When I lived with my DD we figured out that the space heaters (oil filled ones) were way cheaper than running heat and window units cheaper than central air. The one year she ran her central heat . Electric was over 400 and gas over 300 that was nuts. We cut that by more than half . She had a older 1950's home so not a lot of insulation . We did manage to get a little put in before she lost her job then the house.