The HVAC Design and Specification Process

Building departments and green building programs recognize the need for proper HVAC Design, and are making it mandatory for building permits and certifications. All of them require a Manual J Load Calculation, Manual S Equipment Selection, Manual T Air Distribution, and Manual D Duct Design. These are the accepted protocol written by the Air Conditioning Contractors of America (ACCA).


  • Manual J Load Calculation: Finding the heating and cooling loads in the home based on the size and construction of the home. Without the information from this step, the results of the next steps will  impossible to achieve accurately.
  • Manual S Equipment Selection: Takes the calculation results from the first step and appropriately sizes and selects the equipment to be used for the heating and cooling. This can range from ductless or ducted mini-splits to gas furnaces to ground source heat pump (geothermal) systems.
  • Manual T Air Distribution: Correctly selecting, sizing and locating supply outlets and return inlets. This step looks at how to prevent drafts and stagnant air problems.
  • Manual D Duct Design: Includes Manual T Air Distribution protocol, and involves entering the selected equipment in to the software and connecting a duct system (or air delivery system) to it. This step not only involves the sizing of the ductwork to meet the performance and comfort requirements of the home, but we will ensure that the equipment and ductwork integrate in to the home’s architecture. This is one of the greatest advantages to having this done as early in the home’s design process as possible. It will avoid structural and aesthetic conflicts, and make sure it fits and delivers the right amount of air throughout the home, at the right temperature, and in the right spots.