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Grille and Louvre Measurements: A Practical Guide
Grilles and louvres are essential components in ventilation and air conditioning systems. However, understanding their measurements and knowing how to select the right size can be confusing. This guide will clarify the different types of grilles and louvres and explain how to measure and fit them correctly.
Types of Grilles and Louvres
There are several types of grilles and louvres, each designed for specific applications:
• Weather Louvres: Typically installed on external walls, these have a built-in insect mesh to prevent pests from entering.
• Standard Egg Crate Grilles: Commonly used in ceilings for air extraction.
• Double Deflection Grilles: These feature adjustable blades to control the direction of airflow. Both the front and back blades can be adjusted to direct air where needed.
Understanding Grille Measurements
Grille sizes can be particularly perplexing because the labelled size often doesn't match any external dimension. For instance, a "350 Grille" may not actually measure 350 mm on any side. Here's how to decode these measurements:
External Dimensions: A grille labelled as 350 mm might measure 330 mm by 330 mm on the front and 395 mm across the outer edges.
Neck Size: The "neck size" is crucial. It's the measurement of the internal area where the grille fits into a duct or opening. For a 350 mm grille, the neck size might measure around 335 mm, fitting over the edges of the ductwork or grille box.
To understand where the 350 mm comes from, look at the internal lip measurements that the grille needs to fit over. This ensures it clears all the internal components and fits snugly into the ductwork.
Fitting the Grilles
When fitting a grille into a duct or grille box:
Measure the Neck Size: Ensure the internal lip measurements match the labelled size (e.g., 350 mm).
Check the External Dimensions: Make sure the grille's outer edges fit within the designated space, considering any additional features like rivets or adjustment screws.
Example: Egg Crate Grille
Consider a 150 mm egg crate grille. The front measures about 130 mm, but the neck size—the distance between the internal lips—might be just shy of 150 mm. The corresponding grille box will have a 150 mm spigot that fits over these internal lips.
Indoor vs. Outdoor Use
Indoor Grilles: Basic egg crate grilles and single or double deflection grilles are typically used indoors for air input and extraction.
Outdoor Louvres: Weather-rated louvres, such as weather L types, are designed for external applications.
Special Grilles
Four-Way Diffusion Grille: This grille sits in the ceiling and deflects air in four directions. It often includes a volume control damper that can be adjusted via a hidden screw. Although labelled as 150 mm, its actual outer dimensions might exceed 200 mm. The crucial measurement is the neck size, which fits the 150 mm grille box.
Connecting Grilles to Ductwork
To connect grilles or louvres to ducting:
Grille Box: Most installations require a grille box. This can either have a spigot on the top or side, depending on the available headroom and space constraints.
Flexible Ducting: Attach flexible ducting to the spigot of the grille box. Ensure there’s enough space for any bends or adjustments needed.
