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    • MSE Guy
    • By MSE Guy 4th Dec 12, 6:43 PM
    • 1,628Posts
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    MSE Guy
    Energy myth-busting: Is it cheaper to have heating on all day?
    • #1
    • 4th Dec 12, 6:43 PM
    Energy myth-busting: Is it cheaper to have heating on all day? 4th Dec 12 at 6:43 PM
    This is the discussion for the following MSE guide.


    Energy myth-busting: Is it cheaper to have heating on all day?
Page 43
    • richardc1983
    • By richardc1983 31st Oct 16, 10:17 PM
    • 1,889 Posts
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    richardc1983
    The cooler the return flow the better condensing - so get it as cool as you can. There isn't just condensing mode or not at all there's further efficiency the lower you run it.
    If you found my post helpful, please remember to press the THANKS button! --->
    • malc_b
    • By malc_b 1st Nov 16, 9:33 AM
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    malc_b
    That is a rather strange scenario that re-enforces the doubts in your assumptions. Who would be daft enough to drive around for 30 minutes if they arrived early at a destination ? Most people would park up and just wait. The above statement does not do much for the credibility of your "proof".
    Originally posted by ASavvyBuyer
    It's a metaphore, but as you ask I would say someone dropping the wife and kids off in central london for a premier. No parking anywhere close and what parking there is is loadsofmoney. Cheaper to circle for 30 minutes than pay for parking. But it's not the point. It using something else that have varying efficiency to explain CH.


    Your assumption in the calculation is that the boiler will not run in condensing mode if it is switched back on after being off for a period of time. However, the return temperature of the water will be well below 50 degrees when it is switched back on, and with proper controls, will stay below 50 degrees. Therefore, it will be running in condensing mode whenever it is running, providing the user has not used the controls to set it at too high a temperature.
    Originally posted by ASavvyBuyer
    My point is that a house over 24hrs loses a certain amount of energy. If you turn off the heating over night or more often then this doesn't affect the total 24hr loss by that much. I've done the maths and for a fall to 10C I've come up with ~8%. I've seen figures of 5% and the 8% would be 4% with better insulation.

    Can we agree on this?

    You might be able probably google this. I have notes from "16293: Environmental Engineering Science 1" which gives factors of 1.0 for 24hrs, 0.85-0.95 for heavy building with night time shutdown, but note this is for a factory with an 8hr working day. Houses have a shorter night which is why I worked it out myself from basic physics.

    Once you accept that it doesn't make much difference 24 vs 16/8 then you realise that the energy must come from somewhere. It must come from the boiler and radiators. Hence they must be working harder and the radiators must be hotter.

    Some other points that have been raises elsewhere:

    1. Yes running at lower return temperatures improves efficiency however there is step change going from non condensing to condensing mode followed by a slow increase. We need to be in condensing mode. If we can also run cooler than that as well then good but the gain going cooler is smaller so might not offset the cost of running longer.

    2. "My system already run in condensing mode all the time as I force the return water to be below 57C". Good. This is exactly what I have said. Run in condensing mode for as short a time as you can. My only point is that if that doesn't work out for you then running longer hours is likely to be cheaper than not running in condensing mode. That's what the maths show.

    3. "The saving due to running in condensation mode is small compared to the saving by turning the heating off". No. This is exactly what the maths show. The overnight saving is small and comparable with the saving for running in condensing mode.

    4. "Your assumptions don't match the real world." Unless you live in a 1 room house where the outside temperature is a fixed 0C then you are correct. It's not meant to be a specific house it's meant to explain the process so that we have better understanding of how it works.

    5. "You have simplified the maths too much". I have covered this. Feel free to do more accurate calculations but I found it made around 10% error (that is 10% of the 8%) which I mention in the proof. My approach btw was to use a spreadsheet to do a minute by minute calculation. Once you have worked out one equation to give the new temperature then you can just drag it down to generate the temperature points for the entire night.

