I live in a pretty old house in the midwest, built 1929, bought in '21, single-story, ~1300ish sqft, and with a large, spacious basement. Every time summer comes around I've had issues with the basement getting MUCH colder than the rest of the house (like >10 degrees F difference), presumably due to poorly-insulated floors and cold air sinking. The HVAC is still capable of keeping the main floor at the temp set on the thermostat, but the temperature differential indicates it's working quite a bit harder than it really needs to be, and is probably wasting quite a bit of money.