Is condensation bad for windows?

Bathroom windows will almost always "sweat" in the winter

When cold weather sets in, I invariably get a slew of questions from people worried about their windows “sweating.” There’s a perception, propagated by window salespeople, that condensation is a  sure sign that you need to buy new windows for your home. What’s the truth?

The photo above is of a north facing garden window in my master bathroom. In general, I keep the humidity quite moderate in my home but this window definitely shows more condensation than others. In this case, during a spell of temperatures in the low teens, a layer of ice even formed. Should I replace this window?

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