Would leaving boiler on all day increase bill?

Master of None · 1 Mar 2012

plumbplumb said:
Boiler uses 2.7m3 of gas per hour.

Run it for an hour a day. Gas used 2.7m3

Run it for 10 hours a day. Gas used 27m3

Don’t agree,
If you have decent thermostatic temperature control and you have your boiler on for 12hrs a day or 24hrs a day you are still only overcoming the insulation losses of your house.
The only difference being if outside is 5degC and inside is 22degC the delta T is constantly 17degC if the boiler is on 24hrs.
If you run the boiler for 12hrs per day, the delta T will drop from 17degC to maybe 9degC (Temp in house after 12hrs 14degC)if your house is fairly well insulated.
So the difference becomes the heat loss difference between 17degC (on 24hrs) and an average of 13degC (on 12hrs) delta T which I would have thought is very little. And of cource this diference in delta T only occurs for 12hrs anyway usually during the day when its warmest outside (when you are at work)

bell824 · 1 Mar 2012

libby lou lou said:
My dad, in the olden days believed with, our diy fitted oil boiler and rads, said, "if you don't warm the bricks, then the house will never get warm.

YES exactly the theorly my long story relates to, keep the fabric warm cost's you less!!

big-all · 1 Mar 2012

common sense here a boiler running uses gas and electric cycling in and out is not the most efficient
an empty room willl have no other heat input from lights computers electronic gismos or people the room will reduce in temperature gradually with heat loss from say 20 degrees down to perhaps 15 degrees so no gas burned no electric pump running for 10 hours at say 100w[pump and electronics] so you have saved perhaps 10 or 15 kw because the heat loss diminishes with lower temperatures so even if it uses an extra 3kw to boost up to the normal temperature you have saved say 12 kw off gas at say 4p a unit so 50p
plus the 1kw for the electric at say 12p a unit
so thats 62p saved

now the only way you will know the actual amounts saved is by checking actual consumption on 3 consecutive day on each setup with the same outside temperature

now the saving are around £4.50p a week in this example but if your heat loss is twice as much you will loose around 3 times as much gas so around £10 a week or around £100 in the winter months

Dan Robinson · 1 Mar 2012

You assume a constant max load on the boiler though.

bell824 · 1 Mar 2012

Correct dan THEY assume a max demand the theory of 24/7 heating only work on a correctly sized boiler used correctly!!

lets just say my 30 kw combi has been reduced to 10kw heat output for c/h with the rad stat's (trv's) adapted for correct/relevant room temp's required, and rooms not used as often as others doors being closed.

i could garuntee my 24/7 heating cost's being cheaper than a fill fire and **** off boiler install blasting the house of a smaller size being cheaper!

then again my granny won't learn how to suck eggs now as she's to old to teach her new ticks!!!

big-all · 1 Mar 2012

Dan_Robinson said:
You assume a constant max load on the boiler though.

yes i agree otherwise you would have to do several hundred combinations off assumptions to cover every eventuality over the weeks

the colder it is the greater the heat loss the greater the consumption further complicated by other heat sources and heat loss like opening windows and doors the combinations are endless so a few assumptions are nessisery otherwise we wont have a point that we can discuss just endless figures that are meaning less rather than a few ideas that are limited in accuracy but illistrate the point

JohnD · 1 Mar 2012

we can safely know that keeping the house at a constant temperature 24 hours a day, will lead to a greater heat loss than keeping it at that temperature for 12 hours a day.

Heat loss is directly proportional to (temperature difference) x (time)

big-all · 1 Mar 2012

JohnD said:
we can safely know that keeping the house at a constant temperature 24 hours a day, will lead to a greater heat loss than keeping it at that temperature for 12 hours a day.

Heat loss is directly proportional to (temperature difference) x (time)

plus of course the consumption for the pump/valves/other circuits is never considered in this equation so from this point alone the consumption could be perhaps 10% off extra costs up to say 50% so an additional cost in the equasion but never included but could be very important at 12 to 25p per kw unit

ALEC1 · 1 Mar 2012

once you throw in thermal mass of the building, and hours of occupancy rates things may change.

and to match heat loss to heat load, you need compensation controls, you just cant do it with on-off control.

and finally, as has been pointed out, heat loss is a function of dekta t between inside and out, and in the UK this changes a great deal. over a 24 hour period...

there are too many variable factors to say either way, but i do know people who do it and they claim to use no more energy...

what is certain is the use of compensation controls compared to on-off controls does save energy, my clients report that savings as high as 20% are possible. In these cases the heating is on 24/7 but temperature profiled 21c at day and say 18c at night and when the occupants are out...

JohnD · 1 Mar 2012

ALEC1 said:
...and finally, as has been pointed out, heat loss is a function of dekta t between inside and out, and in the UK this changes a great deal. over a 24 hour period......

and however much you complicate the question, there is no way that 24 hours heating can ever be less than partial heating. 24-hours heating will always use more energy.

ALEC1 · 1 Mar 2012

Of course it will, heating load is a function of building usage and temperature difference....

these two vary so the control strategy should reflect both those...

its not as simple as saying off saves you energy (it clearly does) if you want the house to be warm when you get home in the evening...

JohnD · 1 Mar 2012

if you want the house to be warm when you get home, you use the timer or programmable thermostat to turn the heating back on before you expect to get in. It will still always be cheaper than 24-hour heating.

So the answer to the OP

filthyturk said:
Would leaving boiler on all day increase bill?

is "Yes"

mysteryman · 1 Mar 2012

Of course the answer is 'yes', the more the heating is on, the more fuel it will use. However, just because the boiler is switched on does not mean that it is running at full output all the time. It will be modulating and/or cycling on/off. The best form of control is indeed weather compensation. The building fabric does need to be heated properly, this takes time, and needs to be allowed for. Nevertheless, more on times means more fuel use.

The comparison with driving a car faster is not valid. A vehicle's resistance to motion increases greatly with increased speed, at a power of about 2.6. This is what increases fuel consumption at higher speeds.

filthyturk · 1 Mar 2012

Well blimey! Thankyou everyone who participated in this post. Some very interesting points made. It will be interesting for future reference to see how much +/- the bill is. We normally leave both the CH & HW on continuously and use the room stat to switch the CH. However due to the buzzing problem I now switch the boiler off at the isolator spur before I head up the wooden hill. My initial feeling was that as the heating would be on all day the house would be warm and therefore the boiler wouldn't have to graft as much. Once again many thanks

Agile · 1 Mar 2012

John D has clearly explained that supplying the heat loss for longer will use more energy.

I really dont understand how anyone could think otherwise!

But it seems our schools are not teaching physics properly.

Tony

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Would leaving boiler on all day increase bill?

ALEC1

ALEC1

mysteryman

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