How to Choose Ductwork for Your Home

Key Points Covered

How to understand your HVAC system type: Common options include split systems, hybrid (dual-fuel) systems, packaged systems and ductless mini-split systems, each offering different heating and cooling configurations.
How to choose a duct layout that fits your home: Duct design should support your home’s size and layout, ensuring balanced airflow throughout the space.
The main types of duct components: These include trunk ducts, branch ducts, takeoffs and starting collars.
How to choose the correct duct sizes: The right choice will deliver maximum airflow efficiency.

Types of Duct Systems

Split System: This system involves a combination of two different types of HVAC units, typically a heating and a cooling unit. The most common example of a split system would be a gas furnace paired with an air conditioner (A/C) or a heat pump.

Hybrid System: This advanced version of a split system uses smart technology to switch between electric and gas heating for maximum efficiency.

Package System: This all-in-one system provides cooling and heating within a single unit and is installed outside.

Ductless System: Sometimes referred to as a ductless mini split, this system conditions the air for one room or several rooms and doesn’t use any ductwork.

HVAC Ductwork Design

Here’s an example of how the most frequently used duct system components are laid out in a residential HVAC system. When considering how to install ductwork, you’ll need to select a duct layout design that supports the size of your home.

An illustration of a residential H V A C system.

Trunks and Branches

In an HVAC system, a trunk is a large, main duct — usually located in a ceiling or crawlspace — that carries heated or cooled air away from the furnace or A/C unit. In certain configurations, these ducts can run nearly the entire length of a home. Trunk ducts have an endcap at the end of the run.

Branch ducts split the airflow from the main trunk duct and divert it to individual areas or rooms of a home. Think of the main trunk duct as a tree trunk and the branch ducts as the limbs that extend from it.

Starting Collars and Takeoffs

A galvanized duct takeoff with a starting collar installed in a ceiling.

A duct takeoff is the fitting that connects a duct branch to the main trunk. A starting collar is another type of fitting needed to connect a duct component with a flat surface — for example, a duct board — to another type of duct pipe with a round opening. The main purpose of these components is to help direct the air into the duct branches while ensuring a tight seal.

In-Wall Ducts

A galvanized steel wall duct attached to two wooden wall studs.

As the name implies, in-wall ducts — sometimes referred to as wall stack ducts — are installed inside walls or between wall studs. Airflow is routed from a main trunk through branches and into wall ducts.

Register Boxes

A galvanized register box installed in a wooden floor.

Once heated or cooled air leaves in-wall ducts, it typically travels into register boxes and then into the various rooms of a home. The purpose of these final ductwork components is to allow you to control airflow into the room with dampers, which you can open or close. Register boxes are often installed near structures through which cold or hot air can escape — such as doors or windows — to help maintain optimal room temperature.

Tip

See How to Find the Best Vent Covers for Your Home and our Decorative Floor Register Buying Guide for help with choosing the finishing touches.

Transitions and Connectors

A steel duct elbow installed in a ceiling.

Duct transitions and connectors are fittings used to create turns or bends in ductwork to accommodate structures like walls, ceilings and floors. These duct components help installers easily design a duct system to fit virtually any type of home layout.

Return Air Ducts

Return air ducts, or return vents, pull air from a room in your home and deliver it back to the A/C or furnace where it can be filtered and processed again. Although each room of your home doesn’t necessarily require a return vent, your home should have multiple vents located in certain areas, particularly in bedrooms. The easiest way to tell if a vent is a return vent is to hold a piece of paper over it. If the vent sucks the paper toward it, it’s a return vent. In addition, return air vents are typically larger than register vents, and you can’t adjust their air flow.

HVAC Duct Sizes

For an HVAC system to run smoothly and effectively, it’s important to choose the right duct sizes for all components. To calculate this, professionals use a complex formula. But, in general, here are some of the measurements an HVAC professional will consider:

Square Footage: Measuring your home’s square footage will allow a technician to understand the total area that an HVAC system needs to cover. For rooms that are oddly shaped, you can calculate square footage by dividing the area into rectangular portions and adding up the total measurements for the room.
Friction Loss Rate: To simplify, friction loss rate measures pressure drop per unit length of duct due to air resistance. The length, width and number of the various duct branches and components that are fed from the main trunk can all affect this metric.
Cubic Feet per Minute Formula: 1 ton of cooling = approximately 400 CFM. Although this is the basic formula, technicians today will also consider other important factors that can affect the performance of your HVAC system, so most will use a special program or other calculating tool.

Ready to Get Started?

With the right HVAC components from Lowe’s, keeping your system running smoothly and efficiently is simple. Whether you’re upgrading existing ductwork or planning a new installation, having quality parts makes a difference in performance and comfort. Explore some of the most popular categories customers rely on for their home improvement projects.