How Well Do Duct Boosters Work?

If you have ever faced a problem with uneven temperatures or poor ventilation in your house, you have probably stumbled upon duct boosters as a possible fix. But are they worth a try? 

Duct boosters can work exceptionally well to increase airflow in your house and help optimize your indoor air quality. However, there are also scenarios in which booster fans cannot help, and that might be the time to call in a professional to inspect your installation. 

In this article, I will cover how the different types of duct boosters work and what you should consider if you want to install some in your house. 

How Does a Duct Booster Affect Airflow?

Let us start with the basic principles of how a duct booster fan works. 

Duct boosters affect airflow by helping to move conditioned air to rooms distant from the heating or cooling sources in your installation. The airflow to these spaces can be leveled, thus creating an even temperature for the entire household. 

The way a duct booster fan works is not too different from the principle with which ordinary fans operate. They are electrically powered and consist of blades that rotate and give the air in your ductwork a pump.

The booster fans can be programmed to work at a constant capacity or “instructed” to switch on if the air falls beneath the desired cubic feet per minute (CFM) value. 

I will talk more about CFM and other metrics you should be aware of when purchasing a duct booster fan, but first, let us see the different kinds of devices available and their characteristics. 

Read: Does Ductwork Need To Be Sealed?

Types of Duct Booster Fans

There are two main types of booster fans available for household installation: the register booster and the inline booster (also called a mid-duct booster). 

I look at both by analyzing their main features, ways of installing them, plus their most significant advantages. 

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Register Booster Fan Overview

The register booster takes its name from the point where you install it. In a Heating, Ventilation, and Air-Conditioning (HVAC) system, the register is a special vent that contains dampers that give you the ability to control the airflow at that end of your ductwork.

This means that the fan’s blades are situated directly inside the room where you want to improve the quality and velocity of the airflow. 

Here are the main things to know when purchasing a register duct booster:

  • Easy installation. Register vents are usually placed on a room’s wall, floor or ceiling, so you can easily take out the grill and plug in your booster fan.
  • Low cost. Register boosters are usually the most low-budget option on the market. 
  • Low reliability. This again depends on the model, but people tend to report faulty behavior in register fans way more than in inline ones.

Read: Should Ductwork Be Insulated?

Inline Booster Fan Overview 

You install mid-duct boosters inside your ductwork. The usual place is somewhere in the middle of a long duct so that the fans can pick up the conditioned air from the source and increase its velocity. Thus the air can reach the endpoint with the same quality it had when coming out from the source. 

Below are some of the main features you can get with an inline booster fan: 

  • Complex installation. Having to place the fan inside a duct means there are risks of compromising your entire ductwork. You may also need to rip up a wall or outside insulation if you had your ducts sealed after installation. 
  • Higher cost. Inline fans are generally more powerful but also cost more than registered boosters. 
  • Reliable and silent. Mid-duct boosters usually last longer and are more silent than other options on the market. 

Read: Is Ductless Heating Cheaper Than Gas?

How To Choose a Duct Booster Fan?

It can be hard to decide on the perfect duct booster fan for your needs. As you can see, there are a lot of factors to take into account. 

If you don’t want to spend too much time on installation time and are not a DIY person, calling a professional would be your best bet. Getting a specialist to explore your installation and consult you on your duct booster needs can save you time and money.

However, if you are open to learning more about what can help you choose a booster fan yourself, here are some guidelines you can follow.

Calculate the Booster Power You Need

I briefly touched on CFM (cubic feet per minute), which is one of the first characteristics you will see when buying a duct booster fan. Let’s delve into how you can calculate the booster fan power you need to keep rooms at the temperature and air quality you desire. 

You need to first understand and follow the official air exchange per hour (ACH) guidelines. 

ACH is basically the time needed for your HVAC system to completely replace the air in a room with newly conditioned air coming from your heating, cooling, or ventilation source. 

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends that there be no less than 0.35 air changes per hour in any room of a household. 

So, this is what you can do if you want to find out what kind of power to go for with your booster fan: 

  1. Measure the length, width, and height of your room. Let’s say you have a room that is 15 feet (4.57 m) long, 15 feet (4.57 m) wide, with an 8 feet (2.44 m) high ceiling. 
  2. Multiply the values of the three dimensions to find out the volume of the room in cubic meters. 15x15x8 equals 1,800 cubic feet (50.97 cubic meters) of volume. 
  3. Figure out how many air changes per hour you want for the room and multiply the number by the volume of the space. Suppose you want six air changes per hour, so by multiplying 1,800 by 6, we get 18,000 cubic feet (5486.4 cubic meters) of air per hour. 
  4. Divide the value you got in step 3 by 60 to determine the final cubic feet per minute value you need from your duct booster fan. Since we got the cubic feet per hour, we now need to divide 18,000 by 60 to get the final CFM, which is 180 (5.1 CMM).

So, if you want to keep the room in the above example well heated, cooled, or ventilated, you need to find a booster fan that can produce at least 180 cubic feet per minute or 5.1 cubic meters per minute of air exchange. 

Read: Should Ductwork Be Replaced After 20 Years?

Analyze the Severity of the Problem

Even if you have a good understanding of duct booster features, installing the device can be challenging. 

That’s why it is essential that you first analyze the actual impact of the problem. So, ask yourself the following questions:

  • Do you have several rooms with uneven temperatures or just one?
  • Are they far away from the HVAC source? 
  • Do you have compact ductwork or a line that runs longer? 

Answering those questions will give you a better idea of what you may need to correct the faults.

For example, if you only want to improve the air quality in a bathroom, then a moderately cheap register booster with 65 to 80 CFM (1.84 to 2.27 CMM) capacity will do the trick for you.

However, if there are several rooms in your house, all of which are far from the HVAC source and cannot heat or cool properly, you may be looking at a scenario where several inline boosters are needed. 

Consider Your Comfort at Home  

Last but not least, duct booster fans emit noise, so this is something to consider if you’re going down that route.

If you decide to buy one, look out for the value of dB shown on its feature list. This is the level of noise calculated in decibels that the fan will produce when active. 

According to the US Environmental Protection Agency, noise should not exceed 45 dB for people to go about their daily routines at home without disturbance. 

So, it would be best to look for models that can guarantee no more than 35-40 dB when working at maximum capacity. 

Read: Ducted Vs Ductless Heat Pump


Duct boosters can be a convenient way to correct the temperatures and air quality in your house as they are cheap, easy to install, and help push conditioned air more effectively. 

However, they can also prove insufficient, which should not instantly be attributed to the fans. You might be looking at a more complex issue that requires a professional to examine your installation.

So, my advice would be to consult a specialist if you think you have an airflow problem, as duct boosters are not always the correct remedy and can temporarily mask a significant fault in your HVAC system.