Your ig needs a UVB lamp set at the right distance from his back, a CHE for warming at night, and a general difference in heat at the cool end and the warm end of the habitat. 80F is good for the cool end, and 95 is good for the warm end. He must voluntarily spend time in both areas throughout the day.
Does he have a good UVB light?
If it's cold (cold to your iguana-below 80) in your house, confine him to his habitat where you have built a good enough temp and UVB range.. He might really want to free roam, but if it's cold in the house, it's bad for him.