Since his stroke several years ago, Dave is always cold. It used to be just the opposite. As a result, I kicked on the main forced air system and the den wall unit about a month ago while I could still have the doors and windows open to get the stink out of the house.
Since last weekend, we've been using heat almost daily, to get the morning chill off at the very least. Inside the house it has already gotten down to 61 overnight.
Similar to what Tom stated, even when it's sunny and near 70, this time of year it's typical to have very little air movement, so the house stays cold even with doors and windows open. Also typical this time of year is for the peak temperature to be reached around 4 PM, which doesn't help much when you only have about an hour left before twilight.