Not correct. Heat flow is proportional to some power > 1 of the
temperature difference. It's been too many years since I knew and I'm
too lazy to look it up tonight. But reducing the temp diff by 1/4 will
save a lot more than 1/4 of the energy use and thus of the bill.
Harry is mostly correct on this one. The rate of heat loss from a
closed system is proportional to the temperature difference. Cut the
differential in half and you cut the heat loss rate in half. If you
have a sealed tank with water at 70, it will take twice as much heat
input to keep it at 110 as it would to keep it at 90. However, a
house isn't closed. Not only do you lose heat through the walls,
ceiling, etc. you also lose some heat due to air leakage. But
overall, I'd say Harry;s estimate is in the ballpark.
On Wed, 20 Oct 2010 11:36:53 -0700 (PDT), firstname.lastname@example.org wrote:
Sorry, yes, you're right -- for conduction.
For radiation, the transfer rate is proportional to the difference
between the fourth powers of the temperatures:
So with good insulation in the case under discussion, with most of the
heat interchange being conductive, the total interchange is close to
However, most wall systems do involve some radiative transfer too, and
walls with no insulation will have quite significant radiative
transfer. However, I don't know just how much.
Old houses often have little or no insulation in the walls.
My place is double brick, with 3/4" batten strips , covered with wood lath
and horse hair plaster. I would have to tear off the plaster and window
trim to add the framing and insulation.
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