Fuccillo111 ' s scenario illustrates an interesting phenomenon...
let's assume for a minute the actual outdoor temperatures for each test period WERE identical...
as well as wind.. available daytime sunlight etc
.. let's also assume his hopper measurements were also accurate.. And exactly 1 20 pounds
... it's obvious with his numbers that he actually used the same amount of coal keeping his house COOLER with set back temperatures then he did keeping his house WARM ( maintaining a constant 72 degrees)... but heres why this would not be an accurate comparison
outdoor temperatures and weather vary a lot hour by hour... even when we feel it is consistent
prevailing wind speed and direction... duration... at different times of the day (or night)..available sunlight (cloudy-clear) ..humidity and pressure cumulatively play a role on the cooling ( or heating) of a house. Not to mention.. a consistent 72 degrees is actually warmer than his 3 setback temps (an average of 70)
... the bottom line is over a long timeperiod.. set back temperatures will conserve fuel.. regardless of the type of fuel . Coal has the ability to maintain a longer holdover temperature... so in the end it boils down to comfort. and whether the savings are actually worth it.. large step back temperatures on a regular basis(daily) are somewhat inefficient... especially if the appliance(coal fired) has slow recovery... if you set back temperatures at all keep them within 3 to 6 % (percent) of your anticipated or desired temperature.. setbacks using coal fired appliances will save fuel... but because it is such a inexpensive fuel... it will take time to experience the savings