Hi,
I have a cold air return vent on the floor in my livingroom. For years we have noticed that the cold air return vent blows cold air into the house all day/night. We have had to put towels over it to keep the temperature in the house comfortable. We notice it mostly in the winter months. Our house is very old and we had to replace the furnace under the house about 6 years ago. What can I do to help the cold air stay out?

A cold air vent is not supposed to blow but it should take in air to be heated. If it is blowing cold air out it is time to have someone check the furnace for proper connections or to add insulation to that part of the duct.