I only have terrestrial T's right now and use heat mats to increase the temp in their cages. The mats are only on one end so that they have a warm end and a cooler one. This only brings the temp up to about 75f, but they must like it because all of them use the warm end at lest part of every day. It reminds me of behavior in lizards. I would think that a temp of 75f - 80f would be fine for most T's. It may even keep them a little more active.
You wanna be careful with heat mats for ground dwellers because they dig to escape the heat and that would put them closer to the heat if the heat mat is on the bottom. I don't use any heat source for any of my T's. Room temp is fine for any and all species of tarantula.