Founder | BPI® Energy Auditor Certified Professional
Technical Editor | HVAC Tech at Kearns Heating and Air
Central HVAC systems are comprised of supply ducts and return ducts to circulate air throughout your home.
The aptly named “supply” ducts supply your home with warm or cool air, depending on if you are operating your furnace or air conditioner. These vents are located beneath exterior walls and you can feel air coming out of them if you place your hand on the vent.
Return ducts and vents are used to ensure air has a way to circulate back through the system.
Jumper ducts (AKA jump ducts) are part of the return system, though they are not connected directly to the return ductwork.
They facilitate the flow of air from one room to another. Essentially, they shorten the distance air travels and minimize energy losses due to friction and heat exchange.
Jumper ducts can be an effective way to allow air to flow back into the return system so your central HVAC system works as designed. Let’s take an in-depth look at them.
Jumper Ducts in HVAC: What Are They and How Do They Work?
A jumper duct is an insulated, flexible duct that runs between two rooms in a home. It’s usually positioned in the attic and takes up very little space.
Jumper ducts work by allowing air to flow from one room to another. This is often done if one room does not have a dedicated return air vent.
There needs to be some way for air to move out of the room if the door is closed.
Sometimes this is done by undercutting the door or adding a grill through the wall. Unfortunately, those options can feel invasive and allow significant noise transfer between the two rooms.
Jumper ducts are more discreet than wall grills and they don’t have the same energy losses that you would see if you installed a dedicated return.
Why Jumper Ducts Are Efficient
According to the University of Florida, a typical duct system will lose up to 40 percent of its heating or cooling energy. The energy loss stems from the following:
- Air leakage
- Conduction
- Convection
Jumper ducts can move air from one room to another without connecting to the central HVAC system ductwork.
Less ductwork connected to the central system means less energy loss through that ductwork.
How To Improve Duct Efficiency
Installing jumper ducts when possible is a good way to maintain duct efficiency.
Unfortunately, issues that can thwart even the best ductwork include:
- Thermal losses
- Airflow losses
- Airflow restrictions
The best way to prevent these issues is to regularly clean your ductwork and inspect it for air gaps and leaks.
If you are handy, you can often seal duct leaks yourself with a few supplies from your local hardware store.
When choosing a company for duct cleaning, make sure to vet them properly. Many “duct cleaning companies” only remove vents and vacuum a little bit inside. A proper duct cleaning will require industrial duct cleaning equipment.
Other ways to improve HVAC efficiency are as follows:
- Increase filter size
- Inspect and repair ductwork as needed
- Install air-balancing dampers
- Utilize zoned heating and cooling systems
Principles That Govern Effective HVAC Air Duct Design
There are five principles for designing an HVAC air duct system to ensure efficiency and effectiveness.
Maintain Good Airflow
Too much airflow can lead to drafts and wasted energy, while too little airflow can make a room feel like a steamer.
The key is to find the right balance.
Keep the room at a comfortable temperature without wasting energy using manual dampers. These dampers allow you to change the airflow according to your needs.
Leave a Clear Path for Return Air
Leaving a clear path for return air ensures the system can circulate air effectively. This prevents hot or cold spots from forming.
Jumper ducts can keep air moving freely and prevent stagnation by removing obstacles.
This can be especially important in areas where ventilation is crucial, such as a laboratory or hospital.
Properly Seal and Test for Leaks
Unsealed ductwork can lead to problems such as:
- Reduced efficiency
- Increased noise levels
- Uneven temperatures
Leak testing is one of the best ways to seal the ductwork.
You have several ways to test for leaks, but the most common method is to use a smoke machine.
As its name implies, it pumps smoke into the ductwork system. The smoke shows where the leaks are.
Use the Right Ductwork Material
Ductwork material also matters. Metal is sturdy and durable and can be easily shaped to fit any space. Fiberglass is also strong and pliable, making it ideal for a tight seal.
Both metal and fiberglass are non-porous. These materials won’t absorb moisture or promote mold growth.
As a result, they are the only materials that can provide the quality and performance required for proper ductwork.
Use Proper Sizing
Using the correct size of ductwork is essential to ensure efficiency and effectiveness.
The size of a duct determines how much air it can push through. If the duct is too small, the system won’t be able to circulate air properly.
If the duct is too large, air will be wasted, and energy bills will go up.
The best way to ensure you use the correct size of ductwork is to consult an HVAC specialist. This way, you’ll be able to maximize the jumper duct’s functions.
You shouldn’t do your own ductwork. There are a lot of calculations that go into figuring out the correct size for the system. If you add on to your existing ductwork yourself, you run the risk of overloading your HVAC equipment.