I moved to my apartment in June. Right now in the living room and master bedroom, there are holes in walls for aircontitioners. These are large, sized for wall a/c units. My standard size window a/c unit is sitting in in that space in my bedroom and it is way too small for it. I put a bunch of foam strips around it to cover the space and to not let extra heat in. For the purpose I need it right now, this set up is working and I can run my bedroom a/c when I need it.
In my living room, the hole is just open. There is a metal cover that would go over the hole, but it doesn't provide any insulation whatsoever. Basically, these look like large holes in the wall, with metal box attached on the outside of the building creating a niche on the inside where a/c unit sits. The metal box outside is perforated, so that there is a free air flow.
It's fine now, that is summer, but in the winder this will basically be two large open holes in my walls. There is no way I would be able to keep apartment warm regardless of the heat setting I use. The wall unit a/c are designed to just sit in these openings year round and they themselves provide insulation to the inside space. But I am not going to buy those. I'll keep my current window unit in the bedroom, and I should be ok without a/c in the living room next summer. I made it through most of this summer without it, so it's going to be fine.
How can I insulate these for the winter? These would have to be non-permanent solutions as I can't alter apartment and cover these up permanently. For the same reason, I don't want to use spray insulation.
Does it make sense to buy a roll of fiberglass insulation and stuff in these two holes? I'm would be concerned with having fiberglass open to the apartment for safely and cleaning reasons.
Any suggestions would be appreciated.