Murmur has 7 cooling damage per turn (when maxed).
I believe Nemo has 12 max heat damage (when maxed) as well, leading to 48 effective heat damage per turn.
Clash is good if your heat build focuses more on damage, and uses heat as a secondary bonus effect.
There's another heat drone?
Edit: Ok I found it, it's called Swoop, it does high heat damage and has some resistance drain to boot, but costs energy to fire.