In the market for a new heating/ac system. Had 2 sales guys come out to quote and each had a different opinion on what could be an effective solution for us. Another 2 coming later today.

Here's our quick situation: 3000 sq ft single level home, L-shape flr plan w/ living space on 1 side of 'L' and BR's on other. BR's further away from furnace - MBR furthest - and getting very little heat. Ducts have been checked - no major leaks, combo of 12" (core runs) and 6" (fingers). Current unit is York - 17yrs old and described by all as 'junk'. We live in SF Bay Area hills (CA)- winter temps down to upper-20's, summer highs to upper 90's.

1st guy: admitted his top rec was the best and most expensive, but suggested Carrier Infinity (58MVP120 + 38TDB060 + new coil + 2nd return) with 2-zones, 1 for living, 1 for sleeping areas. made sense given that we spend days in living space and night in BR's. but fairly expensive ($13k all-in, incl discounts).

2nd guy: said 2 zone was a waste for single level and we could do just fine w/ single zone. he suggested trane xb-90 120,000btu + adding dedicated single run to MBR + add'l return + new a/c coil. a/c condenser still running, so keep it, but change coil to avoid re-installing furnace when coil goes. his price quote $7k.

heard that zoning runs ~ $2.5k and a/c condenser $4k, so quotes seem comparable adjusting for add'l stuff. Tho Carrier unit is the more advanced 2-stage vs. trane unit - don't know how much $$'s that counts for.

can anyone answer the 1 vs. 2 zone question for us? most threads on 2-zone have related to 2 story home and ours is single level. in reading threads i learned to appreciate that installation is more important than brand name, but would welcome sizing/efficiency recommendations from anyone.