Magnets and painter’s plastic—now that’s clever. I’ve only ever used the sticky vent covers, and yeah, the residue is a nightmare. I get the appeal of magnets since you can just peel them off when you’re done, no scraping required. The only hiccup I ran into with magnets was in my old house where some of the vents were aluminum, not steel, so the magnets just slid right off. Ended up taping the edges anyway, which sort of defeated the purpose.
If you’re prepping for window installs, I’ve found that covering vents is just one part of keeping dust from spreading everywhere. I usually go step-by-step: first, move furniture away from windows and cover it with old sheets (plastic gets slippery), then I tape up doorways with plastic drop cloths to keep dust from drifting into other rooms. For the vents, lately I’ve been using painter’s tape to secure a doubled-up layer of lightweight fabric (like an old pillowcase) over each register. That way air can still flow a bit if needed, but it catches most of the dust and there’s zero sticky mess after.
Curious if anyone else has tried something like that—using fabric instead of plastic or stick-on covers? Wondering if it makes much difference in how much debris sneaks through. Also, has anyone had issues with airflow or HVAC performance when covering vents during reno work? I’m always a little paranoid about blocking things too tightly and messing up the system...