I never heated DS bottles, we travel a lot and didn't want to get 'caught out' with nowhere to heat it and have him screaming because it wasn't what he was used to!
He had it straight out of the fridge a couple of times, granted, like you mentioned, it was summer and HOT!!! but he didn't seem to mind at all! He is a greedy little munchkin though

I never expressed for night feeds, I wonder if serving it cold would wake them up instead of get them sleeeeeepy x