Really, David you should aerate the old compost maybe once a week with a little stir, using maybe a digging fork to turn the outside stuff in to the middle. You do want to make sure you don't go back to an anaerobic state in the old pile. Too much aeration is better than not enough. If it's 'working' well, the turning process won't hardly slow it down.
When you turn it, you should encounter a hot area in the midst of the pile. If it's cooled off, that's an indication it's used up most of its air and fuel in the middle and it needed turning.
