Here is the main problem: I do not have enough information to give
you an answer. Here is why:
The balance point is always determined by:
Heat/Load Calculation of House
Outdoor Design Temp.
BTU output of equipment.
These should be determined prior to install by contractor (ask for the
Manual J, mandatory in some states), and unfortunately, your
installers are not usually given this information (nor is it my
experience that they are trained in this area).
RULE OF THUMB: Set it as low as possible, if not comfortable, then
move it up. Try setting at 35, if you can go lower..go lower. If you
can go higher...go higher. Your Heat Loss Calculation in conjunction
with those mentioned above determine everything but bottom line, it is
about your families comfort. But keep in mind that a heat pump is
less efficient at lower temps. Oil in my area cost $3.30/gal,
electricity is $.25/kw which makes the electricity a bargin. This is
also part of your calculation I cannot determine for you.