Elima-Draft 11"x11" Insulated Magnetic HVAC Vent Cover For ALUMINUM Vents Save up to 10% annually on your heating bills (Energy Star Home Rated) Keeps existing heat in where it belongs Eliminates cold drafts No tools required Fits ALUMINUM vent size: 11 x 11 (will fit slightly larger vents  ie: 11 1/4 x 11 1/4 as well)