GRD Terminology
The abbreviation GRD is commonly used for the grille, register, & diffuser (air distribution products) category.
It seems that over time, the terminology has become confused - for example, the term “vent” quite often used as a substitute for any one of the above.
Please note that Grilles are primarily used for return air, while Registers and Diffusers are strictly for supply air.
Grille
A Grille simply covers an opening - allowing air to pass through. It does not have an attached damper to restrict or allow air movement. However, a grille can be used for both supply air and return air. Both
Register
A Register is a damper-equipped grille used for supply air. Generally, Registers are used in residential applications only.
Diffuser
A Diffuser is an air flow device designed to discharge air in a spreading pattern, specific path, or particular direction.
GRD Cross Reference
Part Number(s):
| Grille | Register | Diffuser | |
|---|---|---|---|
| Air Flow | Supply/Return | Supply Only | Supply Only |
| Damper | No | Yes | Most of the Time |
| Directional | No | No | Yes |
| Market | Residential/Commercial | Residential Only | Residential/Commercial |
| Communication Environment | Typical Occupancy | |
|---|---|---|
| < NC 25 | Extremely quiet environment; suppressed speech is quite audible; suitable for acute pickup of all sounds. | Broadcasting studios, concert halls, music rooms. |
| NC 30 | Very quiet office; suitable for large conferences; telephone use satisfactory. | Residences, theaters, libraries, executive offices, directors rooms. |
| NC 35 | Quiet office; satisfactory for conference at a 15-foot table; normal voice 10 to 30 feet; telephone use satisfactory. | Private offices, schools, hotel guestrooms, courtrooms, churches, hospital rooms. |
| NC 40 | Satisfactory for conferences at a 6-to 8-foot table; normal voice 6 to 12 feet; telephone use satisfactory. | General office, labs, dining rooms. |
| NC 45 | Satisfactory for conferences at a 4- to 5-foot table; normal voice 3 to 6 feet; raised voice 6 to 12 feet; telephone use occasionally difficult. | Retail stores, cafeterias, lobby areas, large drafting and engineering offices, reception areas. |
| > NC 50 | Unsatisfactory for conference of more than two or three persons; normal voice 1 to 2 feet; raised voice 3 to 6 feet; telephone use slightly difficult. | Computer rooms, stenographic pools, print machine rooms, process areas. |
| Application | Recommended Face Velocities |
|---|---|
| Broadcasting Studios | <500 FPM |
| Residences | 500 to 750 FPM |
| Apartments | 500 to 750 FPM |
| Churches | 500 to 750 FPM |
| Hotel Guestrooms | 500 to 750 FPM |
| Legitimate Theaters | 500 to 1000 FPM |
| Private Offices, acoustically treated | 500 to 1000 FPM |
| Private Offices, not treated | 1000 to 1250 FPM |
| Motion Picture Theaters | 1000 to 1250 FPM |
| General Offices | 1250 to 1500 FPM |
| Stores, upper floors | 1500 FPM |
| Stores, main floors | 1500 FPM |
| Industrial Buildings | 1500 to 2000 FPM |
Introduction to Grilles, Registers and Diffusers