Heating on low and constant better?

albertross wrote: »

This is getting silly. The issue is what exactly?

Read the thread again?

If a house doesn't lose heat through the walls/roof/windows, why do you have to heat it at all? Why is the bill much higher in winter? You apparently have a 100% efficient boiler somehow constantly running in condensing mode, and 100% efficient insulation, the sun is still there during the day, so why is the heating on?

In case it gets cold. Even zero carbon passive solar houses have some kind of heater, just in case. The bill is much higher in winter whether you switch it off for part of the day or not, so it isn't relevant. The question is whether during cold snaps, when it makes any practical difference at all, the savings due to turning the heating lower outweigh the cost of not messing about with timers all the time. I say the savings from setting timers is negligible over a whole year. You have to convince me that a decent saving is a) acheivable and b) the default scenario.

You can mention thermal mass, the sun, and flue loss all day long, but it won't change the simple fact that the reason your boiler uses more gas to heat the house in winter, is because it's heat escapes to a colder atmosphere, the bigger the difference in temperature, the faster it goes.

Where did I ever deny that? Go on, quote me. The issue is how fast does it lose heat? It's relevant. The house still loses heat, even if you only switch the heating on for intense bursts. That's how it works when it's on anyway. Or are we talking at cross purposes here and you're actually advocating turning the heating off completely and shivering all winter? It will save money, but most people wouldn't go that far.

kettricken wrote: »

My goodness - I started reading this thread because I was wondering what other peoples findings were regarding timer switch used or leaving on constant. I have now decided that I will conduct my own experiments and use my own findings. I don't give a damn about the relative temperatures etc, I will base my findings on gas used + comfort. I will not post my findings because I think there are too many picking holes on this thread...............

Well you did ask and it won't be long before the question gets asked again!

mech wrote: »

Read the thread again?

In case it gets cold. Even zero carbon passive solar houses have some kind of heater, just in case. The bill is much higher in winter whether you switch it off for part of the day or not, so it isn't relevant. The question is whether during cold snaps, when it makes any practical difference at all, the savings due to turning the heating lower outweigh the cost of not messing about with timers all the time.

Aha, we're getting somewhere now. The critical point will be the moment in time when the house with timers cools to a temperature lower than the house with the heating on all of the time. If the timed house does fall below the 24/7 house then it will be cheaper to heat the timed house. If it never falls below the 24/7 house then the 24/7 will be cheaper to heat.

If I were to put you in a house that was heated to 20deg C at 9am and then turn the heating off for 8 hours do you think you'd feel cold by 5 o clock?

SP1 wrote: »

I have been following this topic with intent ( My Previous post / the whole topic) It is what works for you, to be warm and comfortable at a cost you are happy with.

I think that sums it up nicely!

Like many things, the temperature you have in your house is a compromise between comfort and cost - and in my book, comfort wins every time.

I think all the 'on a timer' advocates have ever said is that cheaper to turn heating off when you leave the house(be it for an hour, a day or a month!) or when it is not needed e.g. you are in bed.

albertross wrote: »

I did consider having a category for you and one other person who's POV is contradictory, but couldn't decide what to call it, and didn't want to single anyone out, so that was my best shot.

Fair enough.

Look through the thread again, and you will find 30% quoted savings, and somewhere amongst these threads, half was mentioned.

Those kinds of figures are simply unobtainable in my house. That's on a day-to-day basis, let alone across a whole heating season. I would say maybe a 10%-15% saving is possible over a whole winter with a conventional boiler. With my condenser I think the losses of going against its performance characteristics would cancel any gains. I can see how running on a timer could theoretically produce a loss.

People including myself have tested it, and found the same result as the science suggests. (I don't remember the figures, but it was significant).

As already discussed, any home based test isn't going to be at all scientific or rigorous, so if someone gets a skewed result because of bad methodology, that could end up costing them a lot of money over the years.

Interesting. So a test that comes up with the "right" answer is OK, but if we don't like the answer we can call it wrong? There's no reason why a home based test can't be "scientific". Surely a real-world test is more valid, not less. Only the conclusions drawn can be unscientific, not the data.

Also, as already discussed, every house is different, so no organization can predict how much you will save.

That seems fair enough, but figures are quoted for all kinds of other energy saving measures. To not quote typical figures suggests no one's actually researched it.

In the northern states of the USA they seem to have a "triple 8 rule". If you can reduce the temperature in the house for 8 degrees F for 8 hours you reduce your heating bill by 8%. A rule of thumb that can't possibly apply to everyone, but at least it gives you some idea of the big picture. But the UK's climate and housing stock are very different, so it's hard to apply that rule of thumb to both Illinois where it might never go above freezing point for 3 months of the year, and here in North Manchester where if it goes below freezing point at all that's bloody cold, -10 degrees C is unheard of and most houses are >70 years old and of brick construction.

But one thing is for sure, when your heating isn't on, the cost is minimal (pilot light), and if you aren't in the house, you won't notice.

The heating might not be on, but the house is still losing heat at the same speed when it switches off as it did a moment beforehand and continues to lose heat when you're out or asleep. Then you pay for a load of gas to replace what leaked away. The saving comes from the lower rate of heat loss as the temperature difference between indoors and outside reduces compared to when the heating was on. If this figure doesn't exceed the loss in efficiency of running a condensing boiler hard to heat the house up quickly again, no saving is made.

Trial and error suggests this happens for an outdoor temperature of approx 8 degrees C for my house. Ie: When it's 8 degrees C or above outside, there's either a small loss, or no saving in switching the heating off for 16 hours in every 24. When it's below 8 degrees C there's a saving. I can see how this could lead to a net loss over the heating season given the British climate. (This is only a guess - I didn't see much point in determining this intersection accurately as I'm having double glazing fitted next week which might have an effect on the break-even point.)

When I get a round twit I'll bodge together a box linked to an external sensor that overrides the timer when the outside temperature rises above, say 10 degrees C, and shuts off again when it falls below 7 degrees C, for instance. A scheme like this should exploit the best of both worlds.

Oh dear, look how much I typed. I seem to have had a case of textual diarrhea again.