Well, my house is somewhat older (built around 1900) and it's somewhat big so the upstairs doesn't keep cold air the same as the downstairs. With the central air on it's 74 downstairs and 78 or so upstairs. That's about as cold as I'll be able to handle it. The fish tanks are downstairs too, so it works out well to keep the tanks from getting too hot (though there isn't anything blowing on them so no fluctuations either).