My daughter was 3 when she was diagnosed.  They say she is a non-saltwaster, but she does not tolerate heat very well, she becomes overheated when playing sports (mainly basketball), she seems to get sick quicker and take longer to get over things.  She has had two crises in her life and I believe we have avoid crises many times by stress dosing her meds.  It is certainly worth testing your son to see if he has CAH.  We were just lucky our daughter did not experience a crisis before her diagnosis.  By the way, we live in VA and it gets awfully hot and humid here, too.  We’re expecting another day in the upper 90’s, with a heat index of 105.