Jake K. I arrived for a previous customer on one room not heating. I inspected the rooms and found the supply air temperature in all three rooms to be 103-106 deg at the supply vent. The two rooms that are not being used have the doors closed and can’t get good air circulation in the rooms. I inspected the duct work in the attic and found the duct to be connected but is a 6” duct. I did offer to replace per duct run to all three bedrooms and increase it to a 8” duct to obtain more air flow. The attack is a very short attic and can’t have much more insulation blown in over the corner bedroom due to the short roof line. I recommended to leave the doors open to let the air circulate better in both rooms.