    6. "I don't need to run 24hr, my system just starts a bit earlier". I didn't say you did. I did the proof to square the circle as some people were posting that they saved money running 24hr. Rather than dismiss them as idiots I decided to see if there was any possibility they were correct. I found that there are conditions where they could be correct, but, rather than being either 24hr or at little as possible, the heating has a sweet spot for lowest cost.
    • gazza007
    • By gazza007 3rd Nov 16, 3:30 PM
    • 245 Posts
    • 44 Thanks
    gazza007
    Smart heating
    I am on the current EDF energy club switch so cheapest fuel but after a lot of research I installed the Tado smart system Sept 15. One of the best purchases I have ever made. It is so fire and forget. It looks after itself, very clever and well engineered like most German things. One thing that most people forget even without a smart thermostat and geofencing app is getting a Balance across your radiators, using TRV's where possible and ensuring that the temp thermostat doesn't cut out before the other rooms reach their required levels.
    • lstar337
    • By lstar337 4th Nov 16, 11:08 AM
    • 3,270 Posts
    • 1,762 Thanks
    lstar337
    I have grown bored of stating the same points over and over, but hopefully those with a basic grasp of physics will read the majority of posts and save money by not pointlessly running their heating 24/7.

    Those who wish to waste money are free to.

    Malc, sorry but you still haven't provided any proof (not based on assumptions that in my opinion need not apply), so I'm unconvinced.

    Those who want to save money, if you have a condensing boiler then turn down the output as much as your house allows, and heat for as short a period as possible. Don't heat for 24/7 if you don't need to, and don't heat while you are out of the property.
    • orrery
    • By orrery 4th Nov 16, 2:16 PM
    • 529 Posts
    • 446 Thanks
    orrery
    My boiler won't run at high power. The output is set at 55c so the return is always less...
    Originally posted by lstar337
    For many people who use the same boiler to heat a h/w tank, the output needs to be 60C or more to ensure that bacteria can't develop.

    Also, setting such a low temperature will cause my own Vaillant boiler to frequently shut down during the ignition sequence, as it will be unable to perform it's ignition test sequence (always starting on full power) before going over temperature.
    4kWp, Panels: 16 Hyundai HIS250MG, Inverter: SMA Sunny Boy 4000TL, SolarImmersion
    Location: Bedford, Roof: South East facing, 20 degree pitch
    Nissan Leaf, TADO Central Heating control
    • lstar337
    • By lstar337 4th Nov 16, 4:22 PM
    • 3,270 Posts
    • 1,762 Thanks
    lstar337
    For many people who use the same boiler to heat a h/w tank, the output needs to be 60C or more to ensure that bacteria can't develop.

    Also, setting such a low temperature will cause my own Vaillant boiler to frequently shut down during the ignition sequence, as it will be unable to perform it's ignition test sequence (always starting on full power) before going over temperature.
    Originally posted by orrery
    Well I was simply talking about my own setup at that point. Obviously if individuals have less equipped/capable boilers and/or setups then they would need to account for that.

    As I said in my last post:
    Those who want to save money, if you have a condensing boiler then turn down the output as much as your house allows, and heat for as short a period as possible. Don't heat for 24/7 if you don't need to, and don't heat while you are out of the property.
    Originally posted by lstar337
    So go as far as you can get away with basically.
    • magicsnaps
    • By magicsnaps 1st Dec 16, 11:28 AM
    • 13 Posts
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    magicsnaps
    A question. We're lucky enough to have underfloor heating on the ground floor, but cannot agree between us how to run the system. On all the time, controlled by thermostat or switched on and off by timer for set periods? Please save the relationship.
    • richardc1983
    • By richardc1983 1st Dec 16, 12:53 PM
    • 1,889 Posts
    • 1,006 Thanks
    richardc1983
    Underfloor heating is better to be left on all the time with night set back due to the long response times. Set your thermostat to say 20C when occupied and 18C when non occupied eg in bed or out at work.
    If you found my post helpful, please remember to press the THANKS button! --->
    • orrery
    • By orrery 1st Dec 16, 3:24 PM
    • 529 Posts
    • 446 Thanks
    orrery
    A question. We're lucky enough to have underfloor heating on the ground floor, but cannot agree between us how to run the system.
    Originally posted by magicsnaps
    If it is electric, then is it on economy 7? That would mitigate in favour of it being on for the E7 period.

