This is what we do when we need the A/C. Most days, we just open the windows. Occasionally, we need to turn it on in the late afternoon until early evening until the temp gets down below the 78-80 we keep the A/C set on.

My neighbor, OTOH, keeps his going 24/7 and has since the spring sometime, no matter what the outside temp is.

Although our house is only 10 years old, it is "old fashioned" in that we have windows on all sides, so we get great cross-ventilation, and lots of trees help provide nature's own A/C.

Also, having lived and worked in WDC and surrounding area for a long time, let me support Dagny's position. DC was built on a swamp, and the heat and humidity in the city can be, and often is, brutal.