So far used:
Hot washcloth (warm up), spacer heater with 3 lamps (constant heat) and electric heating pad.
Electric heating pad (those used on the knee) is good for pumping, to wrap around the tube. It is crap to warm up for example, it is too big and don’t make enough contact to the skin.
Spacer heater is good to use while doing manual work, like jelqing and stretching. Not so good to warm up with it.
Hot washcloth strictly for warm up. Hot water and steam is showing to be excellent to penetrate deep on the skin. Without doubts, heat is way more effective in the wet version.
A while ago Walter was talking about “hot water stream” (not static water) to be an outstanding way to warm up. Did once and it is something special, but out of the bounds for me right now, since I PE in my room.