"Ignoramus10802" wrote in message
...
On 2009-10-29, Jon Elson wrote:
Ignoramus10802 wrote:
i
It's far more complicated than that. Factors such as insulation / heat
loss, type of heating, multi-stage heating, electric backup heat on
heat
pumps, etc. all come into play in determining the away duration and
temp
reduction where savings begin, and in some cases (typically high
efficiency homes) it can require a multi day absence to see any
savings.

This is patently untrue.
No, there is quite an element of truth! You have to compare the thermal
mass of the house and the heat loss. If the house had enormous thermal
mass, like lots of stone floors and massive stone fireplaces (some
people build houses intentionally to have very high thermal mass) then
although the furnace could warm the air quickly to make you comfortable,
it would still run for hours to warm up all that mass.

So what?

If you have a lot of thermal mass and low heat loss (good
insulation) then turning the thermostat down for a couple hors gives
no benefit. If you have low thermal mass and lots of heat loss,
then turning it down for even a couple hours will give significant
benefit.

Jon, with all respect, I must say that you are mistaken here.

From the law of conservation of energy,

heat input into the house == heat loss from the house

The lower is house temperature, the lower is the heat loss.

i

This is more equations than I care to handle, but a house with very good
insulation and high thermal mass is not going to benefit noticeably until
the temperature has dropped and stabilized. Otherwise, all you're doing is
cycling the cooling and warming of the thermal mass.

--
Ed Huntress