K.I.
My oldest nephew (who was also the 1st kid in the family) was a little sweat ball! He would leave the biggest sweat circle on the pillow, it freaked us out at first!
When he would stay the night and sleep with me, I would keep the ceiling fan on the lowest setting and dress him in the lightest one piece PJ's I could find.
Does he sleep with you or in his own bed?
If he sleeps with you, I would say that being in the middle between you and his Dad probably insulates him pretty well and you can leave the fan on but dress him in something light...
...but if he sleeps in his own room, I would think the fan isn't necessary and let him sleep in just his diaper and a onesie or a t-shirt.
For the most part my nephew was not effected by all his sweating at all...he would just sleep right through it! Do the chills he is having wake him up? Or do you just think he 'looks' uncomfortable? I know I messed with my nephew trying to make him comfortable when in reality he was just fine...he just looked uncomfortable to me...ya know what I mean?