Walter Cohen wrote:
Hello.
I live in NY.

I am wondering if it is better to leave a central a/c unit running
during the day when no one is home, either at the normal temperature
or at a few degrees warmer -or- use a set-back thermometer when
leaving for work in the morning and have the A/C unit start up again
an hour or 2 before coming home later in the afternoon?

I use a set-back thermometer and it takes my unit 3 hours of
continuous operation to bring the temperature down 8 degrees.

Some people have told me that it makes more sense, energy wise and
cost wise, to not set the thermostat warmer in the morning and have
the unit struggle for hours on end in the afternoon trying to get
back to the original comfortable temperature. Instead they say to
leave the A/C on as it would probably cost the same if not less to
periodically cool an already cool house instead of cooling a house
that is not cool at all. Con Edison says to turn off the A/C when no one
is home but I think
they refer to window units (as they also say to turn the AC back on
again via auto-timer a half hour before returning - a half hour would
do nothing for me)

Thoughts?

Thanks,
Walter

I fear your installation is one that is not easy to say. I would guess
that there will not be a great deal of difference in the results either way,
some days you may win and some days you may loose. If it were me, I would
(and do) use a setback thermostat. Even setting it back a few degrees will
help Turning it off or allowing too much of a setback could cause it to run
for a long time during the hottest part of the day when it is less efficient
wiping out all or some of the savings of setting it back.

--
Joseph Meehan

Dia duit