MERGED: Should heating / water be left on?

trafalgar_2

In my opinion it's cheaper to leave it on but you can save a little by turning the thermostat down a touch.........it's often set higher than necessary

Graham1

I also think the 17p/year value is far too low. Most typically lagged hot water tanks cost about £5-£15 a month in electricity to maintain their temperature (from the heat loss), when the central heating is switched off - and that is before any hot water is actually used. Obviously it varies a lot by size and amount of lagging.

So theoretically one might be able to save a reasonable proportion of that, provided the house is not on Economy 7 electric. To get a good saving one would have to be able to predict how long to put the imersion heater on for, so as to heat just the correct quantity of water, since any left over would still suffer the heat loss while waiting to be used and need to be reheated for next time.

Fran

Boardguide comment:

I have merged similar threads which I hope will be useful

bestyman

All the calculations on heat loss assume a tank full of hot water constantly.
When my immersion was on a timer it was set to go off at 11pm. At this time I would get a bath and use all the hot water so the cylinder would be full of cold water and I would get no heat loss untill the timer came on again at 5pm ( im out all day and could wash in lukewarm water in the morning)

So in my case I had heat loss for 6 hours not 24 which must mean 75% less heat loss than leaving it on constantly.

Can anyone dispute that?

Paul

refusnik

There fundamental fact is that it takes the same amount of energy (=money) to heat up water (or any other stuff) disregarding whether you do it slowly or very quickly. Exactly the same!

However there is a constant heat leakage to the outside and that is where things get practical and interesting. In simple terms because heat flows from hot to cold, it takes energy and money not only to heat things up but also to keep them warm. First of all heat loss is proportional to the temperature difference between the water and outside. So if the outside temperature is 20C, it takes twice more energy for the same boiler to keep water at 80C (60 degrees over 20) than at 50C (30 degrees over 20). However the easiest way to reduce this cost is to simply use better insulation!

So energy saving really is about:
1. Consumption - use less hot water. Heat literally goes down the drain! Don't boil the full kettle for one cup of tea.
2. Insulation - insulate hot water boiler itself, insulate the house (drafts, etc)
3. Timing (why keep the house/water hot if you are out?)

refusnik

bestyman wrote:

All the calculations on heat loss assume a tank full of hot water constantly.
When my immersion was on a timer it was set to go off at 11pm. At this time I would get a bath and use all the hot water so the cylinder would be full of cold water and I would get no heat loss untill the timer came on again at 5pm ( im out all day and could wash in lukewarm water in the morning)

So in my case I had heat loss for 6 hours not 24 which must mean 75% less heat loss than leaving it on constantly.

Can anyone dispute that?

Correct, but I have an alternative! If you were paying less during the night hours (like me) it would make much more sense to switch it on at 5am when the unit price is 3-6 times less, heat it up fully and switch off again at 8am when the unit price goes up 3-6 times. You'll get more savings on lower cost of heating the water itself then reducing cost of keeping it warm. The cost ratio is something like 10:1! I was amazed that the heater can stay reasonably hot for nearly 24 hours!

SCRIBES

I have a combination boiler which when it gets really cold I leave on at a low temperature 24/7. When it gets a bit warmer I set it to come on in the morning and evening only. My wife swears blind that leaving it on 24/7 is the cheapest option. I'm still confused despite all the useful messages. Is it cheaper to leave it on at a low setting, rather than having it come on twice a day. Left it on constant last year and got a big bill!, there again prices have been rising! Can anyone give a definitive answer?

shays_mum

Well if its on regardless of how long, its going to cost you.

SCRIBES

Thanks Shay's Mum for your words of wisdom! Of course it is going to cost me, if it didn't I would be surprised and I am sure that it would be a hot topic on this forum. :T What I was asking, was is it more economical over a period of say two weeks to run the heating 24/7 on low constant or to have it set to come on at a higher temperature twice a day for say 8 hours.

rubix_76

islandman wrote:

This is an argument my wife often persues so I will watch and learn with interest. Also, she will often tell me NOT to constantly switch off lights as this can cause "surges".

Your OH is partly right. a 60w bulb does have a slight surge when it is turned on but (and don't quote me on this) it probably only equates to a few minutes worth of electricity (if that).

BUT, a flourescent tube DOES have a much larger surge (I won't go into the physics) and so it is much more cost effective (they are approx 40w compared to 60w, but much brighter per watt) to leave a tube on unless you won't need the light for at least a few hours.

This is why these new (ish) energy saving light bulbs not only use less power when they are running (most are only 9, or 11 watts), but because they are effectively small flourescent tubes coiled up really small, they too are best left on most of the time.

I have energy saving bulbs only in my hall-way and landing as these are traveresed mostly. They are good for outside lights if you want to leave them on all night too. They are however not cost effective to keep turning on and off like the loo or bathroom.

BUT (yep another one) you CANNOT use these energy saving bulbs on light dimmers as a dimmer changes the voltage applied to the bulb to make it, well ..... dimmer, but an energy saving bulb needs all 240 of those little volts to fire it up (most flash a few times when you first turn them on like a normal flory tube).

Well don't I sound really boring (please don't answer that). :rotfl:

Anyhow, I hope this will be of use to some of you peeps)

Rubix