Perfect sleep today at 16°C/61°F I might start the AC to precool the bedroom a bit earlier cause it takes awhile to get there Even though it's 19°C/66°F outside at night in Portugal, without AC our bedroom would be 30°C/86°F with 2 people in it Why? Well when we travel and we don't cool it, our bedroom at night is about 24°C/75°F, so that's the base temp And that's because it's a well insulated modern house (aka the blessing and curse of modern houses), modern walls delay the heat from the sun in the day so it heats up your house at night, essentially to save energy but it results in extremely hot bedrooms that are terrible for your sleep On top of that two people sleeping increases a bedroom temperature by another 3°C!/5°F. Especially if you work out and have some muscle mass which radiates even more heat! So without AC running we'd end up in a 27°C/81°F bedroom! Add a blanket to that and you add another 3°C, so you're sleeping at 30°C/86°F. Terrible sleep! If you ever slept in an old house you know how nice it is, it's barely insulated and feels breezy and cold at night, how it should be Overheating at night due to modern insulated homes is a well documented problem in energy efficient housing research So yes most of us need AC at night!