Central Heating - On/Off or Always on?

[parapaul]

Been having this debate at work and wondered if anyone here can anyone shed any light on this?

Is it more cost effective to leave the CH on permanently, just using the thermostat to switch the system on/off as required, or to have it on a timer for, say, 4 hours in the morning and again at night?

Common sense says there may be very little in it - the extra energy needed to heat the house from cold may negate the cost of continual smaller 'top-ups', but has anyone ever tested the theory?

And in my house, which doesn't have a room stat thanks to the cheap previous owners, just TRVs on the radiators which I've had fitted - which do we think would be cheaper?

[ymwoods]

According to the British Gas online websaver advice that I have been reading recently it is cheaper to turn it off at night/bed time when not in use and your warm in bed then have it heat from colder in the morning than to keep it 'topping up' during the night.

As such if your going to be out or in bed for more than 4 or so hours I would take a guess as its cheaper to turn it off and either have it timed to turn on just before you arrive/wake or turn it on when you get back.

I am guessing however that a lot of the above would depend on how efficent your system is though at both heating the water to pump to the radiators and also then how efficent the system is at dispersing the heat quickly enough to make any difference or heat your home in any kind of decent time.

[Trikster]

When I moved into my newly build house 3 years ago (ie reasonably well insulated/modern boiler etc) I was advised it was best to leave both the heating and the hot water on all the time as it's supposedly more efficient...

And from a point of view when popping to the loo in the middle of the night - nice for the house to be warm

[TimJMS]

I like the French Windows wide open at night even in winter, therefore it's boiler off here early evening. Ideally I'd have them rigged to an auto closing system when the boiler kicks back in at 4am instead of having two 3kw fan heaters linked to a remote that I flick on to fast thaw the bedroom!

[TooLateForAName]

I think it depends on the building. How much insulation and what sort of thermal mass.

I'm just going over to programmable thermostats. We have an old house where the walls are not thick enough to hold much heat so it gets cold quickly and of course poor insulation (solid walls - no possibility of cavity insulation and conservation area so no external insulation possible). All this talk of warming the house up and letting it stabilise is rubbish for us - the building leaks heat faster then we can sensibly put it in - just as well that we like a cooler environment (thermostats never set higher than 16C)

To know for certain you would need to model it and see how the house looses heat and how efficiently your heating system delivers heat.

[HiRich]

The simplest answer is that there are so many factors unique to you, such as:

• How heat efficient (insulation and draughtproofing) your house is
• How efficient your boiler is in start-up and tickover modes
• How much time you are actually in the house/ really need heating
• How fixed are your patterns - do you get home from work at 6.00pm every night or can it vary from 5-9.00?
• How you use the house (do you need the heating fully on in every room, do you keep doors closed, are there other heat sources such as the oven in the rooms you use most?)
• Do you get any benefits from solar heating?
• How cold is the weather?
• What are you actually prepared to put up with (at certain times of the day can you live with 15 degrees rather than the full 21? Do you need to come in to a piping hot house at night, or can you live with a 45 minute warm-up period?)

that every case will be different and you will only know by trying.

I think it's fair to say that for each house, there is a threshold where your usage/preferences would make it viable to keep the heating on permanently. Permanently on, and no adjustment of the thermostat means you are unlikely to reach that threshold, unless you are in the house nearly 24/7. If you adjust the thermostat as necessary and frequently, it brings that threshold down. If you use a time/temp thermostat (different temperatures at different times), and you have on-radiator thermostats (either time controlled, or that you wind down in regularly unused rooms like the spare bedroom), it will bring it down again.

As an example, I only have the heating on for a short while in the evening. I'm regularly out, on a random pattern, I mainly live in the kitchen/living room, so the oven or iron often supplant the central heating. And I'll put up with a bit of cold (I'm out so quickly in the morning I don't notice it, and I don't have a wife to moan). So for me, I'm way off that threshold. Money is better spent on insulation. But if I do a serious job on the central heating system, I would fit the all-singing time-controlled thermostats everywhere.

Your circumstances will be different.

[stefd]

Typically boilers are far more efficient at full-load than part-load. This is the crux of it really because ultimately heat-in has to equal heat-out. Unless, of course, you let your house drop to ambient temperature (meaning no more heat-out) but this is bad news for the building fabric this time of year.

[Deva Link]

TooLateForAName said:

I think it depends on the building. How much insulation and what sort of thermal mass.

I'm just going over to programmable thermostats. We have an old house where the walls are not thick enough to hold much heat so it gets cold quickly and of course poor insulation (solid walls - no possibility of cavity insulation and conservation area so no external insulation possible). All this talk of warming the house up and letting it stabilise is rubbish for us - the building leaks heat faster then we can sensibly put it in - just as well that we like a cooler environment (thermostats never set higher than 16C)

I think all the above is correct for many properties - we have a largish, but poorly built, 60's detached house and in the kind of temps we've got now (freezing) the boiler is running pretty well continuously. Have the stat set at 23C though! So in terms of gas usage, it obviously makes sense to turn it off whenever possible.

I don't think 16C is a normal temp in centrally heated house and for most people running CH in the low 20's it would surely be too warm at night. Therefore a programmable stat would be very useful.

Interestingly my elderly Godmother had some council people round who keep an eye on old people and they'd been told on a course recently that's it's more cost effective to leave CH on all the time. I've seen various studies on this over the years and that's never been true.

[Simpo Two]

My heating system brings the house up to decent temperature in about 30 minutes in the morning - which is better (and probably cheaper) then having it firing up at random intervals through the night and waking me up.

Whilst the accuracy of thermostats is I think questionable (you may set it to '16' and like it but is it really 16?) I personally like to start the day at an indicated 16 and gradually increase it to 19-20 during the day.

[Deva Link]

Simpo Two said:

My heating system brings the house up to decent temperature in about 30 minutes in the morning -

.....

I personally like to start the day at an indicated 16

Each to their own and all that, but 16C (61F) isn't what many people would call a "decent" temp!

I'm not surprised your CH can achieve that in 30mins - it's not actually having to do anything! Even in our very leaky house the temp only goes down to about that level at night with the CH off unless it's exceptionally cold outside.

[Ferg]

A lot depends on what sort of boiler you have. Modern boilers aren't actually condensing a lot of the time if they are on-off-on-off. However, factor in 'modulating' gas valves and the whole thing becomes far more complicated.

I'd say that on-off-on-off was much better if you have decent insulation and if you HAVEN'T, then get some.