I don't really worry too much about the temperature of the actual paint itself, but you do want to keep it inside if the temperatures are going below 50 at night. Also, you don't want to leave the paint in the sun. I don't know why anyone would say that the paint should be heated. I don't have a problem painting in 80 or 90 degree temperatures as long as you are not painting in direct sunlight or painting objects that have been subjected to direct sunlight recently. If you paint something that is too hot, the paint may dry on contact and won't have a chance to bond properly. This could mean peeling. My ideal painting conditions are about 58 degrees and cloudy, but 70 is fine too.