Just took a class.  Instructor gave her "opinion" - hot water heater, dishwasher, and refrigerator are 5 year property.  Most hot water heaters come with a 10-year warranty (irrelevant but helps to make a case for a shorter life than an HVAC).  Agree on the De Minimis. IRS capitalization rules went from $200 to $500 and are now $2,500 with the proper capitalization policy (I try to get signed copy) for my files.  Instructor disagreed with the "critical portion of the plumbing system" concept.  Then proceeded with 20 minutes of class disagreeing with each other.