I have been in my home now for 6mths and my unit is brand new. During the day unit heats my home but at night when the temp has dropped it blows cool air and does not heat the home. What is wrong with it? My air conditioner works fine... it's just the heat.

Exact brand?

Exact model number?

This should be under warranty so it might be better for you to contact the contractor that installed your equipment.