A look at the difficulties of getting good HVAC design in high performance homes. Most HVAC professionals are not familiar with the design requirements of very energy efficient homes with tight envelopes. Most rules of thumb and the very basic modeling that is done in support of sizing the systems implicitly assume a “code” home… which is the least efficient house you can build without getting sued. Oversized systems cause different problems than undersized ones, but they’re still significant problems. As high performance homes become more common, more people are running into these issues. Better contractor, builder, and homeowner education is needed.