mims "I too am interested in learning more about negatives for a 2 stage condenser. Tigerdunes --- do you think the limited benefit is not worth the extra cost?" Correct. Now having said that, these manufacturer rebates can close the price difference and make the two stg more affordable and attractive. however, without these rebates, you will be unable to justify with a reasonable payback for most new systems. and with a thermidistat or a stat with "dehumidify on demand" feature, you can certainly achieve superior dehumidification for high eff sgl stg AC/HPs in AC mode in areas/climate with high humidity. The main advantage for two stg condensers and particularly the mdls with a 50/100 output split is for applications using zoning controls. I realize NY has high electric rates but strongly recommend you run your numbers on the fuel comparison calculator that I provided a link for. It is a good exercise for anyone considering new HVAC purchase. IMO

I am just being forced to buy a new a/c heat pump unit. My 1988 Carrier unit is finally decided to no longer produce cold air as the condenser is failing. I am replacing it with a 2 ton 15 seer Trane unit with a 2 ton air handler. My house is under 900 square foot and I have 6 windows and one set of french doors. The final cost for replacing the old unit and air handler with a new pad, duct work and a digital control is $4700. There is a tax rebate and since my new unit falls under $5000 I will get $1411 of a possible $1500 rebate. And our local electric company here in Lakeland, Florida will issue a $250 credit on my electric bill. posted date 5/15/2009

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

I realize this is single stage vs. two stage thread. My goal in stating what I stated was to show there is a realm above 2 stage, more or less as well as to show there are differences from one manufacturer from another. It wasn't my purpose to hijack a thread. There are those out there that say 2 speed equipment is unnecessary... so why would manufacturers make 5 stage equipment and variable speed equipment on top of an already unnecessary system? Many times in the field I've heard of people saying 'I don't want to gold plate anything'. Part of my response was geared to show that 2 stage systems these days are middle tier systems. People change homes so much: yes, this is why my job can be really challenging. Many times it's not replacing a whole system (which would be required to go to a 2 stage machine... in most cases*). Many times my job involves retro fit decisions. Replacing one or two pieces of an older system. In situations like that it's more about repairing the existing system and give a homeowner a solution they want. If I find out a home owner is only planning to stay in the home a few short years I rarely if ever even offer the 2 stage equipment. 2 Stage equipment is for those of you looking to stay in the home for at least a decade or longer. HVAC is not a one size fits all market. I am more likely to repair an existing system in some fashion than to replace. But replacement in some cases is the better option regardless of how long you plan to live in the home. If you live in my climate (Katy, Texas), you will have a tough time to sell a home without a functioning AC system.