I don't have an answer but it is strange that I am searching for this topic because of an experience I had with heat...on the back of my neck at nearly 3:00 a.m. This morning. I too am prone to "things spiritual" but that was weird. I have experienced the sudden draft of cold out of the blue but in this instance I knew a presence was there but, of course, I couldn't see anything. I felt heat, as if a heating pad had been placed on my neck but only when I turned away from the window. The first thing I noticed was movement of my drapes but there was no air circulating then the heat. When I said to myself, "I don't have time for this", it went away. So I guess my answer is, I believe they (spirits) can manifest in nearly any way they choose. Why heat? I guess we can keep waiting on someone to answer.