Equipment. Most sources repeat the same advice: oversized furnaces and air conditioners cost too much, waste energy, and sometimes provide lower levels of comfort. To avoid these problems, the first step is to insist that your HVAC contractor perform a Manual J calculation to determine. Several energy experts have commented on the GIGO problem, including John Proctor, Hank Rutkowski, and Allison Bailes. Hank Rutkowski, the mechanical engineer who wrote the original Manual J document, was recently interviewed for a profile posted on the Green Building Talk Web site. The program will then automatically assign the CFM values to each duct based on the load calculation results, calculate all the sizes, redraw all the ducts at their proper width or diameter, and calculate all the pressure losses. Most residential furnaces, boilers, and air conditioners are still sized by rules of thumb instead of careful calculations. As a result, almost all of the HVAC equipment installed in U.S. homes is oversized. Elsewhere, Michael Chandler wrote that his local planning board was still not even enforcing the Manual J requirement which results in inefficient, oversized air conditioners and attendant humidity and mold problems. Even though reps of the local HBA pointed out the benefit of requiring Manual. Dozens of studies have confirmed that the degree of oversizing typically ranges from 30 to 200. Builders and homeowners who ask HVAC contractors about Manual J and Manual D calculations are usually met by a blank stare. For the calculations to be meaningful, information on all of these factors must be correctly entered into the software program. Manual J and Manual D calculations are required by most building codes. The 2006 International Residential Code requires (in section M1401.2) that Heating and cooling. He adds 5 to 10 degrees to the summer and winter design temperatures, calls the building average instead of tight and doesn't take credit for shading by interior blinds and drapes. Then when he finally comes up with a load number for sizing, he throws. Powered by ACCA Manual D - Residential Duct Design. Wrightsoft Right-D Windows Elite Ductsize Windows Adtek Accuduct. Windows Standards Codes Corporate Partners. The piece notes, Rutkowski estimates that only 10 of heating and cooling equipment sizing decisions are based on some type of Manual J calculation and that less than 1 of the jobs are based on an aggressive implementation of the recommended design procedures. The Pressure Changes Graph report will show you the static and total pressure available at each point along the route with the highest static pressure loss. Manual J and Manual D are calculation worksheets published by the Air Conditioning Contractors of America (ACCA ). For many years, these worksheets have been the standard methods for calculating residential heat loss, heat gain, and duct sizes. That may be his way of saying that he doesnt know how to do it, but the fact remains that this is a very common situation with residential HVAC contractors who can barely implement Manual J.