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In this day and age where people are constantly being told to save energy to help reduce global warming etc. I have heard many people ("experts" and non-experts alike) say the opposite of each other on this topic and looking online is the same.

MoneySavingExpert.com has a forum posting with different opinions. Particularly strong opinions include Cardew's, which is:

looked at from every possible angle it is cheaper to have it on a timer; no question, there should be no debate(but there always is)

This question has been asked on this forum time and again.

Look at the Energy Saving Trust and they are categoric - a timer is cheaper!

although the Energy Saving Trust doesn't actually stipulate either way as far as I can find, although it discusses setting your timer based on warm-up and cool-down times.

TheGreenAge.co.uk says it depends on the age of your house and whether it has good insulation or not.

I am sceptical that using a timer will save energy because I see it that the fabric of the building gets cold then you have to warm it up again before the house gets warm, and as Conor says on the MoneySavingExpert.com forum:

Basic laws of physics state that it takes far more energy to heat to warm from cold than it does to heat from warm to slightly warmer. In addition to that, heat rises so for quite a while when the heating comes on, most of the energy is spent heating the volume of air above head height so it takes longer for you to feel any benefit. Don't believe me? When the thermostat clicks off as it gets to temperature, measure the air temperature at the height of the thermostat then measure it at ceiling height. You'll find a noticable difference. Just think of how much time the heating has been running and heating the ceiling as it brings the air temp at lower heights up to the set level every time the timer is set to come back on. With "always on", that period doesn't exist. The only time there's benefits with using the timer is if there are really long periods where the house is unoccupied and heating not required, say a single period of 8-10 hours a day. (that's 8-10 off, not how long you're out the house)

Who is right?

Laurel
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Chris Rogers
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  • What exactly do you mean running 24 hours? – Joe W Jan 28 '19 at 14:21
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    @JoeW - running 24 hours is leaving central heating on all day and all night just leaving room thermostat to control heating to maintain constant temperature – Chris Rogers Jan 28 '19 at 14:48
  • After reading the posts I think it is missing a few key points/questions. First what is the outside and inside temperature? Trying to maintain a house at a warmer temperature rather than wearing warmer clothing? I would say that there is difference in how it works if talking about Northern Canada versus Florida. Also I would think it's more important to look at how long it is running each day overall as that is what really matters. – Joe W Jan 28 '19 at 15:10
  • @DavePhD - This has nothing to do with setback thermostats. This is to do with using timers to switch the hearing off for pre-determined periods of time during the day – Chris Rogers Jan 28 '19 at 17:30
  • Second scenario seems to be putting forward the idea that it's not the entire purpose of timer thermostats to leave the heat off for extended periods of time, then turn it on shortly before the occupant comes back home (or gets up in the morning). – PoloHoleSet Jan 28 '19 at 17:52
  • I'm confused @PoloHoleSet. There are no scenarios given other than "Is it cheaper to use a timer or leave the heating on all day and night – Chris Rogers Jan 28 '19 at 18:21
  • "*The only time there's benefits with using the timer* is if there are really long periods where the house is unoccupied and heating not required, say a single period of 8-10 hours a day." - the second scenario acts as if this is not a primary use for a timer. My comment is more about how the person making that argument is setting up assumptions favorable to what they want, not a criticism of your question, as asked. – PoloHoleSet Jan 28 '19 at 19:14
  • I agree with @DavePhD -- Think of turning the heater off as equivalent to setting the setback temperature as low as possible. It's a duplicate. – David Hammen Jan 28 '19 at 21:42
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    I realize theoretical answers are off topic here but the amount of energy to heat a house is (roughly) proportional to the amount of heat the house releases to the environment, and clearly the latter is lower if the temperature is allowed to dip temporarily. – Reinstate Monica Jan 28 '19 at 21:53
  • @DavidHammen - I am having trouble agreeing with you and DavePhD at the moment as the setup of the CMHC study in the prospective dupe is unclear and the pdf is inaccessible. I think it is only fair to see if the original post is edited or a clear answer is provided here. – Chris Rogers Jan 28 '19 at 23:20
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    Someone doesn't have foggiest idea as to the basic concepts of thermodynamics. The only argument would be about how significant the savings are -- in many cases, with a well-insulated home, the savings of using some sort of setback would be trivial. (And, yes, there are a few cases, with oddly-designed heating systems, where setback could cost more.) But, in general, heat loss is proportional to delta T. – Daniel R Hicks Jan 28 '19 at 23:57
  • Can you not explain it in plain and simple to understand terms @DanielRHicks instead of terms such as *"heat loss is proportional to delta T"*? What's delta T and how is that determined? Not everyone understands physics and thermodynamics, hence the reason why the question receives conflicting answers. At least then **we** will have a definitive answer everyone understands – Chris Rogers Jan 29 '19 at 00:08
  • @ChrisRogers I can't open the other answer's link either. However, there is quantitative data here: https://www.healthyheating.com/downloads/Thermostats/nrcc48361.pdf and here https://nrc-publications.canada.ca/eng/view/fulltext/?id=344f31a2-8d67-4c5a-84bd-488fe7a18f59 – DavePhD Jan 29 '19 at 00:39
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    @ChrisRogers - [Newton's law of cooling](https://en.wikipedia.org/wiki/Newton%27s_law_of_cooling). Delta T is the temperature difference between two objects, in this case, the temperature difference between a house and the outdoors. – David Hammen Jan 29 '19 at 01:07
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    @ChrisRogers - I answered you, but, not too surprisingly, my answer was quickly deleted by the mods. Find yourself a basic book about thermodynamics and heat transfer and study it. – Daniel R Hicks Jan 29 '19 at 02:08

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