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Duct Transition

  • Different kinds of Duct Transitions available
  • Thousands of projects experiences
  • Custom service and setting-up team to your site

Biyang Duct Transition, also called Duct Connector is a critical and indispensable part of HVAC ductwork.  It connects the different sizes of ducting, different parts of facilities, and different materials of ventilation components together to ensure the smooth and steady air flow.

Biyang Duct Transition helps the smooth connection between the main duct and branch duct, such as the T Duct Transition, Y Duct Transition, Reducer and so on in the round ductwork system.  It helps fresh air flow from the main duct to smaller ducts when for air distribution.

It also helps get air to extractor duct and exhaust duct.  Biyang Duct Transition also helps ensure the air to reach the right locations or spots, such as getting fresh air from the blower to the Supply Air Diffuser, or exhaust air from the extractor to Exhaust Air Diffuser.

As a leading Duct Fittings supplier, Biyang has all kinds of Duct Transitions and Connectors.  The main product of Biyang Duct Transition is Sheet Metal Transition which is very important in the HVAC ductwork transitions.

This solves your problems of rectangular duct transition, rectangular to round duct transition, or round to rectangular duct transition.  The popular item is like 8 inch round to rectangular transition, 10 inches round to rectangular duct transition and so on.

In addition, with our laser cutting machine, stamping machine and bending machine, it is very easy for us to custom your own Duct Transition based on Sheet Metal Transition at a relatively cheap price.

Biyang Duct Transition also covers Flexible Duct Transition, also named Flexible Duct Connector.  This is made of galvanized steel sheet on both sides with different fabric cloth, including canvas, polyester, and glass fiber with silicon coating.

You can make your own Duct Transition of different shapes based on our Flexible Duct Transition.  Besides the HVAC Duct Transitions, Biyang also customs your own Duct Transitions, such as the clothes dryer transition duct, round duct transition, square to round duct takeoff and so on.

As long as you can share with us about your problem or project, Biyang will always give you a good solution.  Welcome to contact Biyang to custom your own Duct Transition.

ProductDuct Transition
MaterialGalvanized steel, stainless steel

Duct Transition: The Ultimate FAQ Guide

What is Duct Transition?

Duct transitions help in connecting the duct trunks and pipes of your home’s HVAC system.

The connection of the ductwork needs to conform to the shape of your house to ensure the efficient working of the HVAC system.

Duct transition

Duct transition

The duct transition can be cleats, turning vanes, take offs, and other specially designed connectors and can as well end with angled boots.

These components function together to form pathways across your home that blow in pleasant air into your living spaces.

Each of the many duct transitions brings with it a certain level of restriction, which contributes to the Total Equivalent Duct Length (TEL) of the duct system.

The right duct transition minimizes restriction and aids to balance airflow.

How Do You Convert Rectangular Duct to Round Ducts?

For you to convert a rectangular duct to a round duct, you will first have to calculate the equivalent diameter of the round duct.

Rectangle duct to round duct

 Rectangle duct to round duct

The equivalent diameter is the diameter of a round duct that for equal airflow provides similar resistance or pressure loss as an equivalent rectangular duct.

A round duct leads to lower pressure drops and reduced fan horsepower necessary to move the air, as a result, smaller equipment.

You can calculate a rectangular duct equivalent diameter as (Huebscher)

de = 1.30 (a b)0.625 / (a + b)0.25


a= length of major or minor side (mm, inches)

b= length of minor or major side (mm, inches)

de = equivalent diameter (mm, inches)

The formula is generic and you can use any unit.

Example – Equivalent Diameter

You can calculate the equivalent diameter of a rectangular duct measuring 500 mm x 300 mm as

de = 1.30 ((300 mm) (500 mm))0.625 / ((300 mm) + (500 mm))0.25

= 420 mm

There are also Apps available for converting Rectangular-to-round ducts, both for Android and Apple systems.

As you enter dimensions, the app calculates automatically the equivalent round diameter.

You can also learn more from: Duct Sizing Charts and Tables.

Is Round Duct Work Better than Rectangular Duct Work?

Both duct types come with advantages and disadvantages, and each finds use where one is superior to the other.

However, around duct is more efficient than rectangular ductwork in accomplishing the same work.

It as well has a smaller cross-sectional area and has smaller extent of duct wall subjected to moving air.

An 18 inches diameter round duct, for instance, has a similar air-carrying capacity as a 26 inches wide and 11 inches high rectangular duct.

The round duct has a perimeter of 4.7 feet and cross-sectional area of 254.5 square inches, whereas the rectangular duct has a perimeter of 6.2 feet and an area of 286 square inches.

Therefore, the cost of the rectangular duct should be proportionately high, since it has 32% more metal in it.

Round spiral duct

Round spiral duct

One of the greatest disadvantages of round ductwork is its height.

