Of course it's not actually infinite. but I dont use heating except maybe one or two days a year at those super peak lows (-35°c let's say). I wish it was separate on the bill so I could give you a number but it isn't.
In Québec most building even with water heating use electricity, older houses might be different as for my apartment, it's in a house basement but it's definitely on electricity as well.
As for summer, I dont mine in heatwaves and yes I crack a window open. Being in a basement keeps it relatively cool.