What size flex duct should i use

Once the appropriate duct diameter is determined, establish the duct layout in coordination with the framing plan. Ensure that adequate space is allowed for all trunk and branch duct runs. Figure 2. R-6 flex duct has 2 inches of insulation around the inner liner. If the required duct run is a inch round, the exterior radius will be about 16 inches. At a minimum, a 16xinch duct chase or opening would be required along the full length of the duct. Figure 3. Ensure that the air handler location does not conflict with duct routing.

Figure 4. The height and width of a dropped soffit used to house ductwork should be the duct diameter plus the thickness of the insulation to prevent compression of the duct.

If room is tight and there is fear of compressing the flex duct when making a degree turn, use a metal elbow. Figure 5. Use a metal duct elbow instead of flex duct at boot connections to prevent compressions. Coordinate with the framer, plumber, and electrician for effective duct installation with adequate space. Ensuring Success. Right and Wrong Images. View Image Download. Framing allowed duct work to be properly installed without compression. Recessed can light is compressing duct work.

Ducts properly installed without compression and appropriately supported. Flex duct compressed by plumbing pipes. Duct to boot connection of jump duct is properly sealed with mastic. Right - The ducts are located in conditioned space in open-web joists between the floors and supported to prevent sagging. Right - Open-web floor and ceiling trusses provide space for ducts in conditioned space.

Existing Homes. SCOPE Additions If new flex duct is added to an existing home, either as part of an addition or an equipment upgrade, ensure that the flex duct is installed in runs that are as short, straight, and direct as possible and if any duct runs through building cavities verify that the cavities are large enough to have sufficient space to contain the duct without compressing it, as noted in the Description tab.

Existing Buildings In an existing building with flex ducts and an under-performing HVAC system, inspect for compression of the flex duct. Since it is often vital structure that causes the pinch-point, there are three alternatives: Re-route the duct.

Consider offsetting the added static friction that results from the longer run by increasing the duct diameter. At a minimum, ensure all curves are gradual, fully extend the flex, and provide ample supports to prevent sagging. Move the duct by finding a new location for the supply register sometimes possible or for the obstacle seldom possible. Below we have compartmentalized the ideas in a question and answer scheme.

We hope that this article answers you questions about flex duct sizing! Diameter is defined as the distance of a straight line passing from one end of a circle or sphere to the other end.

In other words, it goes straight across the circle. The diameter is a very important unit of measurement when it comes to flexible duct sizing because all duct sizes are measured according to their diameters.

Flexible ducting is normally sized according to the internal or inside diameter, often labeled as ID. It is quite easy to confuse circumference for diameter because they are both units of measurement relating to circles. It is very important to know the difference between the two, as they are completely different. Circumference is the distance around the circle. Circumference is not normally asked for in relation to flex duct sizing as diameter is more widely used for measuring flexible ducting.

OD stands for outside or outer diameter. It is the measurement of the diameter of the circle from one outside section to the other outside section of a circle. As a result, OD measurements tend to be slightly greater than the ID. They also easily conform to oval as well as round connectors. A good first step, or course, is to make sure there is effective communication among all the parties involved, including designers, framers, and HVAC, plumbing, and electrical tradespeople when installing flexible ducts.

The details presented here were captured from the U. Airflow is more complicated than it seems, and carelessness or disregard for these best practices can really come back to bite you. All ducts should be sealed using UL—rated duct mastic [1] , and flexible ducts should be held in place with tie wraps at all connectors. Ideally, all ducts should be located within the conditioned space. This is typically the case for ducts that run through a dropped ceiling or soffit, or between joists, so long as the floor system sits on top of a conditioned basement or crawlspace.

Attics can be problematic when insulation is located in the attic floor rather than in the rafter bays or, better yet, outside the roof sheathing. When flexible ducts are located outside the conditioned space, they should be sealed to prevent loss of conditioned air and also insulated to prevent thermal loss or gain from the ambient air.

All ducts, whether rigid or flexible, should be sealed with UL—rated duct mastic. Friction is the enemy of airflow. That creates slack in the duct, which reduces airflow for two reasons. To maintain strong airflow, plan for short, straight runs during the design phase. Pay particular attention to the framing plan, and route ducts through floor trusses where possible [2B]. Monitor the plan during framing and be prepared to create chases to carry ducts where necessary.

Also make sure that all ducts, regardless of length, are stretched tight between fittings. Avoid taking up slack with sharp bends [2A], which severely reduce airflow. Plan the framing package to include chases or trusses to accommodate ductwork [2B]. Ducts that are not stretched tight or that contain sharp bends can increase the equivalent length of the duct run by several multiples see illustration, above.

Airflow in a duct run of any length can be compromised by sharp turns or even kinks. And each turn, kink, or compression in a duct run reduces airflow, which results in more comfort-related complaints from your customers. Unfortunately, on many jobsites, poor planning of the framing and lack of coordination among subtrades result in all manner of bends and kinks, some of which all but stop airflow completely [3A].

Once the drywall is up, these problems are impossible to locate, so carefully inspect flexible ductwork before the drywall crew begins its work. Charts are useless without context. Not even getting into equivalent length and fittings, etc. Please add some context for the assumptions of these values.

Hello there, these are standard values HVAC technicians use.