Air Conditioning Grilles: Everything You Need to Know [Styles, Sizes & Tips]

Your air conditioner’s grilles are more than an aesthetic choice – they help direct air around your home in a seamless process and for optimal performance. With multiple air diffusion grille types available, we’ll show you the difference between styles and how to find the best grille for your home.

One of the most common questions we’re asked by customers looking to upgrade their A/C system is, “what are my options for grilles?”

After you’ve gone through the expense of installing the right ducted or bulkhead air-conditioning system, you want to make sure the visual finish is to the highest standards and works with the aesthetics of your home.

To help you choose the right grille for your A/C system, we’ll break down the most common grille types, including:

  • Custom Aluminium Bar Grilles
  • Ceiling Slot Diffusers
  • Timber Grilles
  • Round Grilles

At iEnergi, we’re experts at integrating grilles into architecturally designed homes, ranging from aesthetically pleasing linear styles right through to round grilles. So if you’re ready to control the temperature of your Melbourne home, and discover a grille aesthetic that suits your tastes, read on for the ultimate guide.

Custom Aluminium Bar Grilles

Aluminium grilles are lightweight and stylish finishes suitable for a range of home styles and A/C systems.

Aerodynamically designed to generate maximum airflow without excess noise, these grilles are the definition of versatile and may be mounted in the wall, sill, ceiling, or floor (so there’s always a way to work towards your air conditioner).

iEnergi Recommendation: For outstanding performance and versatility, consider Holyoake bar grilles – a high-quality, custom fine line bar grille. The 3.2mm vertical bars are mechanically pressed into the rear of the horizontal bars to give a seamless fine line finish with each bar spaced 12.5mm centre to centre. As a proud Holyoake partner, please reach out for support or assistance across the Holyoake range of grilles and diffusers.

Horizontal bars are available in straight or deflection angled, though angled bars are only used in rooms with a high ceiling that requires air to be directed downwards rather than straight. Once horizontal bars are selected, the frame style can be confirmed.

There are a number of frame styles to suit different applications, including:

Flangeless Bar Grille LD1200-FS6

This frame has a straight edge with a reverse angle on the rear. This type of grille is most commonly used above cabinetry or joinery, sitting on the straight edge of cabinetry and finishing into the straight edge of the ceiling.

The reverse angle rear grille also allows for fixing through the face into timber support if needed. This style offers a striking aesthetic finish to the top of joinery units and can be used in ducted systems and bulkhead units.

flangeless frame

Plaster Mounting Frame (PMF) Grille LD1200-PMF

best air condition room

The PMF allows for a flangeless look in a plaster wall, bulkhead or ceiling.

The PMF frame is installed in the wall (pre-plaster) with duct and sheet metal box attached to the rear, and the wall finished with 13mm plaster (finished into the exact opening of the frame).

Once painted, the flangeless grille clicks into the frame for a seamless finish (the grille itself has a small 6mm flange, however, the plaster finish covers any gaps for a flangeless look).

Flanged Bar Grilles LD1200-FS1 or FS5

best kitchen picture

Flanged bar grilles come in 2 types:

  • 17mm
  • 25mm

The flange allows adequate cover for the hole cut in the plaster and is the most common bar grille used in ceiling, sidewall, and bulkhead applications.

Mitred Corner Bar Grilles LD1200-CNR

For the ultimate finish, we can incorporate a mitered corner for a seamless finish between your bar grille and cabinetry or plaster bulkhead. The options include outside, internal and flat corners as outlined below.

Heavy Duty Floor Bar Grilles LDHF1200-FS6 or FS7

This frame style incorporates a double vertical bar for added support – necessary to handle foot traffic in your home or business. The grille is available with a 25mm flange for covering floor cuts or flangeless to allow the floor to be finished to the grille.

The floor bar grilles can be used for ducted airconditioning and also hydronic trench convectors.

Curved Sidewall Bar Grilles LD1200-FS1 or FS5

Dealing with a curved wall? No problem.

17mm and 25mm Flanged bar grilles can be folded to fit neatly into a curved wall. The maximum radius of a curved bar grille is R1000 (r = radius and 1000 = measurement in millimetres, meaning R1000 would form a perfect circle 1000mm wide).

Filter Return Bar Grilles LD1200-FR

Return air grilles will always be the largest grille size as you’ll have the combination of all air from the supply grilles coming back through the return air.

In terms of style, a filter return bar grille offers a more aesthetic finish and complements linear supply grilles elsewhere in your house. This grille incorporates a double frame with a latch that allows for a simple opening swing mechanism for access to a mesh filter for easy cleaning of the filters.

Alternatively, we can incorporate the filter back at the fan coil unit and have a single frame bar grille in any of the available styles (flangeless, PMF, flanged). In this case, careful consideration needs to be made for the cleaning of the filters.

Ceiling Slot Diffusers CSD-25

When it comes to aesthetic ceiling grilles, the most popular option is a Ceiling Slot Diffuser (CSD). Installation is possible in set lengths or a continuous line, giving you the flexibility to suit the aesthetics of your home.

How do they work?

