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PostPosted: Sun Nov 16, 2014 9:27 pm 
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whilst an excellent anallergy :thumbright:
you have no system losses [wasted energy] with it turned off
now you need to work out if the extra energy and time bring it back up to temperature is beneficial
but remember the hotter the temperature the greater the differential so the greater the heat loss
so the time its at a lower temperature it will be loosing less energy

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PostPosted: Sun Nov 16, 2014 11:33 pm 
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I wrote:
The only time you 'win' is when the temperature of the building falls to a level where it cannot go any lower - at that point you reach an equilibrium that doesn't require energy to match [the loses].


In my analogy the 'slightly open tap' at the bottom of the barrel represents the losses but, as I stated, when the house gets to its lowest temperature (ambient) the barrel is empty and all the flow IN goes straight OUT - THIS is when you're on the energy losing side and you are better off turning the system off. But ONLY if the barrel (house) gets to ambient. This is for the user to decide.

When the system is restarted (pouring the adjacent bucket back into the barrel) you - presumably - still have the fill tap running or you turn it back on so, despite the drain tap still being open the barrel refills to the brim and the ONLY losses are those via the drain tap i.e. there are NO losses of energy bringing it back to full temperature - it's all "in the barrel".

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PostPosted: Sun Nov 16, 2014 11:46 pm 
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One thing I should add.....

the analogy only works if there is a 'steady state' condition in place.

For example the energy losses/gains from the house heating as discussed are in a 'steady' condition only e.g if the conditions around&about the house remain the same.

If you switch the heating off on a still day then it starts blowing a gale, the house will lose it's heat QUICKER i.e. the losses increase and MORE energy will be required to reheat it due to those increased losses.

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PostPosted: Mon Nov 17, 2014 10:31 am 
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Your analogy of a barrel of water is actually very accurate however your interpretation of it is incorrect because you fail to take a factor into account as Big-all tried to point out as follows:
In your analogy water will drain from the barrel quicker when it is full or nearly full that when it is nearly empty. Think when its full from a hole in the side of the barrel near the bottom water will shoot out sideways but when the water level is only a little above the hole water will only trickle out. This means that maintaining the barrel at full will loose more water over time than a barrel that is say allowed to drop to half full then topped back up. The same is true of heating a house. It WILL take more energy to maintain it at say 19 deg than by allowing it to drop a few deg when the house is empty then heating it back up.

So energy is saved. How much energy is saved depends on how many deg the temperature drops by before the heating is turned back on and so ultimately how long the heating is off for.
In a well insulated house if the heating is off for say just an hour the temperature may only drop by 1/2 a degree and only a few pennies will be saved. If it is off for days, even weeks then you would save many pounds.

So the argument for turning it off is that it uses less energy and so saves you money and perhaps the planet? :dunno:

The argument against turning it off is firstly convenience. Do you want to come home from work early and have to manually turn the heating on then shiver for 1/2 an hour while the house heats up then remember to turn the heating control back to automatic so it will go off again tomorrow just to save a few pennies?
Second changing temperatures creates an environment that is more prone to damp than a steady temperature.

They say turning your heating up by 3 deg uses 2 x the amount of energy to heat a house.
Therefore I suspect that you'd save far more energy by turning your heating down just 1 deg and leaving it on all the time than by leaving it at its current temperature and having it turn off for a few hours occasionally.

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PostPosted: Mon Nov 17, 2014 12:36 pm 
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I have kept it on before, and really have not found my bill to go through the roof (no pun intended) I have found that it remains mostly consistent. Though it has been mentioned here before, the insulation that you have in your house is rather important and will determine a lot of the costs.


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PostPosted: Mon Nov 17, 2014 9:58 pm 
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Well i have to say insualtion is key to saving money as our bills have gone down due to needing the heating on as much. Now paying £90 per month for gas and electric compared to £120 before the insulating work was done.I still have more to do so even better savings to come. Not bad for a large house.


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PostPosted: Mon Nov 17, 2014 11:44 pm 
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mikew1972 wrote:
Your analogy of a barrel of water is actually very accurate however your interpretation of it is incorrect because you fail to take a factor into account as Big-all tried to point out as follows:
In your analogy water will drain from the barrel quicker when it is full or nearly full that when it is nearly empty. Think when its full from a hole in the side of the barrel near the bottom water will shoot out sideways but when the water level is only a little above the hole water will only trickle out. This means that maintaining the barrel at full will loose more water over time than a barrel that is say allowed to drop to half full then topped back up. The same is true of heating a house. It WILL take more energy to maintain it at say 19 deg than by allowing it to drop a few deg when the house is empty then heating it back up.

True - my barrel analogy really should ignore the effect of the weight of the water though.

For what you say is to happen then the heat loss from the house must have to vary with the temperature of the house and in my experience the temperature loss figure is a constant (steady-state condition as I inferred albeit latterly in the description), not a variable.

It will, of course 'vary' if the steady-state condition is not met i.e. a gale starts to blow.

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PostPosted: Thu Dec 25, 2014 4:31 pm 
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I'd only recommend keeping heating on 24/7 if you have a well insulated home with a weather compensation heating control system.

Heatloss calculations are based on the building maintaining a certain ambient internal temperatures.
While a building will maybe lose heat at a steady rate, the U value can vary for the same wall construction - depending on the orientation & exposure. So in effect a South facing wall will lose heat at a slower rate in daytime, than a North facing wall at night time. This can be significant, but like most things in heating design, common ground has to be found.

Then you have air infiltration, convector type emitters like radiator will result in more air infiltration & more room air changes - more heat loss! Whereas underfloor heating provides mainly radiant heat & limited air movement. The analigy here of radiant heat; a supermarket chiller aisle, the ambient temperature in the aisle is the same as other aisles in the supermarket but it feels cold, your body is losing more radiant heat to the chillers, hot always goes to cold......heat loss.

So in poorly insulated homes, heat it only when & if required.

Another point; standard On/Off bio metal room thermostats are calibrated to plus or minus 5*C, so if it's set at 22*C it could go off at 27 or on at 17. Hardly an exact science & hardly reliable enough to leave it on 24/7!!!

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PostPosted: Thu Feb 05, 2015 3:45 pm 
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I do not have good insulation so what I'm doing is to put the thermostat always on minimum 18°C so that my house do not get to 10°C in the winter. I think that when you go really low, the walls and the ground get very cold and to get it back it ask more energy...


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PostPosted: Wed Feb 18, 2015 1:46 am 
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I agree with that plus background heat can reduce condensation.


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