    It should always be on a thermostat - that just prevents the heating being left on when the room is hot enough.

    With any appliance, I'd always try to keep it on for the minimum period required to do the job. If you want it on when you get up in the morning, set it to come on for a period before you need it, then try increasing and decreasing that period until you find the shortest period that works. Then try the same experiment turning it off before you need it off - the floor will store a lot of heat.

    The general rule is - the longer you keep heating turned on, the more time there is for that heat to leak out and the more it costs you.
    4kWp, Panels: 16 Hyundai HIS250MG, Inverter: SMA Sunny Boy 4000TL, SolarImmersion
    Location: Bedford, Roof: South East facing, 20 degree pitch
    Nissan Leaf, TADO Central Heating control
    • daveyjp
    • By daveyjp 1st Dec 16, 6:32 PM
    • 7,201 Posts
    • 5,604 Thanks
    daveyjp
    My parents have hot water underfloor heating throughout their bungalow. Every room is seperately controlled so thermostats are set for comfort in each room.

    Even at this time of year once the concrete is warmed through the heat soon builds to well above the stat temp so the boiler is hardly firing.
    • Cardew
    • By Cardew 2nd Dec 16, 9:30 AM
    • 27,114 Posts
    • 13,226 Thanks
    Cardew
    A question. We're lucky enough to have underfloor heating on the ground floor, but cannot agree between us how to run the system. On all the time, controlled by thermostat or switched on and off by timer for set periods? Please save the relationship.
    Originally posted by magicsnaps
    You haven't stated whether it is electric UFH or by hot water through pipes.

    As stated above, the principle of UFH is to have the heating medium at much lower temperature than conventional radiators. This entails having the heating on for longer periods.

    Like any form of heating, heating is a compromise between comfort and cost. The longer heating is off - the cheaper to operate. Nobody can state what is best for your conditions; you need to experiment to get the acceptable level of warmth.
    • zebb
    • By zebb 21st Mar 17, 7:44 PM
    • 12 Posts
    • 9 Thanks
    zebb
    I haven't been back to this thread for over 4 years but thought the following might be helpful. Apologies if this has been posted previously but forgive me for not checking thru 43 pages of posts!

    Prior to 2013, in an attempt to save wasting heat, and on those occasions when I could be bothered to do so, I turned down the TRVs in our lounge when I went to bed and turned them up again in the evening - as we just didn't use our lounge during the day. Then I discovered programmable TRVs and now use them not only in the lounge (no longer have to remember to adjust them!) but also to control the heat in some other areas - particularly the bedrooms. Its lovely and warm when we wake up and go to bed but the bedroom is set lower during the day and early evening. It didn't cost a bomb, I used the Pegler Terrier i-temp. Bought 4 of them from Hamilton Gas products on their buy 3 get one free deal. All for just £75. (I see they're still doing the same deal now too!).

    The bottom line is that my average winter oil usage has changed as follows:

    6 Years to 2013 : 1950 Litres
    4 Years since 2013 : 1700 Litres

    I don't claim it to be scientific. It doesn't take into consideration how cold the different winters were. But, its a fact that my oil usage is averaging nearly 13% less - AND I'm more generous to MOH in that I now actually encourage her to turn the temperature up higher whenever she needs it!! And its still cheaper than before. Lovely gubbly!
    • victor2
    • By victor2 22nd Mar 17, 8:03 AM
    • 4,723 Posts
    • 3,145 Thanks
    victor2
    I haven't been back to this thread for over 4 years but thought the following might be helpful. Apologies if this has been posted previously but forgive me for not checking thru 43 pages of posts!

    Prior to 2013, in an attempt to save wasting heat, and on those occasions when I could be bothered to do so, I turned down the TRVs in our lounge when I went to bed and turned them up again in the evening - as we just didn't use our lounge during the day. Then I discovered programmable TRVs and now use them not only in the lounge (no longer have to remember to adjust them!) but also to control the heat in some other areas - particularly the bedrooms. Its lovely and warm when we wake up and go to bed but the bedroom is set lower during the day and early evening. It didn't cost a bomb, I used the Pegler Terrier i-temp. Bought 4 of them from Hamilton Gas products on their buy 3 get one free deal. All for just £75. (I see they're still doing the same deal now too!).

