Heaven’s warmth, like heaven’s light, is different in different places. It has one nature in the heavenly kingdom and another in the spiritual kingdom. It also differs in each community, not only in intensity but in quality. It is more intense and pure in the Lord’s heavenly kingdom because the angels there accept more divine good. It is less intense and pure in the Lord’s spiritual kingdom because the angels there accept more divine truth. In each community, it varies depending on people’s receptivity. There is also warmth in the hells, but it is unclean.
The warmth in heaven is meant by sacred and heavenly fire, and the warmth of hell by profane fire and hellfire. Both refer to love: heavenly fire to love for the Lord and love for one’s neighbor, and hellfire to love for oneself and love of the world and all the craving that is associated with these loves.
The fact that love is warmth of a spiritual origin can be seen from the way we grow warm in proportion to our love, even becoming inflamed and heated in proportion to its intensity and quality, with its full heat evident when we are attacked. This is why it is usual to talk about inflaming, heating up, burning, boiling, and kindling when we are talking about either the affections of a good love or the cravings of an evil love.
from Heaven and Hell, Section 134