The Must-Knows of Premium 20x20x2 Furnace Filters in Canada: How Often are Replacements Necessary? Interested in quality 20x20x2 furnace filters in Canada but aren't sure how often they need to be replaced? Don't worry, this in-depth guide to everything furnace filters has all the answers you need. You'll learn what... The Must-Knows of Premium 20x20x2 Furnace Filters in Canada: How Often are Replacements Necessary? Interested in quality 20x20x2 furnace filters in Canada but aren't sure how often they need to be replaced? Don't worry, this in-depth guide to everything furnace filters has all the answers you need. You'll learn what...