wrote:

On a typical winter day for those living in cold climates, how much
water (condensation) is produced by a high-efficiency furnace per day?

You might figure about 5% of the fuel's heating value for oil, ie
0.05x140KBtu/1000 = 7 pounds per gallon, eg 42 lb/day of water, if
you burn 6 gal/day of oil, and about twice that for natural gas.

And would this amount to more or less than what is produced by a
central air conditioner?

Depends on the humidity and house air leakage rate. If wi = 0.00787
(80 F at 50% RH) inside and wa = 0.0130 (Phila in July) and a 2400 ft^2
house leaks 224 cfm (a 0.7 ACH average), the AC needs to remove at least
24hx60x224x0.075(wa-wi) = 124 pounds of water per day.

Nick