/ Central heating, on a timer or on constantly?

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Beardyman - on 24 Feb 2013
Hey folks, I was told by an Aunt who also has an old house that it was more efficient to try and keep your house at a constant temperature rather then have it on a timer. Anybody got any thoughts on this?
butteredfrog - on 24 Feb 2013
In reply to Beardyman:

Depends on the construction I suppose. We live in a 200+ yr old stone cottage and it is definately cheeper to leave the heating set to a constant 15deg. Does take a couple of days for the walls to cool down, but let that temperature drop and it takes a good 24hrs to take the chill off.
Philip on 24 Feb 2013
In reply to Beardyman:

I think it that you don't neat the fabric of the building, you basically just heat the air. Better to have the heating on so the air is warm when you get home or get up.
Jack B on 24 Feb 2013
In reply to Beardyman:

I live in old diggs with single glazing. The heat goes out really fast when the heating goes off. Keeping the place warm when I'm at work would break the bank!
sleavesley on 24 Feb 2013
John_Hat - on 24 Feb 2013
In reply to Beardyman:

We are trying that experiment now. We've got a 1930's house which is drafty and leaks heat (ongoing issue we are working on). If the house fully cools down then it takes 24-36 hours to get back to temperature, so we thought we would experiment.

Hence this winter we tried keeping the heating on continuously, and last winter we tried the on-off technique.

More accurately, this winter we heated the upstairs continuously (heating never off but controlled by roomstats), and downstairs was continuously heated 6am-11pm (also controlled by roomstats).

TRV's on all radiators.

Anyways, we got the gas bill for the winter a couple of days ago, and the result appears to be that it's about the same to heat the house continuously rather than on-off, however its *certainly* more pleasant to be in a house at a constant (warm) temperature. This rather surprised me as its counter-intuitive that on all the time is the same.

Total energy used for both winters (Nov-Feb) was around 15000 kwh.
Jim Hamilton - on 24 Feb 2013
Blue Straggler - on 24 Feb 2013
In reply to John_Hat:

Thanks John for doing the experiment and reporting it. I am in a similar situation though not a similar house, mine dates from about 1810 and the cold has different causes to just draughts, but I've often pondered what would happen if heating were left on constantly...but never done the experiment.
Clint86 - on 24 Feb 2013
In reply to Clint86: We just keep one room warm in the winter, a bit like the old days. Works fine for us.

Trangia - on 24 Feb 2013
In reply to Beardyman:

Constant. I control the heating with the room stat in the hall.
Orgsm on 24 Feb 2013
In reply to Beardyman:

Our heating never really goes off, or n timer. It has a modern controller. You can set the temperature to be maintained at certain times if day, and by day of week. So you have complete control, keep it high all time, or allow to dip a little during day, or hotter during day, cooler at nigh etc.
Mark Morris - on 24 Feb 2013
In reply to Beardyman: A few years ago we hung thick curtains on rails above the front and back doors. Even in a house built in 2000 I'd noticed the chilling effect of draughts around the door. Our first "sum up" of our gas bill for the year showed significant savings during the really cold winter we had.

Interestingly, we've had cavity fill since and the gains since the curtains are marginal - the house was already well insulated, air change/draughts being the biggest cause of heat loss.
Robert Durran - on 24 Feb 2013
In reply to Beardyman:

Theoretically, allowing the house to cool down when you are not there and then heating it up on a timer for when you are at home should be more economical since the rate of heat loss (which therefore needs replacing) is lower when the temperature difference between the inside of the house and the environment is lower.
Beardyman - on 26 Feb 2013
In reply to John_Hat: Thanks for that, saves me doing the same!

I have good double glazing and loft insulation but as house was built around 1800 there is no wall cavity, just thick walls, and no underfloor cavity either.

Last year heating (and hot water) cost 189 per month!!

I'm considering just heating the living room and putting more blankets on the beds!!!
Liam M - on 26 Feb 2013
In reply to Robert Durran: That may not always be the case. If you have an atmosphere that has settled into an approximately quiescent state your heat flow through the walls may be smaller than if you introduce a relatively large heat source into a much colder enclosure that results in a more 'active' flow (higher Rayleigh number).

My thought would be it would vary from case to case and would depend upon the relative magnitude of the heat flow through the wall and the strength of the convective flows within the room/house. It may be that houses always fall into one category (I've only ever worked in dimensionless parameter space so have little feel for practical magnitudes) but I don't believe the theory always points to one case.
EeeByGum - on 26 Feb 2013
In reply to Beardyman: We have a pretty well insulated 1970's house. We used to just have the heating on in the evening and first thing in the morning, but my son kept waking up cold so we now also have the heating on through the night. I believe the boiler only actually kicks in twice usually for about 10 minutes at a go. I certainly think on-all-the-time has many positive merits, but you need to be well insulated in the first instant.
DancingOnRock - on 26 Feb 2013
In reply to Beardyman: We use an unoccupied set back approach. When at home the stat is at 20'C, when we go to bed or go out we turn it down to 15'C. Also have thermostatic rad valves.

This means on warm days you're not trying to heat the house so far up above outside temp.
Jim Hamilton - on 26 Feb 2013
In reply to Liam M:
> My thought would be it would vary from case to case and would depend upon the relative magnitude of the heat flow through the wall and the strength of the convective flows within the room/house.

According to the link above it seems it's more about condensation in the walls reducing their thermal efficiency when a house is allowed to cool down, and the heating on all the time approach won't work if it's draughty.
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a lakeland climber on 26 Feb 2013
In reply to DancingOnRock:

20C? That's a f**king sauna! Ours is on 16C for an hour or so in the morning to take the chill off then for about 4hrs in the evening.

ALC

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