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Floor Vents: Will Decorative Grilles Affect My HVAC System?

Posted by Gregg on May 16, 2017 1:17:53 PM

floor ventsYou’ve just refreshed the look of your living areas—new paint, maybe new carpeting or refinished hardwood floors. Now your old HVAC grilles don’t seem to fit with the new, fresh look. Or, your grilles just look old and worn and you’re thinking it’s time for a change. But can decorative grilles affect the efficiency of your HVAC system? The short answer is, yes. Here’s why, along with some tips on what to consider when replacing your grilles.

Grilles vs Registers

You’ll sometimes hear the terms “grille” and “register” used interchangeably. In fact, there’s a slight difference. Grilles simply cover your ductwork, whether it terminates in a wall, ceiling, or floor. Registers are grilles with a manual damper that can be adjusted to direct airflow.

The Importance of Airflow

The efficiency of your HVAC system is dependent on adequate and unobstructed airflow. One purpose of the louvers on grilles or registers is to direct the air and send it out with enough force to properly cover the room and mix hot and cold air. Without the proper force and airflow, warm air would rise, accumulating at the ceiling, while cooler air would stay at floor level. Not a good situation for your home’s comfort level.

Measuring “Free Area”

HVAC pros use the term “free area” to describe the area of a grille or register that’s open to airflow. For example, a typical 12” x 4” register that covers a 12” x 4” duct would have a total area of 48 square inches. But the actual “free area” of most standard metal registers is 75% of that, or 36 square inches. That reduction accounts for the border and other areas through which air will not flow. A good target free area to keep in mind is 75%.

Wood vs Plastic vs Metal

Wood registers and grilles have the lowest airflow. Especially if installed over floor vents, wood louvers have to be quite thick to prevent breaking or cracking if stepped on or bumped. That additional thickness significantly reduces the free area, which typically is only 45-50%. Some models are even lower. Plastic models can have a similar issue due to thicker louvers to make them strong enough to walk on. Most metal grilles and registers will be in the 75% free area range.

New System Planning vs Replacing Standard Grilles

If your new-home or replacement HVAC system is designed with decorative grilles and registers in mind, then there should be no concern about airflow. But if you’re thinking of replacing standard grilles or registers with more restrictive models, that can lead to problems. That’s almost always a restriction or reduction in airflow that can affect your equipment (furnace tripping on limit, and coils freezing during cooling). It can also cause other comfort-related issues if you’re not getting consistent heating or cooling. If you’re simply looking to replace old, standard grilles or registers, it’s best to stick with the type you already have. There are many finish options—bronze or chrome, for example—and you can always paint to match your décor.

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Topics: HVAC