Given that warm air rises, the most logical place to put a heating vent would seem to be on the floor. While it's true that a floor heating vent can create a desirable pattern of warm air circulation in your home, vents must be in the right location to maximize their effectiveness. Improperly positioned vents are inefficient and may make your home much less comfortable than it could be.
The traditional strategy for floor heating vent placement puts the vents near the walls around the perimeter of the home. As the warm air rises from the vents, it moves vertically along the walls and spreads toward the interior of the building, mixing with cooler air near the exterior walls as it goes. This method has the advantage of delivering warm air to the areas of highest heat loss first, which helps to warm the cooler air at the building's perimeter and reduce drafts caused by air leaks in the building's envelope.
Floor vents are also often located directly under windows. A relatively high degree of heat loss occurs at windows, and the air adjacent to the window will likely be much cooler than the air elsewhere in the room. Cool air near the glass sinks and spreads along the floor, potentially creating a draft. The upward flow of warm air from a vent under the window warms the air in front of the glass, eliminating drafts and moving cooler air away from the floor.
Although placing vents along the floor at the perimeter of the building works well if the airflow is unobstructed, the function of floor vents is severely limited if the vents are covered with furniture, rugs or any other obstruction that limits airflow from the vents. At best, the vent's ability to create adequate air mixing and heat circulation will be reduced; at worst, the flow of heat through the vent may be blocked entirely. Consequently, floor vents should never be placed under cabinets or where obstruction by furniture is unavoidable.
Floor vents in bathrooms are especially problematic. Water spills or leaks may drain through the vent and into the heating ducts, causing rust or mold growth in the duct system. Metal vent covers may also have a tendency to rust in the high humidity of bathrooms. Where a bathroom floor vent is necessary, a plastic vent cover is a good alternative to a metal cover.
- U.S. Department of Energy: Advanced Strategy Guideline -- Air Distribution Basics and Duct Design
- This Old House: Placement of Heat Registers
- Rock Wall Controls: Properly Designed Air Distribution Network
- State of Oregon: Design Considerations for Bathrooms
- Lowe's: Decorative Floor Register Buying Guide
- Photo Credit Jupiterimages/Goodshoot/Getty Images