Requiring every unique iteration of units to have a separate Manual J is burdensome, especially considering the small heating and cooling loads in many multifamily units, and large relative HVAC equipment size. Response: The HVAC designer can use their professional experience when performing load calculations on similar units. A unique Manual J (or equivalent calculation) must be performed on any unit that is expected to have a load difference of at least 25% from other units (based on different sizes or energy efficiency measures), or the next equipment size up, whichever is smaller. Separate calculations must be performed for each similarly sized group of units that have unique orientation and exposure.