please empty your brain below
It will be interesting to see how the comparisons work across the warmest part of the year.

In winter I curse the seeming energy inefficiency of my home but in the summer it is a blessed relief that the house remains resolutely cool despite the sometimes searing heat outside.

Mel | 13.05.21 - 7:08 a.m. | #

Mel - maybe your house is designed for the tropics! 45 degrees, anyone?

anon | 13.05.21 - 7:15 a.m. | #

I've always wondered whether less energy is used if the central heating is on or off overnight. So for several months over this winter just gone, I did an experiment.

We're wimps and so we like our house to be at 22 degrees during the day. Overnight I programmed the Nest thermostat to be 22, 18 or 10 degrees (which effectively means the CH is off all night) from 11pm on different days of the week. I then told Nest to do whatever it needs to do to get the temperature back to 22 degrees by 7am (it has some intelligence and can work out what times the CH needs to be turned on in order to do that).

Nest allow you to retrieve lots of information from the thermostat. As a proxy for the amount of energy required to get the temperature to 22 degrees by 7am, I extracted the number of hours the CH was on between 11pm and the time that the temperature hit 22 degrees after 7am (it was sometimes late).

Averaged over several months, the least energy was used if the thermostat was set to 22 degrees overnight. The most was used if it was set to 10 degrees - 30% more as compared to 22 degrees.

Our house is insulated fairly well within the limits of what you can do in a 1908 mid-terrace house. We have a combi boiler that's about 8 years old.

Regards

zin92 | 13.05.21 - 7:20 a.m. | #

Interesting, although I think that the humidity is just as important, humid hot is debilitating, dry hot is survivable, humid cold steals the heat from your body, dry cold doesn't.

I don't like rooms too hot, although the NHS advice has the optimal temperature around 21C for the living room and 18C for the bedroom, but I'm currently in the living room at 16C and I'm quite comfortable.

Still Anon | 13.05.21 - 7:41 a.m. | #

I never switch my central heating off, I rely upon thermostat control. So get a cold day in June and the heating comes on. I keep my bedroom at 21c.
If we get a hot summer I also have installed aircon which cools the house down. By the way the aircon units can also work as heaters and are quite efficient when used that way so I may use them for heating and cooling when the gas boilers start to be phased out.
I cannot sleep in a cold room, and even if a duvet keeps your flesh warm you are still breathing in cold air.

John | 13.05.21 - 8:10 a.m. | #

I've also subscribed to the theory that heating 24hrs a day works better, or at least saves so little as not to be worth the discomfort. What I've noticed is that the walls feel warmer, and as they have a higher specific heat capacity than air, hold heat better. This just makes the whole place feel better. The higher shc also means they suck heat from the air as you're trying to bring that back up to temperature.
Also as another poster says, the idea of the thermostat is to control the temperature automatically, so why switch the heating off in summer manually?

Putters | 13.05.21 - 8:17 a.m. | #

Do you ever open windows (or balcony doors)?

Ian | 13.05.21 - 8:24 a.m. | #

I stand to be corrected on the physics but it has always seemed to me to be a simple answer to the question about whether to keep the central heating on continuously. A property has a given propensity to lose heat if it is warmer than the outside. The greater the temperature difference between the inside of the property and the outside, the greater the heat loss. So to minimise heating costs, don’t heat it above the temperature needed at any given time.

J. | 13.05.21 - 8:32 a.m. | #

If I lived with someone who insisted the heating was on 24/7 I'm pretty sure it'd end in divorce.

Mark | 13.05.21 - 8:56 a.m. | #

I suspect there are a lot these days who leave it to the clever sort of thermostat. Ours is not anywhere near as clever as a Nest, but still has 8 times a day you can set a temperature for every day of the week. And that wasn't a particularly high-end option when it was installed 10 years ago.

FWIW, I set it to 20 during the day, 16.5 at night - or at least while I'm still home all day. Daytime is lower at the weekend as either we're likely to be out, or all three of us are in to warm up the space with our bodies. This is with cool in summer, warm in winter concrete walls.

