If you haven't installed a heat lamp over your chicks by this time, I would expect they would be raising quite a racket because when chicks are uncomfortable, they chirp and screech non-stop. If they're hungry, same thing. So that can be your cue. Once you get a lamp over them, if they still complain, you need to lower the lamp until they go quiet. That means they're content.
You'll see your chicks moving around, sometimes falling asleep like they've keeled over and passed out. That's typical of babies in the first week. They will probably sleep all night, though, unless they're uncomfortable. If you wake up in the middle of the night and hear a lot of frantic chirping, it means they're too cold, and you need to get up and adjust the heat.
If you see all the chicks huddled in a pile directly beneath the lamp, it means they're not warm enough and you need to lower the light. If the chicks are lying around just outside the range of where the light hits, it means the light is too low and the chicks are too warm. You might also see them panting.
But, yes, heat is very important for chicks. They will go into shock and die if they aren't kept at around 85 to 95 degrees the first week. They need less heat every week as they begin to grow feathers, which, by age four or five weeks, will do a pretty good job of keeping in their body heat, and they will need very little extra heat by then.
I just noticed as I submitted this post you posted information that would have been very nice to have when you started this thread. Everyone assumed since you "just got chicks", they were a day or two old. If you had mentioned the chicks were all feathered out already, then saying you were thinking of not bothering with a heat lamp wouldn't have sounded so darned ignorant and irresponsible.
If your chicks are, in fact, "all feathered out" (a photo of them would be nice so we can judge for ourselves if you are making an accurate assessment), then they are probably close to a month old or more, and probably do not need any extra heat if the room they are in is around 70 F.