What size air conditioner for 2600 square feet?

Many things depend on this answer, so I'll offer you a guestimate. If your home is a single story, 2600 sq ft with 8 ft ceilings, and pretty loose leakage, you'll need approximately a minimum BTU/hr of 31200 BTU's, and a maximum of 62400 BTU's/hr. If it's a 2 story, with 8' ceilings, and average leakage, you'll want a minimum of 20280 BTU's and a maximum of 40560 BTU's/hr. Please check with your local professional to be exact.