" U' N* k. Y% j0 b9 uoption 1: Two seperated furnances and seperated control ( @, d. g0 m8 H" s (for big house > 3000 ft)% A! d$ p* S) A9 k
option 2: One furnance with Zone Control device ( S) N7 x4 B5 `& q' y1 A2 t1 I7 R
(three zones or fours zone will be good) - total efficiency will be higher 9 z& `4 g# j% y: r# J2 o * o+ d0 S+ R+ a* I4 \! p% `Total cost is not big difference.