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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?

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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
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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
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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
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    @ChrisRogers - Newton's 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 1:07
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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 2:08

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