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Ductwork Estimating 101

Ductwork estimating can be one of the most confusing processes in development and construction. There are a lot of formulas, sizes, materials, labor rates and factors to keep track of.

This is why many contractors choose to use specialized takeoff and estimating software. But what does this software do exactly?


The duct system, which transfers the conditioned air throughout your house, is one of the most crucial components in your HVAC system. A poorly designed duct system can lead to discomfort in rooms, expensive energy bills and premature wear of your equipment. Fortunately, there are a few factors that can help you determine the proper size of your ductwork.

First, you’ll need to know the square footage of your home and the size of each room. This information will help you calculate the total amount of ducting needed for your system. If you’re not comfortable doing this yourself, you can hire a professional to perform the measurements for you.

You’ll also need to consider the friction loss rate of your ducts, which affects airflow and is determined by the number of turns, filters, grills, coils and dampers in your HVAC system. You can find a duct loss calculator online to help you make this calculation, though it’s best to have an experienced technician do this part of the job.

Another important factor to consider is the size of your HVAC system, which is measured in tons of heating or cooling capacity. One ton equals 12,000 BTUs of heat or cool, and this will determine the total output that your ducts need to accommodate. The ducts must be sized to match the output of your system and provide adequate flow in each room to prevent hot or cold spots.

Finally, you’ll need to consider the cost of sizing your ductwork. There are several different ways to estimate the cost of your ductwork, including using the labor productivity of previous projects or looking at the number of square feet per man day it takes to install a specific type of duct.

The cost of sizing your ductwork will be affected by the size and shape of your house, the size of your HVAC system, the friction loss rate of your ducts and the labor productivity of your crew. Luckily, QuoteSoft ductwork estimation software can take all of these factors into account and create an accurate estimate for you in just a few clicks.

Friction Loss Rate

Ducts need to be able to move air without putting strain on the HVAC system or the ducts. This is possible if the ducts are sized properly, but there’s one thing that impacts how much pressure a duct can hold: friction loss rate.

You need to know the friction rate before you can decide what shape or size ducts to use. The friction rate involves your total effective length (TEL) and available static pressure (ASP).

TEL doesn’t just mean the length of the duct run, but it also includes the pressure drop and friction increase caused by things like coils, registers, grilles, dampers, and fittings such as T’s and Y’s used to connect duct runs. These accessories eat up a lot of the ASP that would otherwise be pushing air through the ducts.

Each type of fitting has a rating that tells you how much friction it causes in feet of ductwork equivalency. The rating takes into account factors such as how many pieces the fitting has, what kind of shape it is (square, 90-degree, 45-degree), and what type of material it’s made out of.

You want a high friction rate, because it allows you to use a smaller duct diameter and still get enough air flow. Conversely, a low friction rate requires you to use a larger duct diameter in order to maintain adequate airflow.

The reason for this is that friction reduces the velocity of air as it flows through the duct system, which in turn reduces how much energy it can take to move. This is why estimating professionals look at the TEL and ASP when determining duct sizes.

Duct estimating is a complicated task that involves a lot of math and specialized knowledge. Fortunately, programs such as QuoteSoft can help you prepare a complete marked-up duct, fitting, and equipment takeoff that automatically arranges items into groups, specifications, labor hours, item costs, materials, and job-related factors. Using a program like this lets you free up your senior estimators to work on the projects that will grow your business. To learn more about preparing a detailed ductwork estimate, contact us today.


Ductwork is the system that carries air from your central HVAC unit to the vents throughout your home. Its costs are determined by the size, type of ductwork, and installation method. These factors also affect the cost of repairing, replacing or adding vents to existing ductwork. Ducts can be made from many different materials. Each type has its own pros and cons. For example, flexible ducts can fit in tight spaces but may not be as durable as metal or steel ducts.

In new construction, the ductwork system is usually built into the house, which reduces installation costs. However, upgrading or replacing existing ducts in older homes can be more expensive. This is due to the fact that you must tear into finished walls and install a new system, which increases labor costs. In some cases, you must replace the ductwork insulation as well.

The price of ductwork depends on the materials used, the type and how much it is insulated. Uninsulated ducts can range from $10 to $18 per linear foot, while insulated ducts can cost up to $38 per linear foot. Exposed ductwork typically costs more than hidden systems, as the former requires more attention to detail.

Ducts can be made from a variety of materials, including fiberglass, steel, galvanized steel, aluminum and stainless steel. Stainless steel is the most durable, but it is more expensive than other types of ducts. Fiberglass is affordable but can break down quickly. Ducts that run through crawl space are generally cheaper than those in the attic or basement, but they can be difficult to work with due to limited accessibility.

Using an advanced mechanical estimating software program is the best way to calculate field labor. These programs provide accurate takeoffs and estimates for a wide variety of construction projects. They also have a library of standard material allowances, which can be modified for a specific project. The software can also calculate ductwork costs based on fabrication and installation labor productivity, which is measured in lb/man-day.

QuoteSoft Duct Estimating Software is easy to learn and includes a library of industry-standard specifications. Its estimating modules use SMACNA labor and bending allowances, which can be adjusted to your specific needs. The software supports a variety of file formats, including PDF, BMP, iSQFT and Dodge Plans. It also has an automatic measurement engine that converts CAD drawings into real-world estimates and quantities.


The estimating of labor to fabricate and install sheet metal ductwork is a key component to the estimation of a project. In calculating field labor time the estimator must take into account the number of pieces in a duct run, size of duct and fittings and any labor correction factors that may be applied to the estimating job. A good understanding of the process and a thorough knowledge of fabrication and installation methods are essential for accurate estimating.

Estimators must also establish a standard benchmark for the estimating job. This can be done based on labor studies or experience. This helps the estimator to compare cost and labor based on similar projects. It will also allow the estimator to determine a proper correction factor if needed. This correction factor could be based on size, location, local labor rates, specifications and other job specific factors.

Once the benchmark labor is established it can be used as a guide for estimating future jobs. The benchmarks can be based on labor per piece, pounds or square foot. Once the units are established they can be adjusted to a dollar cost allowing for changes in labor rates, union and non-union rates, wage increases and inflation.

The most common method is the Hours Per Piece estimating technique. This is a simple way to calculate a project’s labor. The total amount of hours to fabricate and install a piece of duct is estimated using the project’s takeoff numbers dividing by the fabricator’s historical labor productivity factor.

Using the Hours Per Piece labor productivity factor will help to keep the project estimates consistent and easy to read. Once the labor number is calculated for the entire job it can then be divided by the number of man days required to install all of the ductwork. For example 200 linear feet of main duct would be divided by 25 LF/MD (linear feet per man day) and the result is 8 man days or 64 hours to install the entire job.

This is a great advantage of the computer estimating software that QuoteSoft provides. Our estimating programs can perform the takeoffs directly from your CAD drawings, Dodge Plans or other file formats. We can then total the entire job with one click and automatically apply material costs, shop labor, field labor and any other adjustments. All of this information is displayed on a comprehensive report which can be broken down by sections, specs, areas, zones, item tags and more.