You cannot install an 18 inches duct, for instance, if you have 14 inches net clear height of a furred space over suspended ceiling.

Nonetheless, its corresponding 26 inches wide by 11 inches high rectangular ductwork will position in the space easily.

Rectangle duct

 Rectangle duct

What are Duct Transitions Used For?

Duct transitions are instrumental in connecting the duct trunks and pipes in your HVAC system.

Almost every duct run requires transitions to alter the size or shape of the ductwork.

Every duct system comprises of numerous transitions, from rectangular to round and from trunk lines to branch lines.

Duct transitions also join the plenum to the primary supply trunks and the primary return air trunk to the return airdrop.

Duct network

Duct network

How do Duct Reducing Offset Compare to Duct Transition?

Ductwork reducer offset fall in the category of duct transitions, though it plays a specific role in the ductwork system.

They are a common component of a HVAC duct system.

They often find application when avoiding obstructions, either structural, for instance, columns, beams, etc.

Or, if avoiding other mechanical services comprising of electrical installations or pipework.

You may use them to readjust a duct run by reducing its size to allow it to go through a narrow space or to enable a final attachment with HVAC device.

Sometimes you will have them produced as an “additional” i.e. a variant to the original ductwork design.

It is because of oversight during the process of design, or unforeseen obstacle at the job site.

What are the Benefits of Duct Transition in HVAC Systems?

Duct transition system

 Duct transition system – Photo courtesy: CED

Duct Transition is an essential and indispensable component of HVAC ductwork.

It connects the various sizes of ducting, different facilities parts, and varying materials of ventilation parts together to make sure there is a smooth and steady flow of air.

These HVAC duct fittings also help in the smooth coupling between the main duct and the branch duct.

These may include reducer, Y duct transition, and T duct transition among other fittings in the round ductwork system.

This is instrumental in ensuring the flow of fresh air from the main duct to branch ducts during air distribution.

Duct transition equally helps to guide air to the extractor and exhaust ducts.

In addition, they as well ensure that air reaches the correct spots or locations.

For instance, guiding fresh air to the supply air diffuser from the blower, or exhaust air to the exhaust air diffuser from the extractor.

How will Duct Transition Affect Air Flow Rate?

As air flows from a larger to a smaller duct, it will register an increase in velocity.

On the other hand, when it flows from a smaller to a larger duct, it will register a decrease in velocity.

In both scenarios, the airflow rate – the quantity of air moving across the duct, in cubic feet per minute, remains the same.

What Types of HVAC Duct Transition Systems are Available?


There are several HVAC duct transitions you can use to connect the duct trunks and pipes.

The common transitions used in ductwork include take offs, specialized connectors, cleats, and boots.

· Take Off

At times, the design of HVAC ductwork system may require that the primary duct feeds air into branch ducts.

Fittings known as take offs enable the diversion of the correct proportion of airflow from the main duct into each branch.

They come in various shapes consisting of round, rectangular and oval.

· Connectors

Connectors mainly play the role of strengthening fittings, as well as for joining two ducts.

The most common types are:

i. Standing “S” Cleat paired with Drive Cleats

ii. Flat “S” Cleat paired with Drive Cleats

iii. Pocket Lock (or Cliprol)

iv. Bar or Angle Cleat paired with Drive Cleats

The type of application and the strength required determines the type of connector you will use.

However, the usage is not fixed and differs depending on the geographical area or location where you will be performing the work.

· Cleats

Cleats are popular ductwork fittings for essential in the connection of air ducts.

This is because they are stable, easy to use and provide an outstanding finish to the flange connection.

They are the first option whenever there is limited space during duct fitting.

This is because cleats require less space for assembly in comparison to G-clamps.

When using cleats as duct transition, you should cut them in lengths 70-100mm and use them in distances not exceeding 300mm.

Generally, the distance should not exceed 200mm.

· Boots

Boots are fittings that are rectangular on one end and circular on the other, which enable it to connect to ductwork round pipe.

Boot transition is framed into the ceiling or floor, with the rectangular section facing the room.

There are different types of boots available in the market, with the three most common being straight, angle and end boot duct transitions.

The angled boot offers a 90-degree angle, which enables the ductwork to switch directions from horizontal to vertical.

An end boot transition is utilized with terminations. Simply put, it transforms the ductwork into a vent.

A straight boot duct transition finds use when the duct run is already straight, where you use it to convert the ductwork into a vent.

How Does T Duct Transition Compare to Y Duct Transition?

· Y Duct Transition

Also called reducing laterals or wye joints. Find application in HVAC ductwork systems for a transition from a single pipe to two pipes.

In addition, there is also 45-Degree Wye Saddle important for splicing into an existing line of round pipe of equivalent or larger diameter.

It commonly find use in supply air duct runs.

