Demystifying GRD Submittal Sheets

GRD Submittal Sheets

A well-designed HVAC system is critical to building comfort. But within that system lies a network of oft-overlooked components: grilles, registers, and diffusers (GRDs). These control the flow of conditioned air, silently shaping your space's temperature and air quality.

Understanding GRD submittal sheets is essential for those involved in specifying or approving HVAC equipment. These documents provide information about a project's proposed grilles, registers, and diffusers. If you are new to reading them, they can seem intimidating. Worry not! This guide will equip you with the knowledge to decipher these technical sheets confidently.

GRD Basics: A Quick Refresher

  • Grilles: These allow air to return to the HVAC system, typically found on walls or ceilings.
  • Registers: These control airflow but often include a damper for adjusting the volume. They are used on the supply (supplying conditioned air) and return sides.
  • Diffusers: These more complex devices distribute conditioned air in a specific pattern. They are crucial for maintaining thermal comfort and minimizing drafts.

Breaking Down a GRD Submittal Sheet

Contractors, engineers, and architects use submittal sheets to communicate with each other in a formalized, documented way. A contractor can scan the submittal for specifications and substitute products or make recommendations as needed to obtain the correct items for a project.

The specific format of a GRD submittal sheet can vary by manufacturer, but they follow a similar structure. Here is a breakdown of key elements:

  • Product Information: This section identifies the proposed GRD's manufacturer, model number, and type (grille, register, diffuser).
  • Dimensions: Look for the core size (the actual opening) and the overall face size (including the frame).
  • Performance Data: This section contains tables outlining the GRD's performance at various airflow rates (cubic feet per minute, or CFM). Key metrics to look for include:
    • Throw Distance: How far the conditioned air travels before significantly dropping in velocity.
    • Static Pressure (or Pressure Drop): The air pressure difference between the supply duct and the room.
    • Noise Criteria: The sound level generated by the GRD at different airflow rates.

Selecting the Right GRD

The information you gather from a submittal sheet lets you assess if the proposed GRD meets project requirements. Consider factors like:

  • Room layout and size: Throw distance is crucial to ensure that conditioned air reaches all areas of the space.
  • Airflow requirements: The GRD should be able to manage the designated CFM without excessive pressure drop or noise, which can restrict airflow and reduce efficiency.
  • Aesthetics: Consider the visual impact of the GRD style and finish.

Finding the Perfect Fit: Determining Duct Opening Size

Duct openings, the gateways between your ductwork and the room, allow for efficient airflow. An improperly sized opening can lead to problems, from uneven temperatures to noisy operation. How do you determine the correct size for a duct opening?

1. Sizing Based on Existing Ductwork

Measure the duct: This is the most straightforward approach. Measure the width and height of the existing duct opening (not including the frame). This measurement will be the minimum size for your register or grille.

Matching the register and/or grille:  Once you have the duct dimensions, consult the manufacturer's specifications for compatible registers or grilles. These typically list the core size (the opening that matches the duct) and the overall face size (including the frame).

2. Sizing Based on Room CFM Requirements

Calculate the room’s CFM: This method involves calculating the Cubic Feet per Minute (CFM) of airflow required for the specific room, which depends on factors like room size, insulation level, and climate.

Select a register and/or grille based on CFM: Refer to the manufacturer's performance data for registers and grilles with the CFM in hand. Look for tables that show the GRD's CFM capacity at different pressure drops.

Additional Considerations for the Duct Opening

As mentioned before, do not neglect considerations of throw distance and noise levels. Ensure the throw distance is sufficient to reach all areas of the room for even comfort. Choose a GRD with noise levels that meet your comfort expectations, especially for bedrooms or quiet areas.

A Practical Example: Deciphering TRUaire’s LD Series Submittal Sheet

Let’s look at RectorSeal’s TRUaire LD series, specifically the extruded aluminum linear slot diffusers. 

At the top left is basic information like model and size to identify the specific product. Underneath that is a space for project information, including job name and location, followed by submittal information for approval.

The complicated part comes next with the technical data and product specifications for measuring and planning the installation of the product. The contractor can use this information to answer these questions. Say we’re working with TRUaire’s LD24A2. 

Refer to Figure 1:

The measurements in the product image (Figure 1) show us widths for A, B, C, and D.

Dimension A is the width of the back side of the diffuser where the screws are going through it.
Dimension B is the distance between the flanges.
Dimension C is the width of the ceiling opening, or what size opening the contractor needs to cut for the opening of the diffuser to slide into.
Dimension D is the width of the plenum opening.

S refers to the width of the slot opening. For the TRUaire LD series, RectorSeal offers three width sizes: ½”, ¾”, and 1”.
What size diffuser do I need for my opening?
You will want to measure based on the opening that will be made in the wall, not based on the product itself. 

C = Ceiling opening, so go to the charts based on the S dimension to find length and slots. This is an A model, so we will use the first chart at the top (“A” Model Designator): S = ½ inch. From there, the top row indicates the number of slots. Our model A has 2 slots—go the 2 column. We are looking for the ceiling opening, so slide down to the C row: 3 ¼ inches. The ceiling opening for this specific model should be 3 ¼ inches.

What size plenum do I need to connect to the diffuser?

Follow the same steps as with the ceiling opening—we’ll use the same first chart at the top for our A model. D = Plenum opening, so instead of the C row, we’ll look at the D row. Under the 2 column (remember, our A model has two slots), D equals 3 ½ inches. Our plenum opening is 3 ½ by 24 inches with a ½ inch flange at 30 degrees x 2 (as indicated in the Figure 1 drawing.

Where’s the expanded data for your linear slot diffusers?

The linear curve of performance data is based on the length of the diffuser and the number of slots. The airflow will double when the length is doubled—or double the slots, double the airflow. Every time a slot is added, the same values are added. You can multiply the single-slot airflow by the number of slots.

When in Doubt, Consult a Professional

While these methods offer a good starting point, determining the optimal duct opening size can involve complex calculations. Consulting with a qualified HVAC professional is highly recommended for critical applications or new installations. They can thoroughly analyze your space and recommend the most appropriate duct opening size and GRD type to ensure optimal airflow and efficient HVAC operation.

Need additional support? Contact RectorSeal’s outstanding technical customer support for exceptional assistance with on-site job requirements and project specifications.

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