Whether you need a blow off tube depends on what type of yeast you are doing and at what temp you are fermenting at. Being in Nova Scotia I don't believe you'll have too much of a heat problem (especially at this time of year). I make it a point to ask my LHBS how much activity to expect out of the yeast I am buying from them. I.e., Does the yeast ferment aggressively, or does it have a tendency to to be a little slower?
Writing down everything that happens to your beer in a log/journal will help you keep track of what beers/yeasts require blow off tubes.