"Jeffrey J. Kosowsky" wrote in message
...

We are about to install several new circuits as we upgrade the
electrical systems in this very old house.

Any difference in price between #12 an #14 wire should be minimal; e.g.. a
few cents per foot. Breakers prob. identical price.
Also; if you have a situation where you may need more capacity than a 20 amp
circuit can handle, this might typically be a kitchen area, a suggestion.
Instead of two wire (White?Black plus ground) #12 install three wire
(White/Black/Red plus ground) #12. This will allow all the outlets on that
run or perhaps just one or two important ones to be 'split'. That is each
outlet can be wired so that the upper half of a duplex connected to one leg
of the supply and the lower half to the other leg of the supply thus
doubling the capacity of the circuit. The additional cost of the third
conductor will be small. The only other cost will be that of a two-pole
breaker in place of a single pole breaker.