[Closed] Heating - during the day (or night) off or on low?

Discuss? This has to be one of the most frequent questions on DIY and household fora. The problem is that it's impossible to make a 1 week on vs. 1 week timed comparison because of weather variations.

The point to remember is that in order to feel comfortable your internal walls and fittings need to be warm. It takes time for tons of block and timber, plasterboard, furniture etc to warm up to the ambient temperature so in my book you're better running the CH constantly on 18 or 19, rather than flogging the boiler twice a day. This is especially true if your loft insulation is good. If it's only the minimum 100 - 150mm, there's never been a better time to buy glass wool and add some more layers; we halved our gas bills in two houses we've owned when we doubled up the insulation. I'd be willing to bet that with a good layer of insulation it's cheaper to set your CH to on "permanent" and just drop the room 'stat to 18 while you're out or in bed.

Insulate the home properly and it won't even be an issue.

I have ours set to 15 during the day and night and 20 when we are in...

I think I have only heard it click on once in the night.

My Mum has hers on permanently set to [i]Tropics[/i], I literally start passing out when I'm round there 😆

I only have our heating on when we feel the need for it (i.e over ride thermostat) as some days we might be in late- why continually heat a house if no ones there?

hmm ok, we are pretty well insulated. Looks like it might be an idea to go constant, especially as the kids are back home early most days.

I'll keep myself warm by eating some humble pie too 😆

Insulate the home properly and it won't even be an issue.

What if your house has solid stone walls and despite 500mm of loft insulation goes cold within an hour or two of switching the heating off?

The FIL has plenty of time for things like this and he assures me that leaving the heating on low all day uses far more energy i.e. [i]money[/i] than putting the heating on when required.

In our house, to save money we have no timer set and we have to turn it on with the thermostat if we want it on.

When we are out, its off. When we are in bed its off. We tend to give it short blasts as and when required, we have blankets on the sofas that we get under if we are indoors watching films. The rooms are quite small and heat up quickly.

However....

The MIL who looks after littlelegs during the day, is used to the temperatures in the old peoples homes she used to work in, and has thyroid issues does things differently. Heating on full, windows open, all day, so that she isnt "freezing" but she still has "fresh air"

What can you do

it's cheaper to set your CH to on "permanent" and just drop the room 'stat to 18 while you're out or in bed

But that is turning the boiler on and off, that's what your room stat does. That's different to running the boiler on low all the time. Room thermostats have kind of confused this argument really, because they are somewhere in between leaving it on and using purely a timer.

We set ours to 16 at night and it hardly ever comes on, so effectively we switch off overnight and in the day time.

As for whether you should leave heating actually on all the time, surely obviously not, the warmer you keep your house, the more energy is lost to the outside, so the more energy it requires to heat it. Better to turn thermostat on when you're home (or until just before you get home) and off when you're out. it's as likely to make sense as leaving the kettle on all the time.

No thermostat here, just a timer. I have the heating come on for an hour just before I usually get out of bed, an hour around 5, hour around 9 and half an hour before I usually go to bed. This week I've had it on for large chunks of that day as I work from and my toes are hurting from the cold! I'm fairly sure it's cheaper that way than always having it on low through the day and night.

Simple physics gents. The rate of heat loss is proportional to the temperature difference. You lose more heat by keeping the heating on overnight when it's coldest.

Our cat would vote for "on all the time" I know that much. Too bad for her she can't reach the controls!!

What if your house has solid stone walls and despite 500mm of loft insulation goes cold within an hour or two of switching the heating off?

You insulate your walls.

It's not as hard as you might think. You can do as little as insulation backed plasterboard and skim

Or go as far as 150mm of phenolic board, with plasterboard and skim.

Also you might consider insulating under your floorboards too, and sealing all the big gaps round the edges (you can't see them from above, but they will be there !)

Those two things make a [b]massive[/b] difference.

Where I am staying at the moment is literally freezing. I have the boiler on max at the moment, there is no temperature thermostat, and it's still not warm enough.
The metal windows leech heat like crazy - it feels like they're open even though they're not.
The bathroom is like an ice box, with no form of heating in it - the door is always closed and it never seems to dry out.
The curtains don't fit the windows and are paper thin so don't offer any insulation.
Thankfully, I don't pay the gas bill...

Our heating is off all night after about 10p.m. coming back on about 7a.m. However we don't have it on all day, even though I work from home.
Lots of hot drinks, fleece wearing and a ho****er bottle in our house.

We do have a woodburner though for really cold evenings.

What if your house has solid stone walls and despite 500mm of loft insulation goes cold within an hour or two of switching the heating off?

Simple physics gents. The rate of heat loss is proportional to the temperature difference. You lose more heat by keeping the heating on overnight when it's coldest.

This, think of heat in and heat out as 2 seperate (but equal over say 24 hours) things.

The boiler is pretty much the same efficency whether its running at 100% or 1%.

heat out = (upper case sigma, lookes like E, means the sum of) dt * k * dT (T=temp, t= time, k=constant which will be lower the more insulated you get)

E; i.e. the sum over a time period, you cant change unless your Dr Who, thats just

dt; reprisenting the passing of time (not how long the heatings on for) see 'the sum of' above.

dT is the temperature difference, so keeping the average temperature in the house as low as possible reduces it. So having the heating on overnight is pointless.

So an example.

heating on for 24 hours, dt = 1 hour, k = 1, outside 0deg, inside 20deg.

dT = 20
k = 1
dt = 1

20'heats' lost every hour, so 480'heats' in a day.

