Reply #24: You explained it correctly, but that quote may lead some people astray.

[Tesha]

  ____________                  ________
              \                /
Temperature    \              /
             |  \____________/  |
             |                  |
       day   |vv|   night    |^^|  day


          _ _ _               ___
   (100%)                    |   |
  ___________                |   |______
             |   $$$$$$$$$$$$|
Heat         |   $$$$$$$$$$$$|
Demand       |   $$$$$$$$$$$$|
             |   |
   (0%)_ _ _ |___| _ _ _

> "The fuel required to reheat a building to a comfortable
> temperature is roughly equal to the fuel saved as the
> building drops to the lower temperature."

You explained it correctly, but that quote may lead
some people astray so I'm going to try and reinforce
what you said.

We can divide "the heating day" into four periods:

1. The daytime when the temperature is steadily warm (say, 68°).
2. The evening cool-down period ("vv")
3. The nighttime period when the temperature is steadily cool (say, 60°)
4. The morning warm-up period ("^^")
(5. The next day's daytime period)

What the quote is trying to explain is the idea that while
the heat does run heavily during the morning warm-up period,
that extra heating is balanced just about exactly by the
fact that the heat probably doesn't run *AT ALL* during
the evening cool-down period. After all, you're letting
the house cool from 68° to 60° and you don't run the heat
to cool things off.

Meanwhile, the whole nighttime cool period is gravy ($ savings).
It costs you less heat to keep the house at 60° than it does
to keep it at 68°. It always makes sense to run the thermostat
at the lowest temperature you can stand, keeping in mind the
risk of frozen pipes if you let the house's interior temperature
drop too low.

Tesha