Floor registers and vent covers: what they are, how to choose and replace them

Register, grille, diffuser: what the words mean

A duct system is a collection of airways that distribute heated or cooled air to different rooms in a home. The UF/IFAS Extension, the University of Florida's extension service, defines the supply side as what delivers conditioned air to a home through individual room registers. It describes supply registers as vent-like units in walls, floors, or ceilings where conditioned air blows.

The return side works the other way. UF/IFAS Extension says the return register or grille picks up inside air for reconditioning. It draws that air through a changeable filter to the air handler, which is the indoor unit that moves air through the system. Our guide to a return air vent that is too small covers that side in depth.

RectorSeal, which sells registers and grilles, says a register is simply a grille that incorporates an integral damper to control air volume. RectorSeal says a register's balancing damper lets you open or close the vent and direct the air as needed. RectorSeal says a return air grille typically doesn't have a damper and is not referred to as a register. It says a diffuser is a device that pushes conditioned air in a set pattern, and that diffusers usually sit in a ceiling or wall.

Are floor registers common in Florida?

A 2010 Florida Solar Energy Center paper says slab-on-grade homes are prevalent in hot climates. The paper says these homes are still typically built with duct systems in the attic.

RectorSeal says registers are in the ceiling in hot and humid climates because cold, conditioned air falls. It says registers can be on the floor in colder climates because warm air rises. It also says floor registers appear in buildings with the HVAC ducts beneath the floor.

Our guide to ductwork in Florida explains where ducts usually run in local homes.

How manufacturers say to measure for a replacement

RectorSeal says the size of a floor register refers to the dimensions of the duct opening it covers, not the outer dimensions of the register itself.

SteelCrest Corporation gives the steps in its measuring sheet for registers and grilles. First, remove the existing register or grille if possible. Then measure the actual opening in the wall, ceiling or floor, width first and height second. Its example is an opening 20 inches wide by 14 inches high, which means you order a 20 by 14 piece.

SteelCrest explains why the cover looks bigger than the hole. The frame and damper are made slightly smaller so they fit into the duct opening. The cover's outer framed dimension, or flange, is larger. That way it sits flush on the finished surface and covers the rough opening completely.

If your opening is an odd size, RectorSeal lists custom registers and adapters as options. It also mentions trimming or enlarging the opening. It says that should only be done if it keeps the integrity of the HVAC system intact.

Choosing a style and material

RectorSeal describes several kinds of floor register. Standard registers have adjustable dampers. Decorative registers come in patterns and finishes meant to match a room. Heavy-duty registers may have thicker grilles and stronger frames, for high foot traffic. Flush-mount registers sit level with the surrounding floor and are often used with hardwood or tile.

The same guide compares materials. It says steel registers are often powder-coated or painted to resist rust and corrosion. It says aluminum registers are lightweight and rust-resistant, which suits moist areas. It says plastic registers, often made from ABS polymer, a type of plastic, resist moisture, rust and mildew. It says wood registers can be matched to hardwood floors but may not be as durable as metal.

Noise is worth thinking about too. RectorSeal says rattling and whistling can come from poorly designed, incorrectly sized, or worn-out registers. So a cover that whistles may be the wrong size or simply worn out.

Keep them open and clear

The UF/IFAS guide on duct systems lists furniture blocking registers as one of the common air duct problems. It says to keep furniture clear of air registers and return air vents. It adds that anything that interferes with air circulation will make the system less efficient and potentially lead to problems.

Some people close registers in rooms they do not use. A 2003 study from Lawrence Berkeley National Laboratory found that register closing led to increased energy use for a typical California house. It said register closing is not recommended as an energy saving strategy for California houses with ducts located outside conditioned space.

The Berkeley Lab study says closing too many registers is not recommended because the added flow resistance severely restricts the air flow through the system, leading to safety concerns. One of its examples is that cooling systems may suffer from frozen coils. The study focused on heating in California, so it is not a Florida cooling test. Our guide to an AC freezing up explains what that coil is and why it freezes.

Small leaks around the cover

The opening around a register can leak air. ENERGY STAR says to make sure the connections at vents and registers are well-sealed where they meet the floors, walls, and ceiling. It calls these common locations to find leaks and disconnected ductwork.

UF/IFAS Extension says to make sure registers and vents are firmly attached. It also suggests weather stripping on the inside edge of your registers to prevent air leaks into wall crevices.

A loose cover is one thing. A duct that has pulled away from the opening behind it is another. ENERGY STAR says most heating and cooling equipment contractors also repair ductwork. Our guide to duct sealing and duct repair covers that work.