There are a number of sources and methods for developing accurate man-hour labor figures for estimating and bidding hvac projects.

The sources for developing man-hour data are cost records, time studies, previous estimates, and trade experience. The skills and techniques involved in assuring accuracy in the development of the figures are understanding what causes labor to vary, correlation curves and formulas, labor correction factors, and the selection of suitable ranges of figures.

Using man-hours can be a more realistic measurement of labor, and can lead to more accuracy. Labor hours are a constant and they are easier to work with, as opposed to dollar costs, which can vary. Unit labor and productivity rates can be better developed with man-hours. Man-hours remain the same over time, given similar conditions, and they don't have to be reworked over and over again for variations in wage rates.

Labor hours don't change as wage rates do. They can apply to different areas of the country; they can be used for different union and non-union rates, for increases in wage rates, and for adjustments in inflation. Once the constant man-hours of labor have been estimated on a bidding project, the total hours are simply multiplied times whatever the correct wage rate is at that time for that location. For example, 300 man hours times $45 per hour results in $13,500 in labor costs. The same 300 man hours after a wage increase to $50 is $15,000

The approach of using man-hours for estimating ductwork labor is compatible for both estimating by the piece and by the pound. Understanding the principles and characteristics that cause labor to vary is vital to the accurate establishment of man-hours. Some of the major factors involved in fabrication and installation of sheet metal are:

  • The size of the ductwork or other sheet metal item is a major factor. A large 72"x30" duct may take 3 times as long to fabricate as small 12"x12" duct.

  • The type of the duct is a second important factor concerning labor such as rectangular or round, fitting or straight duct, and cleat connections or flanges.

  • The type of ductwork material, galvanized; black iron, stainless steel makes a difference.

  • The volume of ductwork effects labor, whether a small batch or large batch; the spread of setup and cleanup time varies.

  • The number of exact duplications in size and design of ductwork affects labor time.

  • The number of components involved making up a piece of ductwork; two "L" shaped pieces for a joint of pipe or 10 pieces for a radius elbow with multiple gores.

  • The productivity rate of the manpower being used - seasoned mechanics or apprentices.

  • The effect of building installation conditions effect labor: 10 ft high ductwork or 20 ft. high; first floor or the 15th floor.

Assembly required in field where items are sent disassembled. Cost records. Actual labor on previous projects already completed, with similar systems, equipment and ductwork, is one of the most valid sources of labor available. For example, the labor records on the previous low rise office building show the low pressure galvanized ductwork fabricated at a rate of 45 lbs per hour and installed at 24 lbs. per hour under normal conditions. This labor may be documented for reference when estimating similar projects in the future.

Times studies are a valuable source for compiling labor data. Formalized time studies may be conducted along with more informal means, such as observing and questioning personnel regarding the amount of labor required for fabrication and installation tasks. Repeated time studies and spot checks are required over time to determine the true average and range of variation in labor hours.

Previous estimates that have been prepared in detail and found to be accurate are valuable sources for labor data. They may be measured against data compiled in time studies as a method cross checking the accuracy of the information. Special conditions and other extraneous factors should be taken into consideration also.

Trade experience can be an important factor in determining labor and man-hours. Experience in the shop or field can provide a detailed understanding of possible hidden costs for some items. Set up times, the detailed operations, and the tools and material required, all impact productivity rates and man-hours, and the actual knowledge of these factors enhances accuracy.

Detailed breakdown and analysis of special complicated items, where labor data is not available, into their component parts and individual operations, is an effective way to estimate the labor for these items. For example, break down a large kitchen hood into its individual parts: top, sides, ends, gutters, etc. Then calculate the labor for each part separately based on each operation such as layout, shearing, forming, etc.

Correlation formulas and curves are valuable tools in analyzing and establishing labor hours. Correlating the labor of items to the units of measurement, sizes, types, features, etc. is vital, in validating that the unit of labor is a true function of the factors it is being related to. For example the installation labor to install air handling equipment such rectangular grilles and diffusers, fire dampers, motorized control dampers, and so on, relate more accurately to the perimeter of the item, rather than the face area.

Labor correction factors are used to adjust basic labor units up or down based on variations in conditions and specifications. Start with common denominators for standard conditions and add or subtract percentages for variations such for duct heights above the floor, higher floors, accessibility, local labor productivity, and so on. For example, ductwork 30 ft. above the floor needs a 1.3 correction factor over the standard 10-foot height duct run.

Labor averages. The final objective in estimating labor accurately is to establish valid labor averages for each component for a specific size or size range. The average labor applied should be based on sufficient number of labor studies to meet a valid arithmetic average for the range it is applied to. For example the average labor may apply to galvanized radius elbows which range in size from 18"x12" to 24"x12". Thus, when estimated in a typical system and size batch, the labor will balance out closely to the established average figure for the actual mix of sizes in the specified range.

Please note that there are various sources of labor man-hours, and established sound procedures for estimating hvac projects.

(Wendes Systems offers several such manuals including the recently published second edition of the "Wendes Mechanical Estimating Manual," which covers detailed labor data, charts, procedures, sample estimates and forms. Contact Wendes Systems, Inc. at 3105 North Wilke Road, Suite W, Arlington Heights, IL 60004; 847-818-8371; www.