I think of him as big in almost every way: he had a huge heart and helped so many people in so many ways, big and small, and he had a big brain, and boundless intellectual curiosity which led him to master a wide range of subjects and skills. This is not to say he was always open to every good new idea. He definitely followed Harry Truman's axiom, "Show me." But when presented with hard evidence, he would change his mind and his practice. He was a great teacher, always willing to share his phenomenal knowledge with others. I met Jeff as a colleague, working to improve the energy efficiency of affordable housing in Philly and across PA, and he became a very dear friend and neighbor. I have always been astounded by his energy, his courage, his ability to get big things done, and frankly by his humility. We miss him deeply.