Set your thermostat as low as is comfortable in the winter and as high as is comfortable in the summer.
Clean or replace filters on furnaces once a month or as needed.
Clean warm-air registers, baseboard heaters, and radiators as needed; make sure they’re not blocked by furniture, carpeting, or drapes.
Bleed trapped air from hot-water radiators once or twice a season; if in doubt about how to perform this task, call a professional.
Place heat-resistant radiator reflectors between exterior walls and the radiators.