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Typically this is about 18 minutes per pound but Iâll sometimes pull mine out about 20 minutes before that since it will stay warm in the tinfoil (and even room temperature ham is MUCH better than dry)! Most directions for cooking a spiral sliced ham tell you to reheat your ham at 275F and I agree with this method.
1 Ham labeled Fully Cooked or Ready to Eat.  Preheat the oven to 325Â°F. To heat the ham, place it on a rack in a shallow roasting pan, and bake uncovered. For a whole ham, allow 15 to 18 minutes to the pound; for a half, 18 to 24 minutes per pound. The ham will be ready when the internal temperature reaches 140Â°F.