Return air grilles play a crucial role in the home or office ventilation. The primary purpose of the return grilles is to capture and filter the air outflow and take it back to the furnace.
But does the return grille size on your wall or ceiling matter? Let us discuss the importance of proper sizing of your return air grille in ventilation.
What is the Standard Return Air Grille Size?
There is no standard air grille size. Instead, the capacity of your HVAC output determines the air grille size. Another determinant of the air grille size on your wall or ceiling is the capacity of the air supply in your home. The return air grille should absorb all the air that the air supply grille or register has released.
Most HVAC units have a cubic per meter capacity of (CFM) of 400. Thus Return air grille should have at least 200 square inches. You will find many grill sizes in the market ranging from 4×6 inches to 20x 30 inches.
To determine the air grille size to install in a specific room, you must calculate the CFM of the room. A sitting area, for example, will need a larger Return air grille than the hallway.
How Do You Size a Return Air Grille?
The Return air grille on your wall or ceiling must be of the proper size for your HVAC unit to function well. You can follow the steps below to measure your return grille.
Confirm the Air Conditioning Capacity
Open the cabinet of your HVAC unit to gain access to the service plate. Confirm your furnace’s BTU (British Thermal Units) output on the surface.
Next, you will need to determine how much cubic per meter (CFM) your furnace blows. You can get the CFM by dividing the British Thermal units by 50. For example, if your furnace has a capacity of 40,000 Btu, its output CFM will be 800.
Calculate Filter Grille Size Requirements
Calculate the size of your filter grille in square inches. 2 CFM per square inch of filter grille area is recommendable for proper operation. For example, if your furnace produces 800 CFM, you’ll need a filter grille with a surface area of 400 square inches.
Determine Correct Grille Size
Use the square inches obtained above to determine the correct size of your return grille. You can do this by multiplying the lengths and widths of the standard grille sizes available in the market.
How big do Air Vents Need To Be?
To get the correct size of your return grille, match the grille size to furnace airflow output in cubic feet per meter (CFM). A furnace return system must gather all the air that the furnace produces. For example, the return grille must have the same capacity if the air conditioner generates 1,000 cubic feet of air.
So, the return vents need to have the same capacity as the air generated by the HVAC unit in cubic meters. It is also essential to consider the size of the supply grille. The return grille should be larger than the supply grille. For example, if a supply grille is 4×10-12 inches, the return vent should be 16×20 or larger.
Ensure that the return air filter grille is clean. You may need to change the filters regularly. Dirty filters reduce the efficiency of the return grille.
What Happens When the Air Vent is too small?
Your return grille should be able to accommodate the air outflow from the furnace. When the return grille on the wall or ceiling is too small, the return air duct is too small. As a result, the airflow squeezes when passing through the vents, making an audible whistling sound.
A small return air grille reduces the heating efficiency, increasing energy bills. If a smaller grille is necessary, keep the face velocity below 800 fpm. You can also opt to use more than one return grille to split the air between the return vents.
Can a Return Air Grille be too big?
A return grille cannot be too big unless a closed chamber is under negative air pressure.
Return vents maintain air pressure and filter out waste. The system moves a finite amount of air, that is, the airflow generated by the furnace. As a result, the airflow stays the same no matter how many grilles there are or how big they are.
How to Measure Return Air Grille?
You can follow the following steps to achieve accurate dimensions of a return grille.
Step1: Remove the existing grille
Ensure that you do not measure the existing grille on your wall or ceiling but the actual vent hole. To achieve this, remove the existing grille so that you can access the rough opening.
Step 2: Proper recording of the measurements
While recording the measurements, always start with width followed by the length. For example, if the opening is 4 inches wide and 6 inches long, the correct dimensions of the grille should be 4″x6″.
Step 3: Actual grille measurements
The interior dimensions of the actual air grille will be smaller. The slight variance ensures that the frame fits into the recessed holes. Ensure you have a clearance of about 1 inch in your ductwork to accommodate the variation.
