How to Install Air Conditioning and Heating Ducts in Your Home or Office eBay

How to Install Air Conditioning and Heating Ducts in Your Home or Office eBay

How to Install Air Conditioning and Heating Ducts in Your Home or Office

The largest and least glamorous part of any home or office HVAC system is the ductwork. Without ducts to carry the heated and cooled air throughout the building, these systems can only heat or cool one room. With properly planned and installed ductwork, however, one HVAC air handling unit is sufficient to keep the temperature of a large house comfortable.

Obviously, the size of the air handling unit and the air conditioning condenser are important. They must be sized appropriately to provide enough airflow for the air volume of the home or office. Thus, a building with high ceilings needs a more powerful air handling unit and a larger condenser than one with normal 8-foot ceilings. In addition to the size of the HVAC system, this guide focuses on designing and installing the ductwork. Read on to learn how to install air conditioning and heating ducts in your home or office.

Types of Ductwork

There are three basic types of ductwork used for homes and offices, with a fourth method that can be done for parts of homes, without any ductwork at all. The three types are sheet metal ducts, duct board, and flexible ducts. Metal ducts are traditional, but the most expensive, often needing to be custom fabricated to match the area. They are also not insulated, which causes them to lose heat into attics, ceilings, and crawl spaces. For this reason, duct board has largely replaced metal ducts.

Duct board is an aluminum foil-coated fiberglass insulation panel. It provides several advantages over metal, while being less expensive to install. The ductwork can be easily cut to size with a utility knife and shaped to meet the needs of the building, and is insulated.

Flexible ducts are used in conjunction with both of the other types of ductwork, predominantly to go from the main duct to individual heating and cooling registers. This makes the installation of these much faster and easier, reducing the overall installation time.

The fourth method, which is used only in homes, is to use the space in the walls or ceilings for ducts. By capping off a section between two studs with aluminum flashing, an instant duct is made. The same thing can be done in the floor joists. While quick and easy, this method depends on the framing of the house running in the right direction to be useful in this manner.

The Return Air Plenum

When laying out a ductwork plan, it is important to consider the return air plenum. The air handling unit pumps a large amount of air through the home or office. It needs a constant supply of air to heat and cool so that the air can be returned back to the living spaces.

The return air plenum needs to be located in a place where it is as far from the HVAC registers as is practical. It also needs to be located in a place where it is close to the air handling unit so that the unit does not have to work to pull the air into it. The air filter is located at the entrance to the return air plenum, and the thermostat is usually located close to it.

Choosing an Installation Location

Most ductwork is installed in either the basement or attic of a home. For businesses and offices, it is installed above the suspended ceiling. This allows it to be installed in areas which are not occupied and are out of the way of traffic. It is usually best to install the ductwork once the building is framed in, but before the installation of drywall. Often, the ductwork is installed at the same time as rough electrical work.

If ductwork is installed in the basement, floor registers are usually used. If it is installed in the attic or above a suspended ceiling, ceiling registers are normally used. Each system has its own advantages. For more efficient cooling, an attic installation is better. For more efficient heating, a basement installation is better.

Heat Registers

Heat registers are the vents which allow the air from the HVAC system to enter into the living and working spaces. A grille is provided to help prevent things from falling into these vents, make the opening more attractive, and keep rodents out of the system.

Designing an HVAC Ductwork System

When designing a ductwork system, size is everything. The starting size has to be the outlet size of the air handling system. While there are many sizes available, the most common size used for homes today is 20 inches square. This provides 400 square inches of air movement. This number is important, as that quantity of air must be split up and sent to the various rooms which are to be heated and cooled.

For simplicity’s sake, let us use the example of a house where all the rooms are roughly the same size. If this house has eight rooms, then each room can receive 12.5 percent of that total air volume, or an equivalent to what 50 square inches of the duct is carrying. This would necessitate a 5-inch by 10-inch heat register. Of course, most homes have larger and smaller rooms, meaning that the sizes of the registers and the branch ducts leading to them need to be adjusted accordingly.

There are several ways of designing a ductwork system, including a perimeter loop, a radial duct system, and a trunk system. The trunk system is by far the most common, as it requires the least amount of materials and labor to install. A trunk system is similar to a tree trunk, with branches coming off it. As the trunk gets farther from the roots (the air handling unit), the trunk becomes smaller, with a portion of the air going off in branch ducts, to individual rooms and registers.

This stepping of duct size is a very important part of designing an effective ductwork system that will provide heating and cooling to the entire building. If the trunk is not stepped, then the system cannot be balanced.

Sizing of these steps is not random, but rather, it is calculated. We started out with 400 square inches of duct cross-section. Branching off the duct to two rooms might require a duct of 80 square inches (for two 4-inch x 10-inch registers). Thus, the trunk duct would need to be reduced to 230 square inches (16 inches x 20 inches) immediately after the branch duct is connected to the trunk.

