I just had a new furnace installed and after 1 1/2 hours the room temp went from 40 to 54 and then seemed to not climb any higher. The air at the vent was hardly any warmer than the room temp so I went to the furnace, put my hand on the plenum and it was barely warm also. I did not have a thermometer with me at the time so I can't give any exact temps. I just thought that the air comming out of the vents should be noticibly warmer. Does this sound normal?