Put simply, inside the slot of each grille you’ll find a curved blade that directs air across the ceiling and down the wall to heat or cool the habitable space (180º air pattern adjustment). Each slot on the CSD delivers a set amount of air with a careful balance of air volume and noise levels, delivering optimal performance.

At iEnergi, we design all CSD grilles to prevent noise levels exceeding DB35(Airah Technical Handbook 2021) – which is equivalent to the level of noise you hear in a library.

You’ll most commonly find 3 slots when opting for this grille type as this provides a balance between length and aesthetics. Case in point, to reduce the number of slots to 2 would require your grille to be much longer, which poses issues for many Melbourne homes that face structural restrictions with ceiling joists and trusses.

PLEASE NOTE: We can install grilles with fewer slots and greater length if space allows.

There are 2 common types of Ceiling Slot Diffusers which we’ll outline below.

#1 – CSD-25: Flanged Ceiling Slot Diffuser (2 Slots with 25mm Flange)

A standard ceiling slot diffuser will have a linear sheet metal box installed in the roof cavity (pre-plaster). Once plastered, the internal opening of the box is cut out and the CSD is attached using springs.

Your grille can match the box size, up to 1200mm in length. And for longer grilles (e.g 2.4m)  there can be 2 boxes above the ceiling with timber frame. This gives a continuous finish on the face of the grille.

#2 – CSDP-25: Flangeless Ceiling Slot Diffuser (1 slot)

This is a specialised ceiling single slot diffuser that’s installed pre-plaster and forms part of the ceiling.

For this grille type, you’ll need to allow enough space for your single slot to service the room. For example, a 4×4 bedroom will require 2.2m of the grille.

For this air diffuser, a frame is installed in the roof cavity (pre-plaster) with a sheet metal box and duct connected to the rear. The plaster sheets are then hung and fit tightly into the frame while the grille is installed and trowelled into the ceiling. The end result is a 25mm slot opening in the ceiling with no grille visible.

Timber Grilles

Looking for a more contemporary or rustic grille?

Timber grilles are an elegant option for blending grilles into the fabric of your home. These grilles can be manufactured to set sizes, or custom-made using the same timber as your flooring or cabinets for a seamless finish.

Timber grilles come in a large range, so we’ve rounded up the most popular and high-performing below.

Custom Timber Cabinetry Grilles


This grille performs best when CNC cut into cabinetry timber by a trained cabinet maker. The grille will cover a sheet metal box served by a duct of a ducted air-conditioning system or cover a concealed bulkhead unit.

In either case, the amount of air from the opening changes depending on the air volume and available space. At iEnergi, we work closely with builders and cabinet makers to confirm the area and space required to ensure that airflow and noise criteria are met.

Some common grille size openings for Daikin FDXS Concealed Bulkhead Units are below. The actual grille lengths are generally longer so as to match up the lines of the room or cabinetry.

    7.1kw Bulkhead     0.132sqm PER 1060mm X 153mm(X2)
    5.6kw Bulkhead     0.118sqm PER 860mm X 153mm(X2)
    4.5kw Bulkhead     0.076sqm PER 860mm X 153mm(X2)
    3.6kw Bulkhead     0.057sqm PER 660mm X 153mm(X2)
    2.8kw Bulkhead     0.055sqm PER 660mm X 153mm(X2)
    2.2kw Bulkhead     0.051sqm PER 660mm X 153mm(X2)


Timber Floor Grilles

Timber floor grilles are factory-made and come in pre-set sizes. They come with a 25mm flange that can have a bevelled edge for surface mount or a straight edge for integration with a timber surface.

timber floor bargrille 1  timber floor bargrille 2

Round Grilles

Round ceiling diffusers are made for long-term strength and rigidity, so while you won’t get the same aesthetic advantages as some other grille types we’ve mentioned, you’ll get a workhorse that provides great coverage for your home.

For our standard grille option, we prefer to use a round grille as these blend in better with the ceiling.

There are 2 types of round grilles that are commonly used in Australia:

  • Eco-A Round Grilles
  • Eco-M Round Grilles

ECO-A & ECO-M Round Grilles

This is an engineered polymer grille that offers a sleek, clean finish and clever engineered features. The front face of the grille is perforated, allowing heating air to be directed straight down into your living space (this can be achieved both automatically and manually).

The ECO-A has a clever bi-metallic strip that will open the perforated face in heating mode. In cooling mode the perforated face closes and pushes air across the ceiling, allowing it to drop naturally. The ECO-M model has the same feature however it’s controlled with a manual switch on the grille face.

Congratulations! You’re an expert in air diffusion grilles. Here’s what to do next…

Choosing the right A/C system for your property is a great start, but the range of grilles available can feel overwhelming.

Grilles, or air diffusers, are a personal choice that should reflect the style of your home or business. At the same time, air diffusers control the speed and flow of hot and cold air, which makes choosing the right product crucial.

You don’t want to end up with a grille that looks great but fails to cool your home. If you’re looking for support, contact the iEnergi team to speak to Australia’s leading air conditioning experts. We’ll suggest the best grille for your home, taking into account your style and airflow needs.

Need help choosing the right grille for your home or business? Request a FREE design brief that tailors the right grille for your heating and cooling needs.