Energy myth-busting: Is it cheaper to have heating on all day?

Swipe

My immersion heater is permanently off and only goes on 1 hour before a bath but I'm not on E7

r2015

How much electricity is needed to heat a 150 litre hot water tank from cold, approx. 12 deg C to 80 deg C ?

torbrex

I have gas central heating but no radiators, I get instant heat as soon as the heating is switched on so its a definite no from me, no, it is not cheaper to leaving it on all day, there is no point in heating an empty house.

HappyMJ

r2015 wrote: »

How much electricity is needed to heat a 150 litre hot water tank from cold, approx. 12 deg C to 80 deg C ?

Water in a hot water tank is usually near room temperature. Maybe 18 deg C. 80 deg C is very hot you might only need 70 deg C.

Using your figures though.....

4.186 J * 150,000 grams (of water in 150L) * (80-12) = 42,697,200 J

Convert that to watt hours and you get 11.86kWh. You'll need a 3kW immersion element on for 4 hours to heat 150 Litres of water from 12 to 80 deg C.

Change the figures to my figures of 18 to 70 deg C and it reduces it to 9kWh so only 3 hours of the immersion to heat from cold.

Most of the time there is left over heat from the previous heating session and the average water temperature is 40 deg C (60 deg C at the top half and 20 deg C at the bottom half) so only 2 hours is needed to reheat the cylinder.

And...if you use no hot water over 24 hours the average temperature of the whole cylinder would have fallen to around 60 deg C and would require 1.75kWh or about 35 minutes to reheat it back to 70 deg C which is your standing losses.

Superscrooge

Energy myth-busting: Is it cheaper to have heating on all day?

After reading all the arguments over the last few years about whether or not it is cheaper to leave the heating on all day there seemed to be convincing arguments for both points of view,

So last winter to satisfy my curiosity I decided to conduct my own experiment for a couple of months in January/February to see which came out cheapest for me..

For eight weeks each Sunday evening I read the gas meter and then the first week I just had the heating on when I was at home, the second week I additionally kept the heating on low all day. I alternated each week for eight weeks. I alternated weekly rather than a monthly to try and minimise any effect of a particularly cold month.

The amount of gas used as you might expect varied quite a bit from week to week because of the changing outdoor temperatures, but even with the changing outdoor temperatures the result for me was absolutely clear-cut. The four most expensive weeks were when the heating was left on low all day and the four cheapest weeks were when the heating was only on when I was at home. On average I was using nearly 20% more gas keeping the heating on low all day.

I realise some contributors on here are convinced it is cheaper to leave the heat on all day and can produce good arguments to that effect. I am also aware that a flaw in my argument might be that the weather just happened to be colder during the weeks when the heating was on 24/7, although I don't believe that was the case.

So for me this winter the heating will only come on when I need it as this appears much cheaper than leaving it on all day.

I don't expect that will be the end of the argument !!!

tronator

wattsupnow wrote: »

Take a look at my video on YouTube: Home Heating: How the Market is Rigged to Favour Gas.

Ripped out our unreliable and noisy GSH years ago and fitted Dimplex Panel Heaters to every room. Chose their budget panel heaters range (not storage) cheap-and-cheerful and does the job.

We are retired, so leaving the heat on 24/7 suits our lifestyles. Switch them on in October and off about April. Annual costs about £800 for heating and hot water plus about £450 for everything else electric in the house 100% reliable, no maintenance or repair bills. A fit-and-forget solution to heating that keeps the whole house cosy 18-22C all day, every day.

I tried fitting timers to every heater to switch off during the night but honestly made little difference to the bills and not worth the bother.

As Richie already said, you're comparing apples with oranges. You should have compared gas and electric both in your well insulated house. Also, it's not true that gas heating works only with one thermostat. You can have thermostats in each room which control the heating in each room independently. I guess the whole system is then controlled by the amount of water flowing through the pipes.

gadgetmind

Superscrooge wrote: »

I don't expect that will be the end of the argument !!!

Empirical evidence that backs up solid theory based on real physics, no, I'm guess that won't convince everyone!

malc_b

Superscrooge wrote: »

Energy myth-busting: Is it cheaper to have heating on all day?

After reading all the arguments over the last few years about whether or not it is cheaper to leave the heating on all day there seemed to be convincing arguments for both points of view,

So last winter to satisfy my curiosity I decided to conduct my own experiment for a couple of months in January/February to see which came out cheapest for me..

For eight weeks each Sunday evening I read the gas meter and then the first week I just had the heating on when I was at home, the second week I additionally kept the heating on low all day. I alternated each week for eight weeks. I alternated weekly rather than a monthly to try and minimise any effect of a particularly cold month.

The amount of gas used as you might expect varied quite a bit from week to week because of the changing outdoor temperatures, but even with the changing outdoor temperatures the result for me was absolutely clear-cut. The four most expensive weeks were when the heating was left on low all day and the four cheapest weeks were when the heating was only on when I was at home. On average I was using nearly 20% more gas keeping the heating on low all day.

I realise some contributors on here are convinced it is cheaper to leave the heat on all day and can produce good arguments to that effect. I am also aware that a flaw in my argument might be that the weather just happened to be colder during the weeks when the heating was on 24/7, although I don't believe that was the case.

So for me this winter the heating will only come on when I need it as this appears much cheaper than leaving it on all day.

I don't expect that will be the end of the argument !!!

Nice experiment. You don't say if your boiler is condensing or not. That makes a difference. Old style boilers cheapest is shortest on time. Condensing boilers cheapest is keeping on time short as long as you stay in condensing mode (i.e. have a low water temperature set). When the weather turns cold and you fail to get a warm house then increasing the on hours is cheaper than increasing water temperature and going out of condensing mode.

gadgetmind

malc_b wrote: »

When the weather turns cold and you fail to get a warm house

That's when you need to start doing more insulating.

Mind you, despite being in our house for 20 years, we're still not 100% double glazed, but we change the windows as we do major renovation to rooms.

lstar337

schiff wrote: »

Thank you for that!

(1) I'm not sure there is any, the outside seems to be bare metal.

You should insulate it, put a jacket on and it will make a huge difference to your bill.

schiff wrote: »

(2) It is always comfortably warm in the small room/cupboard the tank is in; I put towels etc in there when I leave, to air. The door is usually shut at all times.

This would probably change if you insulated your tank, but then there is no need to keep that room warm if you are not in it.