In effect, you are weaning chicks off heat by the end of their first week by supplying them with less.
Look at it this way. You are in a room with a heater. It's set on "high". You are knitting yourself a sweater and you finish it and put it on. Now you are too warm with the heater on "high" so you turn it down.
This is sort of what's happening with your chicks. As they grow in their feathers beginning with the first week, by the end of the first week, they need less heat because they are beginning to grow insulation to hold in their body heat.
This process keeps going through the following weeks, and by the end of the third week, chicks no longer need any heat at all during the day, and only a little bit of heat at night until they finish getting feathers at age four to five weeks.Then they are done with heat all together.
People who don't understand this, keep their fully feathered chicks under heat, and the chicks are probably very uncomfortable and definitely not acclimated to cool temps.
As you are decreasing the heat your chicks are warming under, it also helps to begin lowering the temperature of their cool space as well. Taking chicks outdoors during the day for brief exposures to cool temps helps acclimatize them, and it encourages feather development.
If you successfully wean chicks off heat in this manner, they will be ready to move into their coop without heat by age five weeks.