The furnace is 8 years old... this is our first year in the house. We set the thermostat at 64 degrees... house is about 1200 sq ft... the furnace will run fine... keep the temp at 64, then it will just stop working... temp may go down to 61 or 60, then will just start running again. Have been told by a friend that the furnace is too big for the house. Suggested we add a vent in basement because he feels it overheats and then has to cool down before it will work again, but the new vent hasnt' really helped. Do I need to put in a new furnace?