Do you know what size condenser is being proposed? I don't think you will notice much difference for a 2 ton size, but you should for 3 tons.

What are you doing about heating?...what size are you replacing?...since home is older and has poor insulation qualities, I would go with a quality single stage AC condenser.

IMO

With lots of leaks, you want good humidity control. That means, at minimum, a variable-speed blower. Are you planning improvements in air sealing and insulation? If so, you will be oversized wrt cooling when you finish and a two-speed might make more sense.

What is the definition of poor insulation and why would it not work well with a 2-stage AC?

Thanks all. Some further info:

- Heating proposals are generally 2-stage gas furnace at 95% efficiency.

- We are looking at 3 ton condensers, matching the unit being replaced.

- Realistically, we probably won't do home improvements to significantly improve sealing and insulation, though we will look for low hanging fruit. We're not sure enough we'll be in house long enough for the insulation investment to be worth it.

- Re insulation, the house is brick without any meaningful insulation between the brick and the walls. We also have a few rooms with quite big windows, so there's heat loss there, too.

insulation in attic is what is being questioned.

can you tell us what type & how much insulation is

in the attic?

I believe it's fiberglass batts, but not positive--at work now and can't visually inspect.

A two stage system is nice and the efficiency of the Infinity system really can't be beat in a conventional system, but WOW, what a price! I have written some articles on choosing between a moderate efficiency system and a high efficiency system. If you're interested, you can read them HERE, but here's my two cents as a guy that makes his living installing AC units. It really sounds to me like you might be better off having a 14 SEER or a 16 SEER single stage unit installed and taking the difference between that and the Infinity system and investing it in insulating and sealing your home. I think the payback will be much better and your home will be much more comfortable. Also, be sure to have a Manual J load calculation done before the equipment is installed. By the way, the two stage 95% furnace is a great idea. I also have a couple of articles on that as well. Sounds like you're off to a great start and have done your homework well. Best wishes.

Sounds like you don't intend to do a lot of sealing and insulation and may not be staying in the house much longer. In which case go for a simple 14 SEER single stage. It'll work just fine, if not the most efficiently. The Carrier Performance series is a lot quieter than the less expensive Comfort series (don't believe their noise specs - these are weighted to the point of being meaningless)

if the return on investment is too long for a 16 SEER AC then wouldn't it also be too long for a 95% gas furnace? The location is Maryland where winters are not harsh but summers can be.

Paying for a 2-stage condenser is more about comfort than energy savings. It is a great feature in humid climates.

I'd have to agree with mike-home on this one. A two stage condenser matched and installed properly with indoor equipment and duct work cuts thru humidity like a hot knife thru butter.

If you're in a humid climate there is nothing better. If your current system is older it's very common to get a decent payback in reduced utility bills over the life of the 2 stage system the bonus is the comfort.

There is also the "health" of the structure and effects of that on the health of the occupants. MD is not as hot and humid at the Gulf of Mexico coast where I am so I don't know how much this applies. The dew points are so high here that the inside of the house is below the dew point a good deal of the time. (The dew point this moment is 76F and it will be in the mid 70s all week.) That means that condensation on parts of the structure is possible with a low thermostat setting. A properly-designed and built home in this environment dries to the inside. If it is too humid on the inside, not much drying occurs. In addition, lower indoor humidity allows the thermostat to be set higher bringing the temp above or nearer the dew point which will cut condensation. Condensation allows mold to grow. This is bad for the occupants if indoors.

Everyone - Thank you so much for taking the time to share your expertise. It's been a tremendous help to us as we wade through our options.

More complex sytems cost more initially, may have more possible points of failure and will cost more to fix when they break. And of course all of them do break.