Well, I cannot call AC a necessity, We just bought it a year ago and before that did not really miss not having an AC. But it does help a lot during summer or whenever dad comes home very tired, he switches it on to get a fresh cool breeze of air.
I can highly recommend a high efficiency heat pump style of central A/C because it is useful year round. In Spring or Fall and on cool Summer mornings it reverses and draws heat from outside air to warm your home. In hot weather, it functions as a normal central A/C. We put in our 2-1/2 ton (cooling capacity not weight) heat pump in 2006 for C$5300. I expect it will last 20 years or so. That breaks down to $265/year, not bad for comfortable living temperatures and because of it's high efficiency, I've seen only a slight increase in our power usage and a lower gas bills in Spring, Summer, and Fall.