    The bottom line is that my average winter oil usage has changed as follows:

    6 Years to 2013 : 1950 Litres
    4 Years since 2013 : 1700 Litres

    I don't claim it to be scientific. It doesn't take into consideration how cold the different winters were. But, its a fact that my oil usage is averaging nearly 13% less - AND I'm more generous to MOH in that I now actually encourage her to turn the temperature up higher whenever she needs it!! And its still cheaper than before. Lovely gubbly!
    Originally posted by zebb
    Nice way to balance usage and comfort though...
    • malc_b
    • By malc_b 22nd Mar 17, 8:12 AM
    • 977 Posts
    • 378 Thanks
    malc_b
    What you want to do is to find the degree days history for your location and use that to adjust your annual usage figures to compensate for the weather effect. That way you'll get a better idea of the savings due to your changes and the savings due to the warmer winters.
    • uk1
    • By uk1 22nd Mar 17, 10:50 AM
    • 996 Posts
    • 647 Thanks
    uk1
    Zebb, no doubt at all about your finding but I'm just interested ...... how do you know with any degree of accuracy how much oil you've been using?

    I'm able to guage very roughly what is in the tank even though we have a digital scale and I know how much we buy but I have no idea how to work out consumption with any degree of accuracy.

    I just topped up with 1000 gallons and my Apollo guage shows me it's only a delivery of 880 .....
    • Cardew
    • By Cardew 22nd Mar 17, 11:47 AM
    • 27,114 Posts
    • 13,226 Thanks
    Cardew
    I haven't been back to this thread for over 4 years but thought the following might be helpful. Apologies if this has been posted previously but forgive me for not checking thru 43 pages of posts!

    Prior to 2013, in an attempt to save wasting heat, and on those occasions when I could be bothered to do so, I turned down the TRVs in our lounge when I went to bed and turned them up again in the evening - as we just didn't use our lounge during the day. Then I discovered programmable TRVs and now use them not only in the lounge (no longer have to remember to adjust them!) but also to control the heat in some other areas - particularly the bedrooms. Its lovely and warm when we wake up and go to bed but the bedroom is set lower during the day and early evening. It didn't cost a bomb, I used the Pegler Terrier i-temp. Bought 4 of them from Hamilton Gas products on their buy 3 get one free deal. All for just £75. (I see they're still doing the same deal now too!).

    The bottom line is that my average winter oil usage has changed as follows:

    6 Years to 2013 : 1950 Litres
    4 Years since 2013 : 1700 Litres

    I don't claim it to be scientific. It doesn't take into consideration how cold the different winters were. But, its a fact that my oil usage is averaging nearly 13% less - AND I'm more generous to MOH in that I now actually encourage her to turn the temperature up higher whenever she needs it!! And its still cheaper than before. Lovely gubbly!
    Originally posted by zebb
    Whilst the savings are impressive, the post isn't addressing the 'myth' which is the title of this thread.

    Your programmable TRVs are simply turning off/down the radiators in the rooms not in use; something many of us do manually.
    • zebb
    • By zebb 23rd Mar 17, 10:52 PM
    • 12 Posts
    • 9 Thanks
    zebb
    Thanks for your comments folks. I did write a response but something went horribly wrong as I went to submit it. So, I’ll try again:

    Malc: Yes, thanks, may well do that.

    UK1: I have a Titan 3600 litre round tank which is effectively in 4 sections progressively decreasing in diameter from bottom to top. I use a simple dip stick – divided into 100 units – and measure the tank once a week. By some simple maths, I’ve estimated the proportionate volume in each section – for example bottom section holds 40 litres per unit and the top 32 litres. Its proved pretty accurate over the years, being able to forecast a reading after a delivery to within 0.5 unit.

