You’ll wonder why everyone doesn’t do this themselves.
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What you'll need:
TOOLS
Flat-head screwdriver
Utility knife
Wire cutters
Safety glasses
Table saw (optional)
SUPPLIES
Duct booster fan
Screws
Fan speed controller
Zip ties
Aluminum tape
Duct boot (optional)
Prepping to Install a Duct Booster Fan
Photo: Grispb / Adobe Stock
There are myriad reasons why one room feels hotter or colder than the rest of your home. More often than not, dirty air filters or leaky ductwork are the culprits. Your local duct installer can inspect your ductwork and do a pressure test to determine if your airflow issues are caused by duct leaks that need to be sealed. Cleaning or replacing the filter can also vastly improve airflow.
Once you’ve ruled out dirty filters and leaky ducts as the causes of uneven temperature, you’re ready to learn how to install a booster fan in the duct so you can focus on a specific room. If your ducts are smaller than the standard size, you may also need to install a duct boot, which can significantly increase the cost and equipment requirements: the boot itself plus a table saw.
Choose the Best Booster Fan for Your Needs
There are three different types of duct booster fans. The best type for you depends on several factors, such as the size of your floor duct, if you can access the ceiling below it, and your confidence in your handy skills.
The simplest option is the booster fan that sits on top of the register. You don't need to open the floors or ceilings or install boots with this type. You may not need most of the supplies and tools on the list if you go with this option.
Inline duct booster fans are installed in the duct line. They can have simple or incredibly complex installations. Because they can be wired into your ductwork, inline duct boosters offer the most powerful air boosts of all three options. You may need to hard-wire this fan into your furnace with a relay, which you shouldn’t attempt without a local electrician. If it’s a plug-in type like the simple booster fan, you just need to find the right duct.
Recessed duct fans are tucked inside floor ducts. You'll need to measure your floor ducts. The standard sizes are 4 by 10 inches and 4 by 12 inches. If your floor duct is smaller than this, you'll need to cut the floor with a table saw and install a right-angle boot sized to your recessed duct fan. If your recessed duct fan already fits in the floor duct, you don’tneed a table saw or boot.
Put the Simple or Recessed Duct Booster Fan Into the Register
Assuming that your ducts are standard size, go to the room where it's too hot or cold and locate the register.
Simple booster fans: place the fan on top of the register, then continue to Step 4.
Recessed duct fans: Locate the duct register, open it, and pop the booster fan into the boot. Using your screwdriver and screws, screw the booster fan into the floor.
If the ducts are smaller than standard, use the table saw to cut an access panel and remove the duct boot. Install a right-angle boot sized to your new booster fan. This might require removing some flooring. Head to Step 4.
Place the Inline Duct Booster Fan Into the Exhaust Duct
Locate the exhaust duct, disconnect the power, and remove the end cap. If the correct duct is connected to other segments and has no end cap, use a utility knife to cut into the aluminum tape and undo the screws along the duct's seam with the screwdriver.
Insert the inline duct booster fan into the duct, and secure it with screws or zip ties. Put the end cap back on, or replace screws on the duct seams and place new aluminum tape around the seam.
Power the Fan on and Test
Turn the power back on if you just installed an inline duct booster fan. If your electrician hard-wired the fan, test its flow and the on-off switch they installed.
For simple booster fans and recessed duct booster fans, plug the cord into the nearest outlet. Is airflow in the room improving and feeling warmer or colder as desired? The fan shouldn’t make rattling noises if running at high speeds.
Add a Fan Speed Controller
Finish the job with ultimate comfort by adding a fan speed controller to the new duct booster fan. With this controller, you can adjust it to your liking whenever you want on extreme weather days. Sweltering heat wave? Turn it up!
DIY vs. Hiring a Pro
Installing a duct booster fan can make a huge difference in your airflow if you’ve already looked into other potential causes of unevenness, such as dirty air filters and leaky ducts. There is also a wide range of duct booster fans in all three types.
If you opt for a simple duct booster fan that sits on the register, it’s not much different than plugging in a box fan and doesn’t require professional assistance. You also can probably handle recessed models for floor ducts by yourself unless the fan doesn’t fit the boot currently in there. If you’re uncomfortable cutting the floor and handling a table saw, this is best left to professionals.
Inline duct booster fans can be simple to install if you know which duct to place them in. If they’re not the kind that you just plug in like a simple booster fan, you need an electrician’s help. Messing with the wrong wires can be deadly, and hard-wired devices require compliance with local electrical codes. The pros have the tools and know-how when the fan needs more than a simple plug.
Frequently Asked Questions
If you've ruled out other airflow problems like leaky ducts and dirty air filters, air duct booster fans are absolutely worth it. They're a relatively inexpensive investment that can address the weak points in an otherwise functional HVAC system. You can also get an additional level of comfort control by adding a fan speed controller.
Duct booster fans target specific rooms that have more constricted airflow compared to the rest of the home. The control they offer varies by the model, but basic models often have speed adjustment add-ons. More advanced duct booster fans have internal thermostats that let you adjust the temperature in that room. Hard-wired inline duct boosters usually offer more advanced controls than simple register fans.
Booster fans increase the circulation of air that’s already flowing through the ductwork but passes over a weak spot despite no other HVAC issues. They’re in the same room where the user wants to increase airflow. They boost airflow to the room that gets passed over. Inline duct fans are located inside the duct and are much farther from the room, but address the same airflow problem.
Rachel Presser is an experienced writer teaching homeowners how to navigate HOAs, home insurance, and local laws when taking on home improvement projects. She holds both a bachelors and master's in accounting and can explain the income tax impacts of homeowner transactions. Her work can be found in other publications like Home Stratosphere and LA Digs.
Rachel Presser is an experienced writer teaching homeowners how to navigate HOAs, home insurance, and local laws when taking on home improvement projects. She holds both a bachelors and master's in accounting and can explain the income tax impacts of homeowner transactions. Her work can be found in other publications like Home Stratosphere and LA Digs.
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