So when I hear 1820s i think about the air leak issue. Sometimes you save more sealing everything up and keeping your old window units. U may even notice you're taking one out once it's all sealed.We were really looking to put in AC since the house is 1820s and we're still on window ACs. These guys want to all basically put a heat pump in with a handler in the attic and in the basement. The main selling point is basically the heat functionality since we have an old combi boiler and radiators that's oil which is crazy expensive to run. They say we can run cool and hot with this system and it's 100% efficient at 5 degrees outside and will run until -25. That would allow us to basically just run the oil for hot water and the couple nights a year we get below 0. Heat pump system is basically about $15k cheaper then separate central air and new furnace install