ACCA (the Air Conditioning Contractors of America) publish Manual J and Manual D worksheets and contractors used these forms to calculate residential heat loss and heat gain because they were the accepted method for calculating residential loads for decades.
Times have changed and Manual J and Manual D calculations are no longer performed on pencil and paper; contractors now use fancy software programs. Beware – the software programs have to be ACCA certified or your permit office will reject the results. The only ACCA certified Manual J programs are WrightSoft Right-J8, Elite RHVAC, EnergyGauge, Adtek and AccuLoads. All the developers claim to “save time and increase your accuracy with this easy to use load calculation tool”.
There are those who claim that the software takes the complexity away because the contractor never has to learn any math equations. Just take out of the box and use. We at Savoy Engineering Group have seen hundreds of inaccurate and flawed designs by people who do not understand Manual J, S & D theory. It is like the student who never learned simple math and now relies on a calculator – they do not recognize when the result doesn’t make logical sense.
The user of the software must understand how each parameter impacts the Manual J heat loss and heat gain results. What happens if I build the same house in different climates? What if the building
orientation changes? What about the insulation values of the wall and roof? And then there are windows – size, orientation, type, glazing, SHGC. And let us not forget about people and appliances. All of these factors and many more MUST be accurately entered into the ACCA certified Manual J software program. Otherwise, it’s garbage in, garbage out.
Most building codes and permit offices are now requiring Manual J load calculations, Manual S HVAC equipment sizing and Manual D duct designs. For example, the 2012 International Residential Code Section M1401.3 requires that “Heating and cooling equipment and appliances shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies.”
While, IRC section M1601.1 requires that “Duct systems serving heating, cooling and ventilation equipment shall be installed in accordance with the provisions of this section and ACCA Manual D or other approved methods.”
But then the government (US Department of Energy) puts on their website, “Homeowners should insist that contractors use a correct sizing calculation before signing a contract. This service is often offered at little or no cost to homeowners by … conscientious heating and air conditioning contractors.” What contractor has hours of free time to provide a Manual J load analysis to every person who is also getting 5 other quotes from contractors?
So it is clear the code is just going to get stricter. Make sure you select a Manual J & D provider who knows what they are doing, not just winging it. Also look for a provider that has easy to understand pricing, not “$149 + $0.14 per sq ft up to 3,000 sq foot, then an additional fee for….” – you need an accountant to figure out your price. We offer FAST, ACCURATE & AFFORDABLE engineering services for all your Manual J, S & D needs!