Mr. Pealer suggested we start by studying our homes. A high-efficiency HVAC system may eventually be a great investment, but it shouldn’t be your first. Your first step should be to figure out where your heated or cooled air is escaping from your house and then take steps to stop it from escaping. “Limit the waste and then figure out efficient ways to produce what you do need,” he said.

Start by actually reading your utility bill, and not just the total at the bottom. Pull up the last 12 months to get a better sense of how and when you use energy. Next, get an energy audit of your home, a process in which a technician pinpoints where a home is wasting energy and then suggests ways to reduce the waste.

Bringing water to and from your house uses energy too, so reduce water waste. You could, for example, install a smart monitor like Flo by Moen, which detects leaks and allows you to remotely shut off the water to your house from your smartphone.

Small changes can have a substantial impact.

Consider Ann Jacobs and Brad Brunson. The couple was living in an 1897 Victorian house in Milwaukee that was so drafty in the winter they had to use space heaters in the living room to stay warm. “It was horribly cold,” Ms. Jacobs, a lawyer, said of the time in the early 2000s. And the heating bills were out of control. “They were just hundreds upon hundreds of dollars,” she said. “It was just beyond belief.”

Friends suggested they replace all their windows, an expensive project for a house with 16 windows on the front alone, many of them made with leaded glass, which provided character and matched the architectural style of the home. First they got an energy audit, with the auditor testing how air moved through the house and where it escaped.

They learned that the walls had no insulation and heat was escaping through the attic and basement. So they insulated the walls and attic, and replaced only the basement windows, a project that cost substantially less than what it would have cost to replace all the windows in the house. “All of a sudden we had a house we could live in,” Ms. Jacobs said. “People underestimate that little changes make a huge difference.”

The easiest time to go green is when you’re renovating, like when Ms. Karn renovated her Margaretville home. In a project that took 10 months and cost around $130,000, she took the house down to the studs.