T duct transition

T duct transition – Photo courtesy: Perfect Home Designs

T Duct Transition

Also referred to as Tee, T duct transition is appropriate for branching a main duct run or a branch ductwork line with a 90-degree angle.

There is also T saddle duct transition which is essential in splicing into an existing line of round pipe of equivalent or larger diameter.

It is ideal for 90-degree angle branch.

 Y duct transition

 Y duct transition

Is Duct Reducer Same as Duct Transition?

Duct Reducers are the ductwork fitting in HVAC systems that you utilize when you want to switch from one duct size to another.

They are appropriate sheet metal fittings for sustaining maximum airflow across your system while switching to the required duct size to fit into tighter spaces.

HVAC technicians commonly utilize a reducer on a duct line’s main trunk to establish a smooth transition from the duct of larger size to a smaller one.

A duct reducer helps in maintaining a higher velocity airflow, implying that the air will go to farther areas of your home.



From the explanation above, we realize that duct reducer is a specific type of duct transition.

It purposely helps in ductwork transition from larger to a smaller pipe.

Are Flexible Duct Connector and Flexible Duct Transition the Same?

Flexible duct connector, also referred to as flexible duct transition is an essential component of a ductwork system.

It is a special kind of HVAC duct transition critical in making fabric compensators.

These compensators are instrumental in avoiding vibrations transmission in rectangular or spiral ductwork and appropriate for acoustic decoupling.

Therefore, flexible connectors usually play the role of a connecting fitting between ventilation ducts and devices or fans.

Flexible duct connector

Flexible duct connector

Flexible duct connectors comprise of a fabric, for example, glass fiber with PU coating or polyester with PVC coating, which you attach to the sheet metal on both ends.

The material used for making the sheet metal can either be stainless steel or galvanized steel.

What is the Best Material for Duct Transition Construction?

Duct transitions come in a myriad of materials and sizes and can either be rectangular or cylindrical.

In most cases, you will find them insulated.

Materials used for the construction of duct transitions are hardy, durable, and reliable.

The most popular types of rigid ductwork are Sheet metal duct transitions.

Aluminum and galvanized steel are the most popular materials for the construction of sheet metal duct transitions.

Specifically, aluminum is comparatively light and facilitates ease in installation.

In addition, they are as well the least probably to host hazardous molds or growths since their surfaces are non-porous.

Generally, sheet metal is the most secure and effective material for the construction of duct transitions.

How do You Minimize Restriction and Balance Airflow in Duct Transition System?

Poor installation, undersized ducts, crushed, kinked, or damaged ducts are typically the causes of restriction in duct transition.

Repairing some restrictions may be as simple by just opening a closed damper.

It is this restriction that brings about airflow imbalance within the ductwork system.

Balancing a HVAC duct transition system means managing this restriction to lead air in the appropriate direction.

Here are some of the common methods of balancing airflow in a duct transition system:

Air flow in duct system

 Air flow in duct system – Photo courtesy: CIBSE Journal

Test and Balancing

You can seek the services of a test and balancing expert, or a professional HVAC technician to determine the airflow in your ductwork.

When it is a simple airflow issue, they can rectify it by shifting balancing dampers into different positions to equalize the flow of air to each space.

They conduct this by establishing the airflow at every duct.

Then changing damper positions manually to reduce or raise the static pressure until a similar quantity of air flows to every room.

The technicians can as well detect leaks in duct transitions that are negatively impacting on the pressure.

Increasing Fan Speed

Another mechanism through which your HVAC expert may balance airflow in the duct transition system is to raise the speed of the fan of your unit.

In case you have balanced the ductwork, yet it is not attaining the correct airflow, you can adjust the motor speed of your unit to boost the airflow per minute to every room.

The raised speed will thrust more air across the duct transitions, increasing static pressure and the quantity of CFMs pumped to every area of the home.

Resizing Ducts

When balancing dampers and raising the speed of fan does not rectify the air balance problem in your HVAC system, you may need to resize the duct transitions.

This will resolve the issue indefinitely, though maybe more costly than just balancing your duct transition system.

This is a familiar problem in houses that have had non-identical size HVAC units fitted, or have new add-ons installed, or renovated rooms.

If this is the case, you should consult a seasoned HVAC expert to carry out load calculations, to establish the correct sizing of your ductwork transitions.

The finding will help them establish where you may need to replace or alter the duct transition system in your home.

· Sealing Leaking Ducts

When your duct transition system is losing pressure, it could be because of leaks.

Actually, the average home HVAC duct system loses around 20-30 percent of its air due to leaks brought about by aging tape and sealant.

A certified HVAC expert can locate the leaks and secure them, reinstating the pressure in the duct transition system.

Are there Standard Sizes of Duct Transition Systems?

Duct transition system

Duct transition system

The size of ducts and duct transitions system depends on the size of the HVAC system installation design as well as cooling or heating space aspects.

