There’s many local codes now requiring Manual J and Manual S calculations for every new home and remodel that changes the load of the house. The fact is, very few HVAC contractors know how to properly execute either calculation.
Although advances in building insulation are rapidly changing the profile of the average American home, the typical HVAC contractor still selects an air conditioning system for a home based on the old rule of thumb of 500 sq. ft. per ton. Unfortunately, most contractors are afraid to change this long habit of ‘guesstimating’. This ‘fear factor’ holds many contractors in design paralysis. In a new home, this practice can have disastrous consequences. As the building envelope is made more efficient and the effective R-value is dramatically increased by the use of spray foam and other high efficiency insulation measures such as SIPs, ICF and dense pack cellulose, the size of the air conditioning equipment should logically decrease.
A well-constructed high-efficiency building envelope can and does change the rules.
ProCalcs years of experience indicate that when properly assembled, a super efficient home can be cooled with an A/C unit as little as half the size of one used to cool a conventional home.
Consequently, this helps HVAC contractors avoid the common install issues related to oversized equipment in high efficiency homes.