and if you left it like that for 24h without the main burner running at any point, it would use about 2/15th (or 1/7.5th) kwh. Entire consumption for a year without any actual burner use (when that's on, you may as well discount the pilot light, as it's either out, or turned on but actively contributing to the useful heat output) comes to a mere 49kwh, or somewhere between £1.20 and £1.95 depending on (non-prepay) tariff. In reality it's probably responsible for less than 30kwh over the whole year (or 75p to £1.17), which is basically nothing.

In fact, the equivalent average energy use over your 10-hour measurement period is barely more than that of a mid-level ("1.0 amp") USB phone charger, and half that of a typical tablet or fast charger ("2.1 amp") - and the actual cost to you is closer to one-quarter and one-eighth of them respectively. So if you're not bothered about using a tablet charger or fast phone charger for upto 3 hours per day (or indeed 2 hours), the pilot light shouldn't cause you any nightmares, as it'll cost about as much to run as that (or for a final comparison - about as much as a kiddies' LED nightlight left turned on continuously).

All good and clear?

PS - for what it's worth, all the above figures are *exclusive* of VAT, as I'm going by what's on my bill, and of course don't include standing charges etc. However, the latter isn't affected by how much gas or electric you use, and the former is only 5% for energy instead of 20%, so any inaccuracy caused by this will be pretty small and not significantly influence the much larger main message

retepetsir

Talk about TMI from above....

Your Baxi probably has the 'preheat' mode enabled, as mentioned by another poster. It usually is by standard. It usually saves you water, but in doing so does use more gas. Decide whether you want to save one or the other and leave it on or switch it off

r2015

I have a Worcester Bosch combi boiler and it uses no gas when the heating is "off" by being set to 15 deg C on the room thermostat and when not using hot water as shown by my smart meter readings when I went on holiday for 10 days.


During these days the only gas that was used was by my grandson who stayed one night and had a shower before going home.


I knew this because I have the BG app on my tablet and one day while idling some time away in a hotel in Poland, which had free wifi I decided to check how much electricity my fridge and freezer were using, 3 kWh a day as it happens and noticed on Saturday some gas had been used.


The exact amount that having a 10 minute shower used.


My grandson thinks I have the house bugged.


Aren't smart meters wonderful.