6 Inch Vs 8 Inch Duct

6 Inch Vs 8 Inch Duct : All You Need to Know


The HVAC system in a house is mainly powered by a centralized heating and air conditioning unit, but the ducting in closets and crawlspaces is equally crucial. Various sizes, dimensions, and materials are used to make air ducts.

So, 6 inch vs 8 inch duct?

Keep in mind that the cross-sectional surface of a 6″ duct is only 56% that of an 8″ duct. You are thereby losing half of your capability. That has a significant influence on a hood that needs an 8″ duct. Only choose a hood if you can meet the installation criteria for it. 

If you don’t follow the rules for your hood, you’re asking for problems. It is difficult to determine exactly how much airflow you will want for your specific use. 

Your use of your available range and your expectations will determine how it turns out.

We will talk about this more. Let’s get going!

6 Inch And 8 Inch Duct: Quick Comparison

How much CFM is there in a 6-inch duct? The airflow through a 6×6-inch rectangular duct is 110 CFM. Larger 612-inch ducts have an airflow capacity of 270 CFM. 

CFM increases with duct cross-section size; this much is certain. Airflow of 60 CFM may be handled by the smallest 64 ducts. The largest 4212 ducts, which have a 504 sq inch crosssection. 

It can move more than 3000 CFM of air. So, we have a quick comparison for 6-inch and 8-inch ducts:

Feature6 Inch Duct8 Inch Duct
Airflow75 CFM160 CFM
Temperature Range20°F – 100°F20°F – 160°F
Price Range14$ – 35$25$ – 55$

You should enter Flex duct =.05′′ to get an accurate result when utilizing metal duct calculators.

6 Inch Vs 8 Inch Duct: Detailed Comparison

For usage in HVAC air ducts, the “HVAC Insulated-Flex” hose is an excellent option. These flexible double-ply insulated ducts for use in air conditioning are constructed from PET film. As well as aluminum foil layers. 

Glass wool is used to insulate each flexible HVAC duct. Due to this product’s reasonable pricing, buyers may benefit from it. In comparison to other competing hoses, it is unquestionably a more affordable HVAC ducting alternative. 

Here we have something which may become handy for you:

Product 1
Product 2

It will additionally look beautiful in any environment in which it is used. Here we have discussed some detailed comparisons:

Airflow of Ducts

Adequate air exchange is linked to a safe and healthy work environment. In addition to giving fresh air and removing polluted air from industrial and commercial buildings. Ventilation also removes dust, chemicals, and other particles. 

The technical integrity of the building and people’s health may both be impacted by inadequate air exchange. This actually happens within the structure.

There is inability to supply the human body with an optimal microenvironment. It is due to inadequate ventilation regrettably is inextricably linked with the decline in wellbeing. The Sick Building Condition, whose symptoms include headaches and vertigo, fainting, and exhaustion.

As well as irritation of the mucosal surfaces, in addition to an increased incidence of asthma and allergies. There are respiratory tract infections, that may be brought on by inadequate air exchange.

That is why airflow is a vital factor for any building. Here we have discussed about airflow capacity of both 6 inch and 8 inch duct. Here we have discussed about airflow for both:

6 Inch Duct

6 ich duct can deliver up to 75 CFM. Which is normally preferable for small to medium rooms.

8 Inch Duct

6 inch duct can deliver up to 160 CFM. Which is normally preferable for medium rooms.

You can calculate the pressure loss at a 90-degree curve. With a long radius for a rectangular channel with a width of 200 mm. And a height of 400 mm. 

When the air density is constant, the rate of airflow is 0.6 m3/s.

The Shape of The Ducts

Rectangular duct bends are categorized as either hard or easy. On the axis of the longer side, a hard bend spins. It is while the easier bend spins in the axis of the smaller side.

Nose radius = 100 mm for ducts with a width of up to 300 mm and a short radius bend. Short radius bends with splitters in accordance are required for ducts wider than 300 mm।

Medium radius bends with r/W = 1.0 and long radius bends with r/W = 1.5 are required for all duct widths.

6 Inch Duct

6 inch duct is rectangular in shape. One of the most common and well-liked ducting size. It utilized by a wide range of industries is 6 inch duct. 

6 inch duct serves as the ideal size compromise between rigid. And flexible since it is big enough to move a lot of material but small enough to be manipulated. As well as can be moved around while in use. 

6 inch duct has established itself as a standard for bill of materials and ventilation applications. Because it is small enough to fit in small spaces and confined places. Additionally, because of its six inch diameter.

This kind of flexible ductwork can move a sizable volume of air. And also pollutants at any given moment.

8 Inch Duct

The 8 inch duct is also rectangular in shape. Here, just the unique instance of a rectangular channel with flawlessly reflective drywalls is examined. When the liquid is moving, the example of a piston gripped in the barrier is particularly fascinating. 

The source’s presence does not cause the flow to be perturbed. Only vitro propagation modes must be considered in the far field, as was previously stated. 

The source’s position and shape have no discernible effects on the modes. This statement still applies to sensors, at least roughly. But when the detectors are built into a wall.

They are located within the transition zone, necessitating a more thorough investigation of the issue.

Temperature Range

It is one of the factors before selecting the duct for use. Here we have discussed that:

6 Inch Duct

6 Inch duct can absorb 20°F – 100°F. This is very much acceptable for most of countries.

8 Inch Duct

6 Inch duct can absorb 20°F – 160°F. This is very much acceptable for the middle east countries.

Friction Rate in Design

The most often used method of sizing ducts is designed friction rate. This is why many people believe a 6″ duct produces 100 CFM. Because many slider duct calculators propose a residential setting of.10″ of the water column.

That is why it is such a generally accepted assumption. There is a lot of uncertainty at this point. Since many people think they must apply this design pressure.

On a slider duct calculator, the suggested residential setting is for 100 comparable feet of duct. This represents how much straight duct the duct fitting can replace. One wide way 90° elbow with a rectangular throat.

A circular heel, and no rotating vanes may quickly eat up 100 comparable feet of duct. Consider this: 100 feet of direct would equal one elbow with a rectangular throat.

A round heel, and no turning vanes. Before you know it, you may have more than 500 feet of similar duct. This is depending on how complicated the duct system is. 

This builds up rapidly and often leads to a duct system. That is too small to accommodate the necessary airflow.

Frequently, individuals who choose the side of prudence set their design standards even lower than.10. These people all have the same passion, yet the design numbers they utilize vary greatly. 

From.08 on the supply and.06 on the return to.10 on the supply and.05 on the return.

Final Verdict

We have discussed everything regarding 6 inch vs 8 inch duct. Now you have to choose the one according to your need. 

Because the capacity is not the same for both of the ducts. We hope that the comparison will help you to choose the right one.


Are Larger Ducts Preferable?

Air will flow in the direction of least resistance when the duct size is restricted. There will be greater resistance and less air flow. Because they all run in parallel, the 6″ duct would have a larger flow than an 8″ duct. A decrease like that would make noise worse.

Do Ducts That Are Smaller Cause Pressure To Rising?

To calculate pressure losses/gains across a system for parallel sections. It always utilizes the section with the greatest pressure loss/gain. By raising the flow rate or reducing the duct size. Adjusting the branches with the pressure drop loss/gain to raise the pressure drop to that of the upper branch.

Is a Square or a Circular Duct Better?

Round metal ductwork reduces the likelihood of dirt and germs forming in the duct. Since it has less contact area, no angles, and improved airflow.

Final Words

We hope that now you have enough knowledge regarding 6 inch vs 8 inch duct. Hope this knowledge will help you in your needs. 

We will talk shortly. Have a great day!

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