what size air conditioner for my 2000 sq ft house?

The tonnage per sq ft is the old school way of sizing. The industry standard is to do a load calculation which takes into account many variables. While I agree with the concept it assumes a perfectly installed and maintained system and also uses an average high and low outside temperature for your climate zone.

It doesn't take into account lifestyle, above or below average temperatures, declining capacity due to lack of maintenance etc...

The problem with going too big is that on warm muggy days the unit will short cycle and not remove humidity effectively. The ideal set up is to have a 2 stage system or two separate systems. That way you get the best comfort using less energy. Good humidity control on warm muggy days and extra capacity for the hottest day when you're cooking for a houseful of guests and kids running in and out.

Obviously these 2 options will cost considerably more up front so if you just can't afford that then I suggest using a furnace or air handler that has an ECM, or variable speed blower motor. They can be set up for maximum humidity control and allow you to use a slightly larger ac than the load calc. will indicate for extra capacity when you need it. Granted, the motor and control will add $500-$700 to the cost of the system but the energy savings will pay for itself in 5 years or less. In addition to using as little as 1/10th the energy to run the motor, it is much quieter, and helps to maintain an even temperature in your home.

30 yrs hvac exp

With out doing a load calculation 3 tons maybe 3.5 if you existing duct work can handle it. There are many factors that go into this. Its best to call 3 contractors out and have them give you price quotes.

Dont tell them anything what the other said and just soak up what ever they say. If 2 of the 3 are on the same page your safe to use the 2 that were similar in sizing. If they all 3 are all different call the most expensive well know company in your area which should be able to size this system correctly.

The other issue is the drive package on your existing furnace if one is present. If you only have a 2 ton blower package, and need a 3 ton drive, the you would need a new furnanace to accomidate the load as well as increasing the supply and return on the exiting system.

This is NOT something you want to guess as as it can go horribly wrong. Remember bigger is NOT always better ! Size the system accordingly based on load calculations not a guess !

General rule of thumb is 1 ton of AC for every 500 sq ft of living space if your home is properly insulated So 3.5 ton unit will be just fine .Ie: 42,000 BTU'S. A ton of refrigeration is 12,000 BTU'S Hope this helps good luck

What is the climate where you live? Do you live in Texas where the temp goes to 110 in the summer or do you live in Oregon where it is mild the year round? Only a local HVAC contractor can give you a meaningful answer.

HOW MUCH DOES AN AIR CONDITIONER COST FOR A 2000 SQUARE FEET HOUSE.

4 ton A/C.

would a basement require less BTUs

2100