My apartment is the upper level of a house. I have my own front door that leads to an indoor staircase that goes up to the entrance of the apartment. However, this staircase area is not separated from my actual apartment by a door. My question is, in the winter, would it be better to block that off somehow (like with vinyl strips) so I can keep the warm air in my apartment, or would it be better to leave it so any cold air will sink down?
yes a floor to ceiling curtain would help. the cold air in the stair will mix with the apartment air and you will loose heat.
I second this. You’re heating an access stairway. If it has a window then you’re feeding a leaky outer wall. Not sure how much that translates directly into money lost which is really what you need to know before spending money on it. An old sheet or plastic tacked up would slow down the convection. Ultimately it may make it more comfortable if you’re getting a cold draft.
I would go with a heavy curtain that covers from the ceiling to the the floor with no gap.
I did something similar in a two story house where we don’t use the upstairs much. I just got a spring-loaded curtain rod & a simple 4’ wide drape & hung it across the staircase opening. Cost about $20 at KMart / Target. It paid for itself in the first week.
The OP will find it’s also a saver in the summer when the A/C’s cool air would otherwise be draining down into the stariwell.
And some floor to ceiling drapes are manufactured for this purpose, one side is a tight knit lining that is much more insulative than your cheaper big box offerings. Custom drape people may even put in a third layer of insulation.
you can buy layered material to make a thermal curtain. has silvered material to be on the warm side, an air filled insulating layer, a tight outside layer. fabric stores have it about 3/8 inch thick.
Black out curtains, designed to keep the light out, do a great job at keeping unwanted temps out too. They’re super thick and will keep you from losing heat.