Ductwork takeoff is an essential part of the sheet metal estimating process. Getting this right is critical to an accurate bid.
Round duct branch takeoffs are the most common type of takeoff. However, these fittings can have an airflow penalty due to the 90-degree turn. Fortunately, there are other types of takeoffs available that can reduce this issue.
Types of Takeoffs
Duct takeoff services are an essential part of any construction estimating process. These estimates help contractors determine what materials are required to complete a project. The cost estimator will use information provided on the blueprints or architectural plans to compile a list of materials and their prices.
These estimates are important because they provide a detailed, accurate, and up-to-date list of all the necessary components that will go into making up a ductwork system. The resulting report will allow the contractor to plan how much material is needed and how long it will take to complete the project on time. It will also allow the contractor to know the exact cost of the materials required.
A poor quality ductwork design can have major consequences that impact building occupants. This includes problems like stuffy air, drafts that don’t move properly, hot and cold spots in the space, and unbalanced air pressures that expose occupants to high levels of dust, pollutants, and odors. Many of these issues can be traced back to bad ductwork designs.
While preparing a ductwork takeoff, it’s important to keep in mind the physics of air flow and the specifications of the heating and cooling equipment used for installation. Using the proper fittings can help to ensure that the ductwork is sized correctly for optimum performance. The right fittings can also help to reduce the amount of energy a ductwork system uses to operate, which can have positive impacts on an entire building’s energy costs.
There are two different types of ductwork takeoffs that can be prepared: manual and digital. Both serve the same function and offer the same information, but they differ in how they’re produced and the time it takes to create them.
Digital ductwork takeoffs can be produced using software solutions that work with various CAD drawings. These programs will let the user select which layers to view and can highlight specific areas of the drawing in a variety of colors. Some programs will even let users pause the takeoff to get a closer look at a certain area.
Round Takeoffs
Unlike rectangular duct, round duct is shipped to the job site in longer lengths and snapped/secured together on-site by the contractor. This can result in a lower upfront cost for the contractor and less material waste. Round ductwork also tends to have more airflow efficiency than other shapes.
Nevertheless, round ductwork has its limitations. When the main trunk line meets a branch duct the opening to this fitting must be at least 25-30% larger than the corresponding branch duct side to avoid an airflow penalty (see Figure below).
This size restriction, plus the fact that round ducts are not as rigid as rectangular, can create a serious problem with airflow when it comes time for the contractor to add a takeoff at these points in the piping system. Typically, the contractor must use some form of a “scoop” takeoff to allow air to flow into the branch duct.
Directional takeoffs, which look like metal scoops or extractor fittings with turning vanes that protrude into the airstream, are often used to solve this problem. These takeoffs allow for more airflow to enter the branch duct by creating a funnel effect that directs the stream into the fitting. However, they can create problems if they are not properly spaced.
When you place directional takeoffs too close together in a row they will create an area of high pressure that can cause air to clog the duct and reduce system performance. The ideal spacing is to stagger these type of takeoffs 18 to 24″ on center from each other. This will allow each takeoff to relieve the pressure from the previous ones and regain its turbulent flow.
Getting takeoffs right requires a great deal of knowledge about the equipment being installed, physics of airflow and estimating formulas, materials, specifications, labor rates and factors. It’s not an easy task for part-time or entry-level estimators to master. That’s why it is important for contractors to find a takeoff tool that can simplify the process and enable junior estimators to work on critical projects with more confidence. Fortunately, takeoff software such as QuoteSoft Duct can help.
Directional Takeoffs
Using directional takeoffs is one of the best ways to get airflow from a main trunk line to new branch ducts. These fittings have some form of a metal scoop or extractor (turning vanes that protrude into the airstream) to grab and direct air into the branch duct they connect to. Directional takeoffs may be more expensive than other types of ductwork takeoffs but they are worth the extra cost for increased airflow performance.
A typical commercial job has a large rectangular trunk duct line that disperses the cooled or heated air into the branch ducts to service each room in the building. In order to have the proper airflow distribution, the top of each duct must be high enough and the bottom of the duct must be low enough.
This is why many engineers draw the main trunk duct lines in a “rectangular” shape rather than round and often have directional takeoffs shown in plan view on the right-hand side of the drawing. These directional takeoffs are shown with an arrow that indicates whether the duct is going up or down. The arrows indicate that the directional takeoff is UP and will increase the bottom of the duct, or DN and decrease the bottom of the duct.
These directional takeoffs are a common solution for directing air into the bottom of the ducts when a main trunk line ends up being too high. However, the directional takeoff can also cause problems when used on the side of the duct where there is an air change (elbow or transition). In these situations, the directional takeoff can prevent the necessary turbulent flow to enter the next duct downstream and the airflow will be significantly reduced.
Ductwork estimators are faced with a lot of formulas, complexities, materials, specifications, labor rates and factors when performing their takeoffs. Getting accurate estimating results takes a lot of time and experience. A reliable duct estimation software program can take care of the calculating for you, allowing senior staff to work on the important jobs that will drive your company’s profits. QuoteSoft Duct Estimating Software is a fully-featured takeoff application that performs takeoffs directly from plans on your computer screen. Custom specifications and standard labor times can be programmed into the software so that you can use them for any type of duct system.
Top Takeoffs
The top takeoff is the avenue by which air moves from a main trunk line to an individual branch run of duct. It’s important that this duct takeoff is designed well so that it transfers the maximum amount of air possible into the new duct run. A poorly conceived and installed top takeoff can cause air flow issues in the rest of the system. Those include stuffy or drafty buildings and uneven air pressure that can lead to odors, allergies and other health problems.
These problems are often the result of poor estimating and design work. This is especially true for ductwork systems where the HVAC equipment can be positioned in different areas that impact the way the ducting is constructed.
Duct takeoffs that don’t account for the physics of airflow can result in an imbalanced and inefficient system that costs the owner more than it should to operate and maintain. In addition, a lack of attention to the duct takeoff process can also result in excessive air loss and wasted energy.
A good estimating program should help contractors with the takeoff process by organizing items into groups and specifying a standard labor time for each item of ductwork or fittings. QuoteSoft’s ductwork estimation software is programmed with SMACNA specifications that are easily modified to match your company’s standards. The software also allows you to highlight individual items in a variety of colors and to zoom in and out on the drawings for more detailed views.
Having a clear view of the plans is essential to making an accurate takeoff. It’s important to be able to see the scale of the drawings, how the different parts and components are labeled and to be able to easily select and deselect each part as you perform the takeoff. In some cases, a building drawing may be layered with different layers that make it difficult to find the layer with the ductwork. This can be overcome by using a takeoff tool that offers the ability to deselect each layer for a clearer view.
Another tool that will help with the takeoff is a CAD drawing add-in like QuoteSoft’s Duct Estimating Software. This tool makes it easy to mark up the ductwork and then export the quantity into Excel or any other spreadsheet app for instant material and labor costing. It’s fast, intuitive and customisable for your own unique requirements.