They gathered together on a sunny July evening, between the churchyard’s trees and leaning tombstones, to give thanks for the heat pump. The previous month, a flatbed truck carrying a hefty new heat pump system had eased itself onto the church grounds. So now, after more than 800 years, St. Mary’s has gone electric. “We want to get through winter knowing that we’re going to have a nice warm church.”Dozens of churches in Britain—commonly heated by oil or gas boilers—are currently in the process of installing electric-powered heat pumps as part of eco-minded retrofit projects. And yet, it can be difficult to install heat pumps in older places of worship, which tend to be large, uninsulated buildings.