    Also, 4 years ago, I investigated installing a flow meter on the pipe but the costs seemed prohibitive. Instead, I had the idea of attaching an hour meter to the pump/burner unit . It cost just a tenner. The nozzle is .75 meaning it delivers .75 US gallons per hour which equates to .62 imperial gallons or 2.84 litres per hour. Since October, the hour meter has just clocked up 500 hours – implying its used 1420 litres. My dip stick measurements show I’ve used just under 1400 litres in that time. So, it seems the old method was reasonably accurate! I suppose I could stop the weekly reads but old habits die hard. Anyway, they confirm I haven’t had a leak or have had any oil stolen!!

    Trust this explains and may be of some help.

    Cardew: I appreciate my post wasn’t directly related to the thread and apologise if I should have posted it elsewhere. Just thought people may be interested in a cheap way of saving energy and which didn’t require manually turning the TRVs up and down everyday. As an aside, I’ve just had the HIVE system installed (so yes, it can be installed on oil burners) and a bi-product of this is that for each day you get half hourly temperature readings. Initially thought I might use this in conjunction with my hour meter readings to compare and test the myth. However, apart from the obvious difficulty of needing 2 identical days weather conditions, we also have the problem that our boiler has its own thermostat. Very rarely do we reach our target temperature in one burn ‘session’. Indeed, there are even occasions (in the morning) in very cold or windy weather when we don’t even reach our target (house) temperature at all. Another difficulty I foresee is that we notice that the house can seem warmer when it is warming up (presumably cos the boiler and radiators are permanently ‘on’) than when its finally reached the target temperature (when boiler is only intermittently on). In light of these ‘difficulties’, I think it unlikely we will attempt to test out the myth. Will instead concentrate on comfort and putting the heat where we need it most. So, once again my apologies, I think I now agree, I am on the wrong thread!!
    • d68
    • By d68 11th Oct 17, 10:04 AM
    • 1 Posts
    • 0 Thanks
    d68
    It's a bit more complicated. If the thermostat is "Calling for Heat" (i.e. the room temp is below the set temp) then the boiler will fire up and the pump will circulate heated water through the pipes. All radiators have a bypass (or if you turned one off, all the subsequent ones would go off also!), so even if the radiators are all OFF some heat is wasted in the floor / walls ('Wasted' if you don't need the heat which is presumably why the rads are turned off).
    A central thermostat has never made sense to me, as we have the bedrooms cool, the sitting room warm and the kitchen in-between, so each needs it's own stat, preferably linked to the thermostatic valves on the rads in that room. Works beautifully, but a bit expensive to buy.
    • Colmol
    • By Colmol 11th Oct 17, 11:34 AM
    • 1 Posts
    • 1 Thanks
    Colmol
    Regarding using tumble dryers mentioned in this thread, a lot of people don't know that it is possible to buy eco friendly GAS tumble dryers. These cost just pennies to run - about 5p per load at today's prices. I've had one since the mid 80s. There is only one manufacturer of gas tumble dryers in the UK and that is Crosslee. Cost is about £285 but you save buckets of cash over the years of use compared to electric tumble dryers. Just thought some might find this info useful.
    • Bricks
    • By Bricks 11th Oct 17, 11:55 AM
    • 56 Posts
    • 22 Thanks
    Bricks
    It's a bit more complicated. If the thermostat is "Calling for Heat" (i.e. the room temp is below the set temp) then the boiler will fire up and the pump will circulate heated water through the pipes. All radiators have a bypass (or if you turned one off, all the subsequent ones would go off also!), so even if the radiators are all OFF some heat is wasted in the floor / walls ('Wasted' if you don't need the heat which is presumably why the rads are turned off).
    A central thermostat has never made sense to me, as we have the bedrooms cool, the sitting room warm and the kitchen in-between, so each needs it's own stat, preferably linked to the thermostatic valves on the rads in that room. Works beautifully, but a bit expensive to buy.
    Originally posted by d68
    There are now various systems that allow you to "zone" a conventional heating system. Each radiator has a TRV but the TRVs can communicate with the boiler switch. Therefore each room can have its own timetable for when it calls for heat, and if only one room calls for heat, only the radiator in that room takes it, meaning heat isn't wasted in other locations. The system I use is the Honeywell Evohome one; it's not that cheap but hopefully worthwhile in the long time.
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