Step 4: Outer dimensions
The actual grille’s outer dimensions will be larger because of the faceplate. In most cases, the faceplate also houses the space for fastening the screws to hold the grille in place. You can measure the exterior of the existing grille to have an idea of what to expect.
Can you have Too Many Return Air Grilles?
Under normal circumstances, you cannot have too many return grilles. Like we have before seen, the return vents can only move a finite amount of air, no matter how many or how large they are. If you add more vents on the wall or ceiling, the system will split the airflow between them. But, the total amount of air recycled will remain the same.
Supply Air Grille vs. Return Air Grille
Both supply and return grilles cover vents but have different functions. The supply grilles cover the duct that supplies conditioned air from your HVAC unit. The conditioned airflow moves from the through supply vent to your house. You can put your palm in front of these vents to feel the air pouring out of them.
The return air grille shields the vents that draw air back into the system for conditioning.
The best place to install supply vents is near baseboards and on the floor because of heat rise. The optimal position to place the air return vents is opposite the supply grilles. This positioning ensures the air circulates well before it goes back for conditioning.
Should Supply and Return Grille be of the Same Size?
No, the supply and return grilles should not be the same size. However, the return air grilles should be larger than the supply grilles for balanced airflow.
Generally, there are more supply vents in your home than return vents. Thus, there is a need for the return vents to be bigger to accommodate all the airflow from the supply air grilles. Balancing between the supply and return of airflow maintains an ambient home environment.
Registers vs. Return Air Grille
Registers supply indoor air into a specific room from the HVAC unit. Unlike the regular supply grilles, the registers have a damper on the grills. The damper allows the airflow into the room and controls the direction in which the airflows. The dampers also shut off airflow from a particular room. Ventilation, then, maximizes in the rooms that need conditioning.
As earlier seen, the return grilles remove the airflow from the room back to the furnace.
For placement, registers are best placed on walls and floors. The return grilles’ best position is opposite the registers, on your wall or ceiling. This positioning ensures complete airflow circulation before it returns to the furnace.
Ensure that the return air grilles are larger than the registers when installing. This placement keeps the airflow in your home balanced.
White Return Air Grilles vs. Aluminum Metal Return Air Grille
A white return air grille is crafted of steel and coated with white paint. The return grille lays almost flat on the wall and hides the openings of the ducts underneath. The white coating also adds to the strength of the grille making it more durable. But, of course, the coating also gives it extra weight.
But, white gets dirty easily and is hard to repaint if the owner should decide to change the outlook of the house.
The aluminum return air grille is light in weight and sits almost flat on your wall or ceiling. It comes in many sizes ranging from 4×6 to 24 by 36. The aluminum metal on the grill does not rust and is perfect for moist areas. Yet, compared to white return air grilles, the aluminum grilles may show some of the ductworks on the wall.
Aluminum has low maintenance requirements and is versatile when fitting with home decor. The grills are also more available at an affordable price.
Other Factors to Consider before Buying a Return Air Grille
Before you click the buy button, you may also want to consider these other factors.
The return grill must have an affordable price that is within your budget. If you are buying online, you can check the price by clicking on the images. The images will also show you the grilles in stock and bought customer feedback.
You also need to consider the material that the grille is crafted from. You can choose between metal, steel, plastic, or wood. While choosing the material, you can also consider the durability of each option.
While choosing the material, you also need to consider the various colors. For example, you can choose between soft white, driftwood tan, or brown. You can also opt for shiny aluminum or steel.
We have seen that the return air grille size is essential in operating an HVAC unit. The return air grille should accommodate all the airflow from the furnace. The grilles come in various come in many sizes. The main determinant of the size of your grille is the capacity of your air conditioner.
Different rooms have varying air capacities. Therefore, you must consider the specific room’s cubic feet per meter (CFM). The medium sizes are ideal for living areas and bedrooms. The hallways and washroom areas have smaller requirements and require smaller-sized grilles.