Now over a day, with the heating going on and off.
Time, temp, heat lost (calc'd as above, but 2 hour intervals)
6am 20deg 40
8 19 38
10 18 36
12 17 34
2 16 32
4 15 30
6 20 40
8 19 38
10 18 36
12 17 34
2 16 32
4 15 30

Sum of heats lost = 360'heats'

So by only having the heating 'on' twice a day and letting the house cool in the meantime you're saving (480-360)/360*100= 33% on your heating bill.

Obviously the slower the heat loss the closer it gets, a super insulated house would loose no heat and therefore would make no difference.

As tinas says - cheapest is to keep the temperature difference to a minimum, so set time clock to off during the night (& day if house isn't occupied) - then just set the heating to come on before you get up & before you get home so it isn't cold when you want it warm - and prob set it to go off before you go to work / bed. Keeping it trickle warm when not required is just a waste of energy. If its really cold then a frost stat will prevent pipes freezing etc. Thermostatic rad valves are a good way of only heating the spaces you need to heat too.

Oh yes & boiler cycling on & off is not so efficient - most efficient is for it to be going full on to get the house up to temp after an off period

My Mrs says she's having the heating on all the time at the moment like it or not. She's got a west indian bloodline, and I feel the cold. Its 22 downstairs, 19 upstairs due to individual rad thermostats.

We'll worry about the heating bill later, and comfort today (she says).

@ Bunnyhop - you don't consider constantly boiling the kettle using energy?

I'll be back in a minute its time to change into some shorts.

I stick my thermostat at 21 and leave it there, seems to work ok.

What if your house has solid stone walls and despite 500mm of loft insulation goes cold within an hour or two of switching the heating off?

thank yourself lucky your house is not listed, then you would be stuffed... trust me!

thank yourself lucky your house is not listed, then you would be stuffed... trust me!

My physics isn't up to the task but surely thermodynamics means that you can't win. The laymans 3 rules of thermodynamics are:- 1. You can't win, 2. You can't break even, 3 You can't get out of the game.

I get really fed up of asking people at work why they refill the kettle at work and then boil it even if no one is waiting. One guy constantly fills and boils both kettles to make one mug of drink. His argument is time (as is everyone else's). OK company pays but they can't see that if the fuel bills were reduced there might be more money in the pot for the workers. If nothing else why would you want to line the pockets of the energy companies? Forget trying to persuade them on the energy waste POV. Do you really have to be a "greeny" to see that wasting energy is bad?

whilst out i have it set at 10, and when in its now set to 18 after 9pm it goes to 16 until 11 then 10..

Interesting this. We've just had a wood pellet boiler fitted which, being Austrian, has come with some very complicated and sophisticated controls. It took the installer 2 weeks to get it running right because we had chosen to heat the house to 17.5C Apparently this is considered too cold so it had thrown the boiler into 'setback mode' where it worries about maintaining temp and so puts the heating on just in case. Once we settled on 18.5C it's reverted to normal timed operation!

The control does things like monitor the outside temp and anticipates a drop in house temp when the heating is off so will put the heating on so it doesn't have too much load when required to be on by the timer.

I asked how we should turn it off in the summer. The answer was not to - just leave it on and it won't be on because the temp will be high enough. We'll see. In the meantime it's nice to be warm!

Kryton57

@ Bunnyhop - you don't consider constantly boiling the kettle using energy?

Overall you'll have lower energy loss by turning off during the day as your power loss is related to the temp difference between inside and outside. It's complicated by the fact that contact with the interior of the internals of the house (seats, desks, floors) have a thermal time constant significantly higher than the air which means it *feels* colder for longer if you heat up from cold each evening and morning, but it still costs less overall. There's also the point that your boiler may or may not operate more efficiently at max output, depending on type, so keeping it ticking over all day could well be less efficient (or more, hard to tell without specifics).

As I say it's pretty much a fact that it uses less energy to do heat/cool/heat than constant but it depends if that fits with your life and house use. I've been running tests with our house for a long time, which are fairly inaccurate really due to weather differences from day to day, year to year, so really all you can do is accept that theory says it's better to turn it off but unless you come home at the same time every day or are willing to have a cool house until the timer hits, it might be more acceptable to keep it on fairly low.

I've settled on keeping it at 17C overnight and turning it off when at work. Generally it never drops below 16 during the day anyway so having it fire up at 17 would make no sense and we spend about 60 quid a month in gas for a 3 bed semi with half-dodgy insulation in the roof during the winter (90 a month when it was -17 outside for a couple of weeks in a row).

One guy constantly fills and boils both kettles to make one mug of drink. His argument is time (as is everyone else's).

Eh? Takes longer to boil a full kettle?

One guy constantly fills and boils both kettles to make one mug of drink. His argument is time (as is everyone else's).

Eh? Takes longer to boil a full kettle?

He should make drinks for everyone, saves their time, most efficient use of the kettle, well done that man.

you can go nuts on working out efficiency - should I spend £100 fixing the fan in my D rated boiler or spend £600 on a new A rated one... At the moment I'm just hoping it doesn't fail.

All of these plans are easilly ruined by having a GF who refuses to wear a jumper indoors.

My strongest argument for leaving on 24 hours is this: when you turn on the CH after being out all day, the boiler flogs itself for a couple of hours solid. However once it has warmed up the air inside the house and the structure and furniture the room 'stat switches it off and from then on for the rest of the evening it only burns once or twice an hour for a few minutes. The house and its contents become a storage heater and warm contents and structure make for a much more comfortable heat, it also helps to reduce condensation and damp and damp increases the sensation of cold (or heat for that matter).

We went away skiing for a week in January and left the CH on full time with the 'stat set on 15. When we got home it only took a few hours for the house to warm up, whereas in previous years we've turned it right off, come back to a house that's SEVEN degrees C and the boiler has laboured for 48 hours to get everything warmed up.