Use a 50w bulb on a 10g no more.

this will effectively heat the air to 80-85* from experience.

you can also use a larger one on a dimmer.

my self am using a 150w on a dimmer and its more for light then anything as i have it dimmed to the point where its generating no heat as its not needed.

for my boa since she is aborial. i have a UTH thats unplugged right now and i am using a 150w CHE on a dimmer to heat the warm side to 95* which in turn is keeping the cool side 80.9* spot on. the CHE also does a great job of heating the substrate under it and thus giving belly heat as well as back heat.