With a heat plate they wean themselves, at least down to ambient temperature. They just stay away from it as long as they have room to avoid it. How old are yours and what are your nighttime lows? Are they outside yet?
Several times I've had five-week-olds go through nights below freezing. Not bitter cold, in the mid 20's. Mine are raised outside in a big brooder so they are acclimated. The coop has great ventilation up high and good breeze protection down low. It can be a little rough going direct from a tropical climate like the inside of your house directly to really cold temperatures, but I would not hesitate at 6 weeks and a low of 45F as long as the coop had decent ventilation and good breeze protection.
They are 6 weeks. The nighttime lows are about 45 here in VT. They're still in the house as the coop is not quite done (should be done today). The heat is still on in the house and set at 65. They don't seem to use the heat plate anymore at night. I do put them outside to free range during the day and 50 degrees doesn't seem to bother them. I was planning to put them in the coop tomorrow with the heat plate out there until it stays over 55 at night. Does this sound good? The coop has 3" ventilation around the roof line and the walls are insulated below that so they will be protected from wind.