Local building and residential code stipulations also influence sizing in several installation scenarios.

Square or Rectangular ducting duct transitions come in standard sizes varying from 3-by-7 inches to 35-by-40 inches.

Sizing is dependent on airflow requirements per cubic foot per minute, together with velocity.

Round ducting and duct transitions come in standard sizes varying from 4.9 inches in diameter to just above 41 inches in diameter.

Sizing also depends on airflow requirements per cubic foot per minute, as well as velocity.

How do You Convert Round Duct to Rectangular Duct?

In some instances, space availability may compel you to apply rectangular ducting.

There are duct transitions in the market that can enable you to switch from round to rectangular duct.

However, before you purchase one, ensure you measure the area of cross-section of both types of the duct.

Duct transition from round to rectangle

 Duct transition from round to rectangle

Step 1

Take measurement of the round duct diameter, which is the broadest length from one end of a circle to the other. For instance, 8 inches.

Step 2

Get the radius of the cross-section of the circular duct by dividing the diameter by 2.

In the Step 1 example, 8/2 = 4 inches.

Step 3

Get the square of the radius by multiplying the radius by itself. For example, 4 x 4 = 16.

Step 4

Calculate the area of the circular duct in square inches by multiplying the square of the radius (step 3) by 3.14 (pi).

For instance, 16 x 3.14 = 50.24 square inches.

Step 5

Choose a square or rectangular duct with the same area as step 4.

You can find this by multiplying the length by the width of the rectangular duct.

For instance, if you find a duct measuring 10 inches by 5 inches, its area will be 50 square inches.

Step 6

Choose a duct transition that will switch between the round-to-rectangular duct sizes from your local building supply shop.

For example, you should mate 8-inch round duct to10-inch by 5-inch rectangular duct since they have equal cross-sectional area.

What other HVAC Duct Fitting does Biyang Provide?

As an experienced and professional HVAC Duct and Duct Fittings manufacturer, Biyang offers a wide range of products in this field.

Among the other duct fittings we provide include:

  • Hose clamp
  • Duct connector
  • Duct insulation sleeve
  • Duct boot
  • Duct splitter
  • Insulation protection shield
  • Flexible duct connector
  • Line set cover

Biyang duct fitting

Biyang duct fitting

How does Biyang Control Quality of Duct Transition?

We manufacture all of our duct transitions in our factory, by our skilled craftsmen.

Our quality control department meticulously inspects the HVAC fittings to guarantee perfection and maximum durability.

Biyang is aware that quality duct transitions are crucial for efficient airflow in home HVAC systems.

Our primary drive is to fabricate and supply our clients with products that reflect superior strength, high tensile strength, low leakage rate, and durability.

Can Biyang Custom HVAC Duct Transition System?

Biyang can customize your duct transition system to meet any installation requirement and provide transitions from one size to another.

We can customize HVAC ductwork transition systems, round duct transition, clothes dryer transition duct, and square to round duct takeoff among others.

Our in house manufacturing plant gives us the freedom and flexibility to custom fabricate any duct system to the unique specific needs and requirements that our customers desire.

Does Biyang Support OEM Duct Transition Businesses?

Yes, Biyang allows for the purchase of their duct transitions on OEM terms.

This allows HVAC system technicians or assemblers to get low cost high-quality duct fittings.

Can Biyang Provide Duct Transition CAD Drawing and Designs?

Yes, Biyang can offer duct transition CAD drawings and designs.

We understand that in most HVAC works, handling of the HVAC duct fittings can be the most difficult task, particularly for renovation projects.

It will be necessary you utilize the exact duct transition for replacement, yet you might not be able to ascertain every detail.

For that matter, Biyang can send over a special technician team to your site to help you solve the problem.

They can assist in measuring every detail and develop the CAD drawings and designs to ensure everything is right.

Why Import Duct Transitions from Biyang?

Biyang has vast experience in managing project orders, custom engineering, and product fabrication.

We have a full product line offering you a one-stop shop.

We boast of over 1000 popular projects experience home and abroad.

We were in charge of all the HVAC ductwork set up at Shanghai Disneyland, National Exhibition and Convention Center and Samen Nuclear Power Station among other projects.

This makes us have a clear mastery of your general HVAC projects and needs.

In addition, our sales team will work round the clock to ensure timely delivery or completion of your products or projects.

Does Biyang Help in Duct Transition Shipping?

Biyang can assist in the arrangement for shipping of your duct transition from China to your destination country.

We have a better understanding of the freight Logistic sector in China, and our experience and network may help you save cost in shipping.

What is Biyang MOQ for Duct Transition Fittings?

You can always request for a free sample of duct transition fittings before placing an order for the product.

However, normally our MOQ for ducting transitions is 500pcs per item.

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