In a forced air furnace system air is circulated throughout the home by a network of tubing called air ducts. Heated or cooled air exits the air ducts into each room. This air is sometimes referred to as conditioned air–hot or cold. The unconditioned air (i.e. room temperature air or cold air) returns to the furnace via a separate network of air ducts called the cold air return.
At the air duct opening in the wall, ceiling, or floor; a vent cover, grill, or register plate generally covers the opening. Sometimes these covers will collect dirt or become blocked. This is mainly a concern with the return air vents as dust, lint, pet hair, etc. will collect on the fins as air is drawn into the air duct. 
To maintain proper operation the furnace need a constant supply of return air available to the fan. If the air flow to the furnace is restricted then the efficiency is reduced and over time damage may occur.
The following are some tips to ensure good air flow:
1. The most common cause of restricted air into the furnace is a clogged air filter. Regular replacement or cleaning of your air filter is necessary. Remember, a clean air filter makes your furnace happy. For more information about maintaining your air filter, click here.
2. Don’t block the return air vents with furniture, boxes, or other items that will prevent the air from flowing into the return air ducts. If you do have furniture in front of the return air duct then allow 4-6 inches of clearance.
3. In many homes the return air vents are centrally located in hallways or other main areas. Air is drawn from the various rooms to the central vent. When the doors to rooms are closed, air still needs to circulate back to the furnace. One simple solution is to leave a 1 inch gap at the bottom of the door.
4. Clean your vent covers periodically to remove the dust and lint which over time will build up and reduce the air flow to the furnace. We recommend using a brush attachment on your vacuum to try to keep the dirt out of the air duct. Some dirt will invariably enter the air duct during the cleaning process, so a good time to do this is just prior to replacing the air filter in the furnace.
Thank You,
David McGill
James McGill
Article written by Tim McGill, editor@Tree Branch Publishing.