Chz | 13.05.21 - 9:01 a.m. | #

Wow, don't people live differently. Our (mechanical) boiler timer broke 20 years ago, and though I found another in a bin, I never fitted it. This means no-one can set it to come on in the morning (for the 1/2 hour we're running around before being out all day anyway) and in the evening its coming on is a matter for...errr...debate. I'm not sure the thermostat works any more either - though it still goes click in that way I remember from childhood - the reassuring click as my Dad turned it down which told him that all was right with the world, as the broken clock reassures me now.

mark addy | 13.05.21 - 9:27 a.m. | #

zin92 - either your house is breaking the laws of thermodynamics, or your Nest is not quite as intelligent or as accurate a proxy for the energy used heating your home as you think it is. I'm inclined to suspect the latter.

James | 13.05.21 - 9:40 a.m. | #

Having had our downstairs neighbors move out during the winter and our new ones only just moved in I now realise how much we benefited from our neighbors providing under floor heating!!

kerspatula | 13.05.21 - 9:56 a.m. | #

The previous commenter has made the point I was thinking of writing.
In flats you can get a lot of benefit from your neighbours' heating. If the flat below is keeping their flat very warm it must make a big contribution to keeping the flat above at a comfortable temperature.

Martin | 13.05.21 - 10:23 a.m. | #

Another dimension to add is the effect of indoor temperature on how much you move about. I find that I'm much more likely to get up from time to time and do something active if the indoor temperature is cooler. As 21 or 22, armchair based activities seem to prevail.

Malcolm of Kent | 13.05.21 - 10:48 a.m. | #

Hi James.

Nest tells me how many minutes the heating was on for in a given time period (and I can't see why this wouldn't be accurate). As the boiler heating is either fully on or fully off, I therefore thought that this would reflect how much gas had been used for heating.

Are you surprised by the results I got and therefore think that my calculations are wrong? I must admit that I was surprised that leaving the heating on overnight seemingly means that less gas is used.

Thanks

zin92 | 13.05.21 - 10:53 a.m. | #

I'm another one who doesn't turn the CH off year round, but uses the thermostat to control it.
It's programmed to be about 18C during the day when we're more active, 21C in the evening when we're more sedentary and 13C overnight.

The house always feels too cold during the winter and too hot during the summer.
It's only when coming in from outside that you realise just cosy/cool it is in comparison!

Cornish Cockney | 13.05.21 - 11:13 a.m. | #

"Don't say you're surprised."

Oh, thank you dg. Laughed out loud at that moment!

Gareth | 13.05.21 - 12:37 p.m. | #

I have a Tado controller which tracks when we are away from home and turns the heating on or up when it sees us heading back. It calculates that that tactic saved us 13% on our gas bill in the last year - when we've been at home much more than usual.

Peter | 13.05.21 - 12:41 p.m. | #

A couple of points:
1 I'd be with James on the seeming impossibility of zin92 using less energy with his heating turned on, except that a friend once opined that tea cosies were invented when china teapots replaced silver ones because the china lost heat more quickly than the silver. I, of course, pooh-poohed this knowing that a container made of a thin metal with excellent heat conducting properties would loose heat faster than one made of a thicker, poorer conductor of heat. To prove my point we found two similar teapots of the two materials, filled them with similar quantities of boiling water and waited. Inevitably the china one cooled more quickly. I can only assume because heat loss by radiation exceeded that by convection. So I am now more cautious of pontificating.
2 Has anyone else noticed that with central heating thermostat set at the same temperature it seems more difficult to feel really warm indoors when it is colder outside?

RogerB | 13.05.21 - 12:52 p.m. | #

Hi James, RogerB,

Just to make sure that there's no confusion, I'm comparing the gas used to maintain the overnight temperature at a constant 22 degrees with that which would be used to bring the house back up to 22 degrees by 7am if the heating was turned off at 11pm.

