Heating Pads for Flasks

[Afid]

I have a bunch of flasks of Phal. manii, but it is proving to be expensive to keep the room they are in heated all the time, so I have been thinking about getting a heating pad (like those used for reptiles and stuff) to keep them warm. However, I am concerned that the pad might either not provide enough heat or "cook" the seedlings in the flasks. Has anyone tried this before? I'd love to hear any input or advice you have! Thanks in advance.