In the US, people spend the overwhelming majority of their time inside buildings that burn fossil fuels, which are bad for both the environment and human health. (Think: breathing in air pollution from gas stoves, furnaces and water heaters.) If we're going to fix this problem, we need to retrofit millions of buildings with all-electric equipment, says energy upgrader Donnel Baird. Hear about his ambitious plan to rip the fossil fuel infrastructure out of aging buildings and upgrade it with smarter, cleaner, healthier technology.