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Ductwork Estimating 101

Ductwork is one of the most difficult construction elements to estimate accurately. However, it’s also one of the most crucial for boosting energy efficiency and improving home comfort.

Unlike other construction elements that can be estimated using standard takeoff formulas, ductwork requires a unique set of skills. Luckily, there are ways to streamline the process and save time.

Estimating a Duct System

Ductwork estimating requires a good understanding of how to calculate air flow and how duct sizes influence each other. A general contractor may use a sizing chart, software or other calculation methods to help them arrive at an accurate duct size estimate.

The first step in calculating the duct size is to determine how much CFM (cubic feet per minute) the HVAC unit can output. This is accomplished by multiplying the unit’s tonnage by 400 and then dividing it by the square footage of the home. This gives you the total output in CFM the house needs to be properly conditioned.

Once you have this number, you can begin to determine the duct size needed for each room. This is done by running a tape measure around the walls of each room, and dividing odd-shaped rooms into rectangular areas, if necessary. The measurement is taken in feet and inches, and the duct dimensions are then entered into a duct sizing chart or software program.

A good duct sizing chart or software will also show the maximum friction rate of the system. This is the amount of pressure loss or “static” that can be tolerated without causing too much noise, air loss and/or waste. The maximum friction rate is determined by a formula that takes into consideration the type of duct material, its length of run and how many duct fittings are used (each has a different friction rating). A standard value for most technicians is 0.1 wg.

Getting Started

Ductwork is an essential part of any home’s ventilation system and air-conditioning equipment. Without properly installed ducts, your HVAC systems could produce dangerous carbon monoxide or otherwise not distribute heated and cooled air throughout the entire house. This can be a big problem and make your house uncomfortable. A well-designed ductwork system will be worth the cost in the long run.

Ductwork estimating requires a lot of calculations that are different from other construction elements. Unlike lighting, doors and frames, glass panels, concrete or steel, which are easily evaluated by standard spreadsheet programs like Excel, estimating ductwork is complex and time consuming.

It is helpful to work with a software program that can streamline your mechanical estimating process. This can help you win more jobs, reduce project timelines and increase your profits. A system that provides a large library of mechanical assemblies is particularly helpful. This helps you more quickly build your estimates and eliminates the need to create a database of items on your own.

A comprehensive estimating tool for sheet metal contractors will provide the calculations you need in one easy to use package. FastDUCT is a comprehensive HVAC estimating software that includes a built-in catalog of over 250,000 items for a complete takeoff and a wide variety of calculations in square feet, pounds, materials and shop labor hours. It can also generate an Excel bid summary and report based on the data you specify. It also allows you to create your own custom spec files, and is pre-loaded with a ductwork spec file that includes spec sheets for sheet metal raw materials, duct liner, tees, joints, stiffeners, tie rods and duct accessories.

Per-Piece Method

When estimating sheet metal work, it’s necessary to know how many hours of labor it takes to install a specific section of duct. This will help in determining the pricing for the project. The per-piece method allows for a direct correlation between unit measurement and labor expended as it looks at individual component costs. It also compensates for a mixture of straight duct, duct gauge sizes and fitting types as it uses a standard ratio for each type of system.

When you’re sizing air ducts it’s important to consider the square footage of the home as well as each room. Sizing for a rectangular house will require more duct than a two story house of the same size. The layout of the rooms is also important as sizing for multiple vents in different locations will increase cost.

When estimating the cost for a duct system, you must take into account the number of vents required as this will increase the cost of the main trunk line. The number of vents will also determine how long the duct run must be. The cost of the vents varies depending on their style and size but you can expect to pay about $200-$250 for each vent plus a small amount for the insulation that will keep the air at the proper temperature and prevent heat loss.

Average Method

Unlike construction elements like glass panels and doors, ductwork is not easily evaluated using standard unit pricing. Instead, a contractor must evaluate their labor inputs based on a combination of factors including square footage, duct size and shape, round vs. rectangular duct diameter, and labor productivity units.

These factors impact the total price of your duct replacement project. Ducts can be made of a variety of materials, with aluminum and galvanized steel being the most common. The location of the ductwork also plays a role in overall price. Hard-to-access locations in the attic, crawl space or basement may increase duct replacement cost.

Lastly, the duct system size and the type of fittings are important. The larger the duct system, the more costly it will be. For example, a rectangular duct system requires more material than a circular duct system. The same is true for the amount of duct insulation required.

The PriceDuct estimating software has been built to provide an accurate estimate for the installation of new ductwork in a home or business. It’s easy to use and is based on the latest SMACNA construction standards. Whether you are working with old and worn ductwork, replacing air filters or just looking to upgrade your existing ac system PriceDuct makes it simple. Sign up for a free trial today!