It's a panel building from the nineties. The draft used to be normal, but now it seems like the air isn't going anywhere. How can I tell if the ventilation is clogged or if it's already a defect in the building itself?
Checking draft is actually simple - a match and paper give you an answer in a second. But here's the thing: in '90s panel buildings, it's often not the grill itself that gets clogged, but the shaft section right behind it, and there's garbage stuck there like a solid plug - a match won't show you that. If the check says "there's draft," but smells and humidity still won't go away, call an inspector from your management company and ask them to clean out the internal part of the shaft - you can't get to it yourself, and it costs next to nothing compared to fixing water damage.
The simplest way is to hold a lit match or lighter up to the ventilation grate: if the flame tilts toward the opening, the draft is working. You can also hold a piece of paper up to the grate - it should get sucked in and stay there. If there's no reaction at all, the duct is probably clogged, and you'll need to call your building management to have it cleaned out; but if something's barely happening, the problem might be a clogged kitchen hood filter or closed windows (without fresh air coming in, the hood can't work properly).
In panel buildings from the nineties, the blockage often happens right at the shaft entrance - dust and even bird nests pile up there. Besides the standard checks (match, paper), try looking at the grate itself with a flashlight: if you see only a dark wall of dust instead of an opening, the clog is definitely the problem. To clean it, you can call your management company or hire a specialist - don't try poking around in there yourself, it's risky, you won't restore the draft afterward, and you'll just cause damage.
Did anything change in your apartment after the renovation - maybe you installed plastic windows or a new front door? People often forget that airtight windows and doors block natural air intake, and ventilation simply can't work properly without it.
If your windows are fine, then yeah, a match or piece of paper will help you see if there's any draft at all. But I'd also suggest opening the window at least a crack and doing the check again - the difference will be really noticeable. If draft appears when the window is open, then the problem is definitely with air intake, not a clogged duct.
If there's no draft even with the window open, then it's probably blocked. At that point you need to call your building management - they should clean out the shaft. In nineties panel buildings this is a common issue; dust, cobwebs, and sometimes bird nests accumulate in there over time. You can't fix it yourself.
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