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On Oct 29, 8:22 pm, "Ed Huntress" wrote:

I've seen those studies for years, Don, starting with a book I read in the
'70s, titled something like _Low-cost, Energy-efficient Shelter_. What the
DOE says is widely known.

--
Ed Huntress

What the DOE says is widely known, but incorrect. Don has explained
the problem correctly. Thermal mass and insulation determine the
thermal time constant, which affects how much saving results. But
has no effect on whether there is a savings.

As Pete C. points out there are some heating systems that change
efficiency depending on the demand. Heat pumps are one case. Another
case is modulating furnaces. These will be less efficient at higher
loads. But the common furnace located in a non heated area, will be
somewhat more efficient as the furnace will run for a longer time
before shutting off and loosing heat to the unheated area.

Dan

Hot water reset systems also operate at higher efficiency if the demand is
lower, since the water temperature is reduced, resulting in a greater delta
t in the boiler and more efficient heat transfer. With the right insulation
and very limited air changes a steady state high efficiency heating plant
without a setback might be more efficient. But very few residential systems
operate like that.