THE ABCS OF AC WHAT TO GET, HOW IT WORKS, WHOM TO HIRE.(Spotlight on Home and Gardening)

Byline: Rebecca Jones Rocky Mountain News Staff Writer

The older we get, the less we believe that if you live in Denver, you don't need air conditioning.

While it's not the imperative that it is in more humid climates, it's still a nice amenity. And if you suffered through one sleepless night too many in a stuffy upstairs bedroom this summer, know that autumn is an excellent time to retrofit your home with central air conditioning.

``Now, because it's not the air-conditioning season, things are a bit cheaper,'' says Dan Hornsby, heating, ventilation and air-conditioning instructor at Denver Technical Institute. ``I'd do it late fall or early spring. If you don't put it in now, at least start planning now.''

What will it cost to install?

The cost depends on a number of factors, including the size of your house, the adequacy of your existing furnace and ductwork, and the efficiency of the system you choose. The new high-efficiency air-conditioning systems cost more initially but use less energy. Expect to pay $2,000 to $3,000 to retrofit a typical Denver bungalow.

What's the difference between air conditioning and evaporative cooling?

Air conditioning cools your …