How to Size HVAC Registers
Trying to find the right HVAC register for your project? The most common point of confusion about HVAC grilles is how they are measured. The dimensions that suppliers and manufacturers list when talking about HVAC registers is the size of the vent area, not the size of the plate area. The reason for this is simple. When people are building homes and apartment buildings, they are buying both the registers and the ducts together. So, an 16” by 6” duct goes with an 16” by 6” register. Pretty straight forward, right?
Well, as with many product in construction, sizing is a half inch less. In addition, to mount a register, you need extra spacing on the edges. That’s why a traditional 16” by 6” register is actually 17.75” by 7.75” when measured edge to edge. That extra space around the edge gives you plenty of room to mount the register to the wall.
The other question often asked is if you should buy a 2-way or 3-way register. That’s actually a more complex question. For exact details on calculating air flow rates for different room sizes, reference the Air Conditioning Contractors of America, Manual D. Why all the math? When manufacturers design HVAC systems, they try to make them as efficient as possible. This means adapting the air flow to the room. All registers will work with all rooms, but it is less efficient to use the wrong one.