Ducting tubes move air that has been heated, ventilated, and cooled (HVAC) systems all over a building. When things aren't built or installed correctly, the consequences can be costly and even dangerous to your health. Poor indoor air quality (IAQ) can happen if ducts leak. For example: The EPA and its Science Advisory Board (SAB) keep ranking indoor air pollution as one of the top five environmental threats to public health in comparison risk studies that they've done in the last few years. In addition to IAQ issues, improperly installed ducts can waste energy, wear out the HVAC system, and make people more uncomfortable in the building.

Return, supply, and exhaust air-tansfer systems are all part of ducting systems.

Return: Sends air to the HVAC system to make the air better.

Supply: Makes sure that the conditioned air is spread out all over the building.

Exhaust: Allows air to get into the system.

Supply, return, and exhaust ducts have both common and product-specific things to think about when installing them. Misunderstanding or not paying attention to codes, standards, and manufacturer specifications can cause a lot of problems with duct air flow. These codes, standards, and manufacturer specifications apply to how ducts are integrated into the heating and air-conditioning systems. The goal of this article is to teach you about and help you avoid some of the most common design and field installation mistakes our inspectors see while they're out in the field. These are:

  1. It makes tight bends and crimps to get to component connections.
  2. The length of the duct is too long.
  3. Tightening and sealing the ducts where they connect to other parts.

 Changes in duct size or direction.

It's only two things in your ducts that are making your furnace or air handler have trouble. Reduce the amount of air that comes out of the blower or use more electricity, depending on the type of blower. There is less air coming into the rooms. They can also be cut down, but not eliminated.

Maybe you think it's flex duct that isn't pulled tight, or that it doesn't have rigid elbows, or even the dreaded ductopus. That's why we need to go back even more. Our goal is to find out what caused this. This is very simple physics that I'm talking about. This picture, which looks through a piece of flaccid Flex duct liner, might help you figure out what's going on.


A lot of friction is the first thing that slows down air flow. Air that moves through a duct loses energy when it rubs against the inside of the duct, so it doesn't move as quickly. It takes longer to move. When it's not being used, its pressure goes down. People do more of those things if it rubs a lot. A busy sidewalk with your shoulder against the buildings is like this:

Friction can be caused by things like what kind of duct material it's made of (how it was made), how dirty it is, and how fast the air is moving. When air moves through that duct, there's going to be a lot of friction. Even though you can't see it very well, you can figure out that there will be a lot of friction. A piece of rigid metal duct would make the surface smoother.


Turbulence is also a major reason for less air flow. This one is when the air rubs against itself. Turbulence in ducts is mostly caused by turning the air around, which makes it move faster. Make sure the type of fitting you use to send air through a 90° turn makes a big difference.

There is a lot of air coming in smoothly through both of the 90° elbows. In this case, the water is moving in a layer. When it turns, however, the air in the elbow with the curved inside edge (the throat) makes less turbulence. The elbow with the square throat makes more noise. The fittings you choose can make or break your project.

Friction rates and pressure drops

As previously stated, the outcome of friction and turbulence is a drop in pressure. A supply duct moves air, and the fan behind it pushes it along, making the air move even faster. However, the more it moves down the duct, the more friction and turbulence make the pressure lessen, so it gets less. That's true for good duct systems as well as for bad ones.

Both friction and turbulence are included in the friction rates given for different types of ducts and fittings, so you know how much friction there is. When you see the word "rate," you know that the friction rate doesn't tell the whole story. You have to figure out what the whole pressure drop is by putting it together with something else.

There are a lot of things to keep in mind when you design and build ducts. Whether or not a duct system does what it's supposed to or not depends a lot on friction and turbulence, which are two things that happen when things move quickly. We know how much this is. If you don't use Manual D or a ductulator or some other method that can measure these effects, you may end up with a system that no amount of commissioning can fix, even if you do everything right.

Some Do’s & Don’ts of a ducting:

People use flexible ducting to move heated or cooled air from their homes to fans, grilles, or diffusers.  It's great because it's cheap and easy to move around in small places. The installation of your ducting system has a big impact on how well your ventilation works. There are some things you should do and things you should not do when it comes to your ducting.

This list will help you keep your airflow efficient and powerful.

1. Less is more

Friction and air flow don't go together. When flexible duct is cut with extra length to spare, the air has to travel further than it should and it's exposed to a lot more of the duct surface area, which makes it more likely to get stuck. In order to cut your flexible duct correctly, you will need to measure it a few extra times. The airflow will be much smoother and more efficient because of this.

2. Don't be lazy

There is less airflow when there is a lot of space in the ducts. Bends are made when the duct is too loose. All of the wire ribs aren't stretched tight, which makes it hard for air to flow through. It doesn't matter where you are. Make sure that your flexible duct is stretched all the way out. Installing ductwork in a room can be time-consuming. Make sure there aren't any places where the ductwork can slack, like over a loft beam, before you start.

3. Stay away from the squeeze.

Sharp bends and turns in flexible ducting slow down the airflow. The more twists and kinks there are in the line, the less airflow you get through. There should be no sharp turns when possible. It's not always possible to avoid bends when you're ducting something through a structure. If so, make sure that the radius of any turns you make is at least the same size as the diameter of the duct.

4. Securing the spigot

The wrong way to attach the duct to a fan spigot can slow down air flow. Always pick the right size duct for your fan spigot so that the diameters are the same. For example, if your fan spigot is 150mm in diameter, you should use the 150mm duct to connect it to the fan. Always slip the duct over the spigot and tape or clamp it in place to make sure the airflow is as good as possible.

It's important to follow these steps when installing ducting in your home to make sure the air doesn't get stuck and moves smoothly. Keep an eye out on our blog for more tips and tricks about how to keep your ventilation at its best. Drop us a line on social media to find out more about anything you want to know about. Get in touch with us right away if you think your ventilation system isn't working as well as it should be.


There are important parts of your ventilation system that direct airflow to where it needs to go, whether you are ventilating an entire grow tent or your whole house. Ducting is one of these important parts of your system. Without ducting, your fan is wasting energy because the air it blows back into the room you're ventilating would come back into the room. Ducting, even though it's important, makes your fan work harder to move stale air. Each fitting also makes your fan less efficient. It's less efficient to use duct tubes because of two things. Once you know what's going on, you can take steps to lessen the effect.



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