Somebody asked me this the other night at our club meeting and I didn't know the answer, here mid-winter. He has a single hive body that he believes is getting rather full. He wondered if it was okay on a warm day to add another hive body. My sense is that it would be okay with drawn comb but not if it was foundation only, based on heating the cluster only, not the hive. Would you advise adding or not? Obviously, he is concerned about swarming.