Any time the vents are blocked or restricted in some way your furnace has to work that much harder to pull in the cool air from the room.
Can you paint air return vents.
I would just clean them really well and then look for the spray paint that s meant for plastic to be sure it will really stick.
Probably will require 2 coats.
Finish the grilles using the appropriate application technique or the paint may sag.
Painting your air vents to match your wall color makes them blend in with the wall leaving your furniture or artwork as the focal point of the room.
So if you are looking to do some simple upgrades clean off those vent covers and give them a coat of spray paint.
Spray the vent with a metal primer.
Or have you ever spray painted your vent covers.
Head outside to your driveway or garage door open and pop the vent covers in a cardboard box to contain the over spray.
It will really make your vents look so clean and fresh instantly.
Be sure to turn the vent cover over so you can paint both sides.
This is a great upgrade project to do if you are planning on selling your home too to make it more appealing to buyers.
I agree with painting them.
Once the return grilles are primed they will accept paint.
Spray the vent in a well ventilated area.
Paint will off gas and that does bother certain people and in reality isnt good for anyone.
Brush paint the vents after they air dry when the paint has dried reinstall.
However you can also purchase a decorative air vent that matches the design aesthetic of the room.
In most homes what seems to be typical is to paint the vent with a regular paint brush.
Condition the grilles with a special etching primer formulated with an acid base.
Carefully wash the vents and rough them with steel wool or a scotch brite so your paint will adhere.
Air return grilles are metallic a characteristic that leaves them less suited for paint than porous drywall.
So you ll be fine.
Remove them from the wall to paint the wall.
Give the spray paint can a good shake then use even strokes to apply the paint.
The problem with this method is that the paint tends to ooze through the holes which leads to a partial blockage.
Do you have some vent covers who could need some updating.
You could definitely paint plastic vents.
So in essence its no worse to paint the inside of that return as it is to paint the house.
This is the best design decision.