There are many fundamentals to consider in estimating labor accurately and realistically for HVAC sheet metal and piping projects. The application of sound engineering principles, estimating experience and well documented labor studies assist in sound estimating. The following principles explore the calculation of man-hours rather than dollar costs. Labor hours are more accurately measured using man-hours as a constant factor rather than dollar costs. After total labor hours have been derived for an estimate they may be converted to dollar cost. In this manner man hour productivity rates can be developed and later converted directly to a dollar cost equivalent allowing for adjustments in wage rates for any area of the country, union and non-union wage rates, wage increases and adjustments for inflation. Tracking productivity rates for a project is likewise more accurate. The same fundamental may be applied to calculating man-hours in estimating ductwork by the per-piece or the pound. The author has undertaken countless hours compiling time studies, cost records and labor histories derived on the per piece labor costs for ductwork based on the size and types of ductwork fabricated. Conversion factors are used for calculating total pounds of ductwork which have been derived from a per-piece analysis.
There are many sources and techniques for deriving sound labor data for estimating that are available by analyzing job cost records, detailed time studies and previous estimates. A detailed analysis of this information can be compiled based on many factors that cause labor to vary. Some of the major factors that cause labor to vary for ductwork fabrication and installation are:
- The size of ductwork
- The type of ductwork
- The type of material used to fabricate ductwork
- The volume of the ductwork
- The number of duplications of ductwork
- The number of labor operations
- The number of component parts
- The productivity rate for manpower
- The building conditions
- Assembly required in the field
A careful analysis of cost records for previous similar projects, systems, and ductwork completed are some of the most valid sources of labor at an estimator's disposal. As an example if labor records for completed low rise office building indicate that low pressure galvanized ductwork was fabricated at 45 lbs/hr and installed at 24 lbs/hr under normal building conditions this labor data may be compiled for reference in future projects conducted under similar conditions. A detailed job history should accompany every project.
Time studies are a valuable source for collecting labor data. They may be conducted informally by observing and questioning personnel on the amount of labor required for fabrication and installation tasks. Asking a sheet metal mechanic the amount of time required to fabricate a 36"x 12" radius elbow as a spot check for your own labor estimates is good method for starting to develop labor records. Repeated time studies and spot checks are required over time to determine the true average and range of variation in establishing labor hours. Labor data when used in conjunction with previous estimates, which were prepared in detail and were found, to be accurate are valuable sources for labor data. Estimating experience is a vital factor in determining labor and man-hours as conditions such as understanding all of the operations for a project, tools required, and materials involved will also directly impact productivity rates and man-hours. Special conditions are included in the job history for future reference. Documenting a detailed breakdown and analysis of all conditions into its component parts and operations is an effective part of determining true labor cost. In calculating fabrication labor as an example you may have to consider indirect factors such as: shearing, set up, complexity of layout, material handling etc. in determining labor.
In calculating labor hours the data should be considered in relation to correlation curves and correction factors. Correlating these relationships will indicate that the unit of labor used is a true function of the factors to which it is being related. Making a quick calculation using curves comparing cost and labor with relation to the spectrum of sizes and type of ductwork being compared will verify labor accuracy. Cost and labor curves also provide a valuable graphic representation indicating how costs vary with size. Correction factors will adjust labor up or down based on variations in conditions, specifications and requirements. Start with common denominators for standard conditions and add or subtract percentages fro variations such as; floor, duct height, accessibility, local labor, special conditions, specifications etc. Ductwork over thirty feet requires a 1.3 correction factor over standard ten-foot elevation.
The final objective in estimating is to establish valid labor averages for each component included in the estimate. The labor averages should be corrected for variable conditions in the estimate based on labor studies and project specifications. The average labor applied should be based on a sufficient number of labor studies to meet a valid arithmetic average and range. The application of solid thoroughly documented engineering principles when applied in conjunction with judgment and experience will result in more accurate and realistic estimates and contribute to long-term success.