The first way you can watch Flames Games online reliably is through NHL Gamecenter. Although that option isn’t free you are assured you won’t miss a game. Albeit, there are still weird blackouts if you’re an avid fan in Calgary. Calgarians who have cable get every single game with Sportsnet. The odd game will be on nationwide on CBC.
And another option for those who can’t get a handle on the subscriptions: REddit NHL Stream. Look each game for the unique streams posted online.