Spring: Never, my partner is allergic to tree pollen released during the spring, nor does the indoor temperature warrant opening the windows Summer: Sometimes in late summer - I am allergic to grass pollen highly prevalent in early summer. Once they clear, I open the windows when it’s warmer inside than outside, to cool down my apartment slightly Autumn: Rarely. The temperature usually does not warrant opening the windows Winter: Never. It’s far too cold to let heat intentionally escape