Currently in the mid-upper 50's around here. Heater kicked on this morning, but that's just par for the course. Believe it or not, I keep the thermostat on during the summer. It still kicks on in early June, and a couple times during the summer.
Why? Because it keeps the cob webs from building up, and I know it will run when I need it. Just like a car that sits too long will have more problems when you run it again, than if you run it off and on.