In this way, an appropriate amount of the air is forced to go down the branch duct, while the majority of the air continues down the trunk. With the entire system designed in this manner, available airflow to each room remains the same.

Another thing to avoid when designing the ductwork system is bends. While some bends are necessary, they all cause restrictions which reduce airflow. If a 90-degree bend is needed, it is better to use two 45-degree bends, if space allows. This makes it easier for the air to continue flowing, without creating any backpressure.

Installing Ductwork

When installing ductwork, it is best to work from the air handling unit outward, installing the trunk with all the necessary transitions from one size to the next. When using insulated duct board for the ducts, they are attached together with a system of S-cleats and drives. The S-cleats are used to connect the tops and bottoms of the ducts together. Each piece of ductwork fits into a separate slot. Then the drives are attached to the sides, bending them over on themselves to lock them into place. An end cap needs to be installed to the end of the trunk, unless the trunk splits to form branch ducts.

If metal ducts are used, they are designed to be connected together by a slip fitting. Short drill-point sheet metal screws are used to connect adjacent pieces together mechanically. The same type of connector is used for branch ducts, as for duct boards and flexible ducting. Trunks that are installed above a suspended ceiling need to be supported a minimum of once every 8 feet.

Holes are cut into the sides of the trunk for branch ducts. These can either have a rectangular or round cross-section. If the branch duct needs to go to several registers or needs to split into two branches, then a rectangular section is normally used. If flexible ductwork is used as branch ducts, it is always round.

The holes in the trunk need to be sized for the branch. A metal joining collar is used, which slips into the hole and is crimped to the inside and outside of the trunk by bending tabs. The duct slips over this joiner and is attached.

How to Install Air Conditioning and Heating Ducts in Your Home or Office eBay

Flexible ducts are installed the same way as branch ducts, whether the flexible duct is attached to the trunk or to a branch duct. It is very common to use a flexible duct as the termination duct, as it is easy to install and does not need to be fitted exactly to the register box. Flexible ducts are held in place by the use of large plastic wire ties and then sealed with duct tape.

The register box is an insulated metal box that is shaped to receive the duct or flexible duct on one end and the register at the other end. It has a flange at the register end, allowing it to be connected to studs and drywall, and to have the register attached to it.

Every joint in the ductwork needs to be sealed with duct tape. This is the original use of the infamous duct tape, which handymen now use for everything from HVAC ducts to repairing rips in their blue jeans. Alternatively, many professionals now use aluminum foil tape for duct work; this type of tape provides a better seal and is less susceptible to heat damage.

The final step in a duct installation project is to install the registers. This is not done until the home or office is almost completed. At a minimum, the drywall needs to be finished, along with the texturing and painting. If the registers are going to be mounted in the floor, the floor covering should be installed before them.

Buying Air Conditioning and Heating Ducts on eBay

eBay is a great source for all types of building supplies, including HVAC ducts. In many cases, the sellers are trying to dispose of leftover parts from a project they have completed, so they are willing to sell their parts much cheaper than retail. Since ductwork from different manufacturers is totally compatible, there is no need to seek out only listings which supply enough material to do an entire project.

Ductwork can be found listed in more than one category on eBay because it is used in homes and businesses alike. Often, the same size parts are used in both homes and offices, although some larger sizes are used in industry and not used in homes. Since ductwork is found in more than one part of eBay, the easiest way to find ductwork on eBay is to do a keyword search for HVAC duct . Simply type these words into the main search bar on the eBay homepage and hit Enter. This will find all parts, regardless of where on eBay they are listed.

Shipping of ductwork is inexpensive, as most shippers charge by weight. Even metal ducts are extremely lightweight for their size, making it easy and inexpensive to buy ducts on eBay and have them shipped to your home or office.


Installing the heating and air conditioning ducts into a home or office is the most labor-intensive part of installing the system. Therefore, doing this work oneself, rather than hiring a contractor, is a great way to save on labor costs.

The actual installation of the ducts is extremely simple, especially now that most installations use insulated duct board, rather than metal ducts. However, the challenging part is designing the system so that it provides the maximum possible balanced airflow. Balanced airflow refers to the same amount of heated or cooled air being available to all rooms in the building.

The secret to balanced airflow is to properly size the trunk and branch ducts to match the need. The starting dimension is determined by the supply air outlet on the air handling unit. As the trunk continues and branch ducts come off of it, the trunk needs to get smaller by the same amount of square inches of cross-section used for the branch ducts.

Proper sealing of the entire system with duct tape or aluminum foil tape is critical to get the best possible efficiency out of the system, as any joint holes that are not fully sealed allow a part of the total air to escape into areas where it is not used.

Using the information in this guide, you can purchase and install HVAC ductwork with ease and be relaxing in your temperature-controlled home or office in no time.

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