With the former, the heating would need to come on briefly several times during the night (every time the temperature dips below 22 degrees). With the latter, the heating would need to come on for one extended period (the length of which would depend upon how cold it's got in the meantime) prior to 7am.

Regards

zin92 | 13.05.21 - 1:11 p.m. | #

As this is turning into 'me and my heating system' I will just note that I bought a more expensive boiler just so that I could have a clicky analogue timer rather than a digital one that I knew it would drive me mad to try to programme. And being tucked up snugly in a cosy bed whilst breathing cold air is one of life's great pleasures.

Sarah | Homepage | 13.05.21 - 1:18 p.m. | #

I'm one of those people who never puts the heating on, even in winter I can go outside without a jacket on

Rachel | 13.05.21 - 1:43 p.m. | #

Hi zin92, yes, I understand what you're comparing, but it does seem strange that the house apparently looses less heat (measured by how much energy it takes to re-warm it) when it is kept at the higher temperature.
That's why I mentioned the teapot example, there may be something else going on other than than simple conduction of heat out through the walls and roof.

RogerB | 13.05.21 - 2:18 p.m. | #

This is why I read DG every day!

Started reading years ago to find out about interesting places in London, but stayed for the random subjects that come up and make me ponder a bit.

I also enjoy the interesting debate in the comments section too, and today's has been really good.

Peter of London | 13.05.21 - 2:19 p.m. | #

Brick will conduct heat differently depending on moisture content. So, if the heating's kept on, this will dry out the bricks, causing them to insulate more effectively.
However, I cannot abide duvets, and two conventional blankets are sufficient with no night heating in the cold months.

Nick K | 13.05.21 - 10:03 p.m. | #

As others have suggested, 'keeping the heating on all night' doesn't mean it's actually on all night, but only turned on as required by the room thermostat. A sophisticated controller/monitor can probably tell you how long the boiler was actually running each night, compared with how long it takes to bring things up to temperature after being off all night.

Keeping the heating ticking over all the time is certainly a good way of reducing condensation in a property, which thrives on cold walls.

ActonMan | 14.05.21 - 10:07 a.m. | #

Since your thermometer is on an outside wall near the window, it will most likely be cooler there than in the areas of the flat that your body actually occupies.

So, although you say you can tolerate 15C, I'd want to see data from further away from the window before I believe it.

PBak | 14.05.21 - 12:34 p.m. | #

Sorry, I should've recorded the temperature on my other thermometer further from the wall/window (which is usually ½-1°C warmer than the thermometer near the outside wall).

Rest assured I can tolerate 15°C.

diamond geezer | Homepage | 14.05.21 - 12:52 p.m. | #

>>>observe the effect of outdoors on indoors

Excel can graph both to show relationships, lag, phase, etc

If a common date/time is in 1 column, and indoor and outdoor temperature in 2 more columns, then a new graph...

X-axis=indoor temperature
Y-axis=outdoor temperature
Type=XY(Scatter), with lines

Gives ellipses, swirls and whorls

Good fun, but in practice, with short term weather data, my experience is that your 2 separate time graphs, plus eyeball+brain, give better insights.

Kate Demontration | 15.05.21 - 3:37 a.m. | #

Zin92 - why not read the gas meter? I think you are using the time that the heating is turned on as a measure of how much gas is used. I have argued with a couple of people who thought that "heating every room in the house makes no difference to the bill". My answer to you is to suggest a thought experiment. Imagine that you are on holiday for 3 weeks. Would it be cheaper to turn the heating off or leave it running at 22 deg C? Now reduce the holiday time to a couple of days and ask yourself the same question... Now overnight...

Kate Demontration - your suggestion beat me to it. The data part of me suggests that there has to be a better way of plotting the correlation than trying to follow the undulations of two lines, though.

Half a physisict | 15.05.21 - 8:28 a.m. | #

It's not been back to 18°C since.

diamond geezer | Homepage | 24.05.21 - 7:33 a.m. | #











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