QA: Extra combs from OA treated hives, hive ventilation

I will try to collect some question and post some answers that I would fill they might be of the wider interest. This two I've got in this spring.

Q1: If you use oxalic acid fumigation in the fall, does it affect the honey left over from winter?  Can you extract that honey or is it best to just feed it back to the girls?
A1: Oxalic acid as it is used in the hives leaves some residues in the honey, but levels are far bellow of the limits for the food consumption. From that point of few “honey” as you mentioned can be consumed. But regardless of that, winter stores are not real honey, because in most cases it is based on sugar feeding. At list never sell such extracted “honey” to the consumers. There are several possibilities. Full combs if they are not dirty (potential Nosema infestation) can be used for making splits. Nice partially field can be used back in colonies, but better in the brood chamber. Scrap the wax covers of the honey and bees will empty the cells and use for the brood. The safest way of use is to extract and use for fermentation for med or if not perfect taste, distill for brandy (be aware of legitimacy for doing that!).

Q2: Under what conditions would the rear door flap(s) be opened? One or both upper and lower? My recollection is that you said in very hot weather or in winter if you have foam in the back and wish to let condensation escape. Does it help with air flow when they are drying honey for example.

A2: It is true that flaps were constructed mainly to insure ventilation during transportation. Later have been recognized that at list upper one can be opened also during the winter when you have installed foam inside. I open them also during high nectar intake to make them easier with ventilation of the hive. If the bee house is not to bright, too much daily light than this will not disturb them. In such case is good to shade the windows as well. In hot regions it is also good that bee house has at list good passive ventilation, taking colder air from the back or side and release it at the top.
It is good to mention her that some professional beekeepers are using only foam through out the whole year, no extra doors at the back. Especially when they build several hives together as a chest.

Upper flap opened in this new hive (upper door opening in the book)