Matt Risinger speaks with John Semmelhack from Think Little at the 20th Annual Westford Symposium on Building Science Nerd Camp about what's on him mind in building science. In high performance homes, Semmelhack is really focusing on indoor air quality, improving comfort and durability, plus saving energy. Mold is, of course, a major issue in the minds of many now and he notes that about 99% of moisture issues in buildings comes from bulk water, whether that be rainwater or ground water. Dealing with that solves most moisture issues, and therefore mold issues.In the HVAC design world, Semmelhack's bread and butter is ducted mini-split heat pumps, where you can enjoy the benefits of variable speed compressors, small units that are appropriately sized, and efficiency for a relatively low expense. Ductless units, on the other hand, may not be as efficient as the ratings have shown them to be. In a dream setup for a 3,000 square-foot home, he'd include a pair of ducted heat pumps, with an independently ducted ERV. If the house were two stories, there would be one setup on the first floor and another on the second.These days, Semmelhack's brand of choice is almost primarily Fujitsu for heat pumps and RenewAire for ERVs, especially the EV90 and EV90P. In terms of filtration, he often uses MERV-13 filters for heat. Watch the video for some more of John's expert advice.