Update: The Lennox dealer mailed us a written bid to add the furnace. The total to add the furnace is $4382 indlucidng a $230 multi-system discount. It's a G71P60C-110 with 110,000 BTU and 95% efficiency, two-stage, variable speed fan. The Lennox A/C is XC15-042 3.5 ton up to 14 seer unit. I agree about getting a third quote, though the Lennox dealer installed a new furnace in our previous old (1908) home and we are pleased with the quality of work they do. I'm not sure I understand what a manual J load calculation is. I know the Lennox salesman used his calculator quite a bit before he wrote the bid. The American Standard salesman did also; and they both came up with the same 3.5 ton, 14 seer number. Gary, I'm not sure why you think we won't use the A/C much here. Our upstairs is swealtering at night in the summer, after the sun has blasted our entire west side. The temperature in our bedroom is often 80 degrees or so when we go to bed. The summers have been quite hot for the past five to seven years. The season may not be as long as Phoenix, for example, but it gets pretty hot.

tigerdunes -- thanks for your input! Much appreciated. That is the direction I'm heading, subject to final price, warranties, etc. (The last quote from Company 2 had the Infinity furnace with the Comfort A/C.) The tendency here seems to be the "1 ton / 500 sf" approach. I've been pushing the final two dealers to really be sure about their sizing by giving them as much info as possible (the number of windows in the house, no insulation, orientation, etc, etc.) vyasmk9 -- I'm on the Peninsula -- as are all of the contractors I've contacted. It just seems that people around here seem to service a smaller area (although I could be wrong), plus I like to support local biz whenever I can. Just FYI, I started by selecting a couple of well-known brand names (Trane and Carrier) and looking on their websites for local dealers. Followed that up with searches for reviews of those dealers on local.yahoo.com and yelp, as well as checks on the BBB. Also asked my electrician and utility company guy for their thoughts/referrals. Not sure what the forum rules are for recommending contractors, so I'd rather ask before naming names. Anyone want to comment?

Amana is same as goodman. I'm not a fan of their A/C's - heatpumps but I"m ok with their furnaces. The do have a good warranty and some people like them. Its a matter of opinion. PRicing isn't amazing but not terrible either. For that same money you could probably get a dual fuel system (highefficiency gas and heatpump) for the same price. Their is other less expensive brands. I would ask for another brand personally.

Mike_home, thank you so much for helping. I agree that most of San Diego County has near ideal weather most of the year. We live 5.7 miles from the ocean, so we're not arid, but not humid most of the time. We've been having some really funky weather what with climate change and all. We have had heat waves into the 90s with onshore flow that were relatively dry and comfortable, but we've also had upper 80s with 80-90% humidity for 1-2 weeks at a time, which is pretty bad but really rare, maybe 2-4 weeks a year. To your questions: the house was built in 2005 and has 5368 total conditioned square feet. Here are the units we currently have: 3.5 ton - upstairs less master (2040 SF, 10 to 13.5 ft ceilings) 2 ton - master suite 606 SF (10' avg ceilings) 4 ton - lower floor (2722 SF, 10' ceilings) The house is 9 years old, current condensers are approximately 3-4 years old, furnaces and coils 10 years old. I have not thought to repair the equipment because it's "working" - you know, turning on, providing cool air, etc., just assumed it was because they were cheap SEER 10 units and therefore not working well, but I suppose it's the BTUs and not the SEER that determine cooling capacity. I'm not convinced four 8 x 14 registers (plus a few small ones for the bedroom and baths) are enough for the 2040 SF main upstairs area (of which 617 sq ft has 13.5 to 18 ft ceilings plus cool air loss down the stairs, I estimate a volume of about 30K cu ft. We also have 4 large windows, a 10 x 16' skylight, and 10' x 22' sliding glass doors. All glass is dual pane and tinted except our new 11 x 5' kitchen window. I believe we need more registers here. The master suite has another issue: in addition to the vents and return in the suite, the master unit feeds an 8 x 14 register to the living room, such that when just using the master unit, unconditioned air blows in from the living room under and around the door, drastically reducing the conditioning effect in the master suite. I strongly believe we need to disconnect the duct leading to the living room and restrict the master system to the master suite. The downstairs remains cool most of the summer and rarely needs A/C, but I suspect humidity may become an issue at times when we're in the 60s and near the dew point. I don't know if a dehumidifier wouldn't be the most cost effective solution rather than replacing the A/C compressor and furnace. I am also in the process of looking into sealing and insulation. They tore the insulation out of the attic to remove walls and install a new flat ceiling on the 2nd floor, and I'm pretty sure the insulation was not reinstalled properly, because even on 80-85 degree days it gets hotter than the outside. Downstairs stays almost 10 degrees cooler and almost never needs A/C use. The garage has never had insulation above it; completely virgin attic space, though the garage is not conditioned space. I believe good attic insulation would significantly reduce our cooling needs upstairs. Thanks again to all those who look and help out! David