Ambient temps are critical for thermoregulation. Humid hides are the easiest solution to the problem simpler and less risky than using exhaled breath to increase humidity.

Anatomy 101

Snakes have a long lung (many have a small lung too but it is mostly assist for the main lung) The heart, liver and all major arteries and blood vessels pass along that lung. If the air with in the lung is cool the blood will be cooled. Surface temps warming the ventral muscle system may be unable to counter cool air temps. Most keep the ambient air temp at or near 80ºF.

"TEMPERATURE
~80F (ambient temps)
~90F (basking temps)
75 or below is unhealthy"

Quoted from the care sheet from this site. It doesn't matter how you get temps just get them and maintain them.