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Is it more economical to turn the heat off during the day when out or leave on?

Discussion in 'Renewable Energy & Energy Saving Forum' started by TurnipFarmer, Nov 24, 2008.

  1. TurnipFarmer

    TurnipFarmer Member

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    Guys

    You may have seen the question before and as it is starting to get cold what is best for cost in energy bills and efficiency, best to turn off heating when no one is in and then turn it on when you get in or is it best to leave the heating on when out but at a lower temperature and then just turn it on when you get back in?

    What are you views on this and what are the best temperatures?
  2. eric pisch

    eric pisch Active Member

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    depends on the house

    when i was studying to become a chartered surveyor, we spent some time doing thermal loss calcs etc on different types of construction.

    the logic goes like this it takes a period of time for the heating to heat up the fabric of the building during this time the heating system will have to work harder, once the fabrics there the heating system should just tick over to maintain a set temperature.

    some older houses (solid wall) could take a couple of days to reach this level, modern houses maybe a few hours. The amount of heat lost is also critical, if in "tick over mode" the boiler has to run as much or nearly as much as the initial stage then its better to turn it off when out.

    if the house has good insulation and does not have lots of space you dont use then its better to leave it on when the temp drops to say 4 or less outside. A digital thermostat works well with this as you can reduce the temp 3 or 4 degrees at night or when your out without cooling of the fabric to much.
  3. robh2002

    robh2002 Member

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    The answer is _always_ to turn the central heating off when you are not in and on again when you are home (or timed). The reasons is if you have it on, even a few degrees lower, you are continuing to maximise the difference in temperature between outside and inside the house - and therefore maximise the heat loss. Insulation only slows this down - so you should still turn off!

    It is true that the heating will have to work harder (i.e. put out more heat) when it is commanded to come on again, but it will always use less energy _overall_ than if it was on all the time, even at a lower heat. A number of friends switched to this method and confirmed it does lower their energy consumption. Try it - read you gas meter over a few days (making sure the outside temperature is actually the same!) and you will see.

    Hope this helps. And spread the word as this comes up again and again!
    Last edited: Nov 24, 2008
  4. eric pisch

    eric pisch Active Member

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    not always true thou im afraid, you can do the calcs, the house type is critical thou, I leave mine on and my monthly gas consumption is 5-10% less, but i have a new small energy band A house.
  5. robh2002

    robh2002 Member

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    Sorry, but it is always true if you heat as I suggest! If you consider the heating to be steady - which is what you are saying, you are right - but that is not appropriate for the heat only as required method.

    The explanation is as follows: If one heats only as required and not continually, the fabric (i.e. brick/block/cement etc.) of the house may never get to a fully steady state temperature. This means you minimise heat loss. However, we perceive the air temperature within the house and this heats up faster and so we get the warmth and comfort required. What it boils down to is the ratio of specific heat capacities of the air in a building to the fabric of the building - and air has the significantly lower value! The air heats up significantly faster than the building fabric. Incidentally, this is why it is best to insulate on the inside of a wall - although this is obviously not always practical. Again, this is only if the house is heated as required. If the heating is on all the time, then again, insulation anywhere will do the same job.

    Clearly there is a limit - if one has the heating off for only an hour a day, then this will make little difference to the overall energy required so there is probably no point in heating as required.

    So as I mention, steady state calcs/arguments will show you to be right, but the whole point is if you heat intermittently, you will minimise heat loss and lower your bills.
    Last edited: Nov 25, 2008
  6. ps3mad

    ps3mad New Member

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    I never have the heating on,not because im tight but because i cant stand the heat.I love the winter and hate the summer.The question for me is electric cost as i have the aircon on all the summer and that cost a fortune.Im sitting here now in my shorts(not a pretty sight lol)with the windows wide open mmmm nice! :smashin:
  7. Marc

    Marc Active Member

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    i tend to turn the heat on half an hour before i get home from work and have it on for 4 hours or so.. doesn't do a damn thing though, i have to sit on the radiator to notice the heat so i had been thinking about putting it on permanently, but its a risky experiment with the gas bills already pretty high (£40 a month) and i dont think with my cold brick walls and single glazing that my house would ever reach the level the thermostat is set to (22)

    it'll probably work out cheaper to leave the heating off and just put my pc and xbox 360 on all the time instead :D
  8. robh2002

    robh2002 Member

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    Obviously I'm not sure what sort of radiators you have, but newer ones tend to be far more effective (not efficient!) so changing a few of those could help a lot and it is not very expensive - if you are happy do do the plumbing yourself. Secondly, are the radiators sized for the rooms correctly?
  9. Marc

    Marc Active Member

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    i'm renting :D no changing of radiators for me i'm afraid.
  10. robh2002

    robh2002 Member

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    I see the problem! Foil behind the radiators? - fans underneath? - perhaps using that plastic film to form secondary double glazing?
  11. Marc

    Marc Active Member

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    does that window film stuff work well? I thought about it in my last flat (why don't i get somewhere with double glazing???) but must admit i haven't really thought about it in a while.. i have a single glazed bay window taking up about 2/3 of the front wall..
  12. robh2002

    robh2002 Member

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    I've never used it - and I would be concerned about condensation forming on the inside. But I should imagine it would provide some additional insulation - but I've not seen any proper numbers on it.

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