How big before humidty problems?

[FishyFishy!]

In my fish room, I'm lucky enough to have a window that I can keep open. But in this cold, I had to shut it. Even with my dehumidifier running all of the windows on the main floor have steamed up and I also have ice on the window in the fish room.

I think that an HRV is the best for sure. If you already have one I'd think you'll be just fine.