Do not be fooled into thinking that you never need air conditioning in Newport, VT.
These past few summers there were many days when the temperatures were well into the 80's and 90's, even into September. There is not always a breeze off the lake, in fact, during a heat wave it can become more humid because of the lake.
If you are someone who is not bothered by heat, then you may do fine without A/C. No matter how hot it gets during the day, it almost always cools down at night for sleeping. However, if like me, you wilt, become lazy, don't want to move, and are overall miserable and cranky when inside temperatures rise well into the 80s/90s, then opt for accomodations with A/C.
You may not need air conditioning during your stay, but if there is a day or two that you do, you will be happy you have selected accomodations that have it. My philosophy has always been "better to have it and not need it than to need it and not have it."
If you decide you want A/C, don't assume accomodations have it. Most in Newport, VT do not. Ask and be sure. Don't let a few hot days, or a heat wave, spoil your vacation.