Many ham preparation guides will tell you to heat your ham for X minutes per pound at Y temperature. As long as you use a thermometer and don't set your oven too high, your ham will reach serving temperature without drying out. Some folks like to add liquid or lemon slices to the bottom of the pan, but this isn't necessary. If you don't have foil, you can use a cooking bag, or even a large oven-safe pot with a lid set ajar. Loosely wrap the ham with foil, set it in a roasting pan, and you'll have everything you need to keep your ham nice and moist. Foil is the easiest vapor barrier to apply, and it's foolproof. You don't want to miss Juicytown and end up in Jerkyville. But being able to measure your target is the best way to avoid overshooting it.

The most important tool to help you properly heat a spiral ham isn't an oven-it's a thermometer. You don't want to dry out the surface in the process however, and heating too aggressively will rob the ham of its succulence (to the point where neither a maple syrup glaze nor mustard could improve the situation). Since it's a large piece of meat, warming should go low and slow because it takes time for heat to penetrate all the way to the bone. Your ham is already cooked, so it only needs to be brought to a suitable serving temperature, which is about 140☏.

Heating up a spiral sliced ham