Today, we are going to look into a tricky HVAC thing: How to increase airflow to one room?
If you have explored this topic on the internet, a lot of stuff you get for how to increase airflow to one room is about opening windows, HVAC maintenance, and changing filters, just to name a few silly approaches.
We all know that changing filters keep our HVAC units healthy. This is the first thing we think of doing when trying to increase airflow to one room. Homeowners that want to get more air in the individual room have probably already checked if the filters are dirty:
If we need to increase airflow to just one room (with airflow in other rooms remaining the same), changing clean filters won’t help. HVAC maintenance won’t help. Admittedly, opening windows will help a little bit due to a decrease in room pressure (and an increase in the difference between the air pressure in the ducts and in the room).
Here’s the thing:
Increasing airflow to one room specifically is not all that easy. There are 3 valid approaches that can increase airflow to just one room. You will have to check if the airflow in that one room is indeed too low. You can check all the tell-tale symptoms of not enough return air in your home here.
Example: Let’s say that a 200 sq ft room has a 150 CFM airflow currently but we want to increase it to 200 CFM. We have only this room in mind; we don’t want to change the airflow in other rooms as well. You can increase the airflow to 200 CFM using one of these 3 methods (or a combination of them).
The goal here is simple:
How to increase the airflow from vents in the individual room specifically?
Let’s check out these 3 methods that specifically increase return air in one room:
#1 Enlarge Vent To Increase Airflow In One Room
Return vents bring air into your room. The larger the return vent, the more airflow you will get.
What is key to understanding here is that the air pressure in the ducts is constant (or thereabout). If you increase the size of the return vent, the drop in air pressure in the ductwork will be insignificant. However, with a larger return air vent area, more air will be able to flow to one room.
This has a lot to do with a constant face velocity; this is the velocity of the air coming from the ducts. In most HVAC calculations, we presume that face velocity is 500 FPM (feet per minute). We use this presumption, for example, when calculating return air grille sizes in CFMs.
Example: Let’s say we currently have 150 CFM airflow in one room. We want to increase it to 200 CFM. If you consult the duct sizing chart here, you can see that a 12×4 duct, for example, is able to allow for 150 CFM airflow. We can also see that the 16×4 duct allows for 210 CFM airflow. If we replace the 12×4 duct with a 16×4 duct, we will get 200+ CFM in that one room.
This is the most effective way to adequately increase airflow to one room.
Of course, resizing these return vents is not all that easy. You usually have to enlarge the area for a bigger vent in the wall which involves drilling.
If you want less drastic approaches to increasing single room airflow, you can try this:
#2 Close Vents In Other Rooms To Increase Airflow In One Room
Without enlarging the return air vents, you only have one other choice:
Increase the face velocity of these vents. That means that you will have to increase the air velocity, and you do that by increasing air pressure inside the ductwork.
How do you do that?
You shut off unneeded vents in other rooms in your house. For example, if you close the vents in the attic, basement, utility room, or some other room where you don’t require ventilation all that much, you will increase the air pressure inside the ducts.
With higher air pressure, the airflow in that one room where you want to increase airflow will increase. Of course, airflow from other opened ducts will increase as well. That means that this method is now as specific as enlarging the vent size.
Nonetheless, if you don’t want to drill into your walls, but still want to increase airflow in one room, this is the way to do it. It’s not ideal that the airflow in other rooms increases as well but it’s usually a small price to pay if you indeed need more airflow in a specific room.
#3 Yes, Open Windows, Doors, Even Clean Air Filters
These are the most obvious, yet the least effective options for increasing the airflow in one specific room.
Cleaning air filters is always recommended. With less dirty filters, the airflow will increase. The increase of airflow, of course, depends on how much the dirty filters dampened the initial airflow. Most homeowners already know this and have cleaned the air filters before looking for other ways how to bring more air into one room, however.
Opening windows and doors is a valid method as well. If you open windows and doors, the air pressure in that one room will likely fall. That means that the difference in air pressures between the ducts and the room will increase (air pressure in ducts is always higher than in individual rooms).
The drawbacks of these simple methods include:
- You will lose cooling/heating through the window. By opening a window, you expose your room to outdoor temperatures. It’s not all that smart to run an air conditioner with open windows, right?
- Effect is quite insignificant. You will see more airflow to an individual room if you open a window in that room, but the increase won’t be from let’s say 150 CFM to 200 CFM. It will likely be to 160 CFM or 170 CFM.
People like this method because it’s the easiest. You don’t have to drill into a wall and install bigger vents, nor do you have to close other vents.
Nonetheless, it is important to understand that opening a window is rather ineffective at increasing airflow into a specific room.
We hope that this illustrates the challenges of channeling more airflow into one room represents and options on how to best increase airflow.