Because these rules of thumb almost always result in gross oversizing of cooling equipment, most energy experts have been battling rule-of-thumb sizing for years. However, rules of thumb have their place. Using a rule of thumb is not really the problem; the problem is that HVAC contractors are using a bad rule of thumb.

Whenever you have the ability to precisely calculate the cooling loads. Then do it instead of using the rules of thumb


References for presentation:


1. HVAC equations, data, and rules of thumb.

2. Mechanical engineers hand books