I think I understand what she is wanting to do. If she has a Jenn Air like mine, it has a center down draft to the vent outside and cold air does come back thru it in the winter time. If she laid the top over the vent only it would help and wouldn't be touching any burners or cook top. I have used a manilla folder over the filter down in the down draft in the winter, but you must remember to take it out before you turn on the fan to take the cooking odors and grease out of the air while cooking. It doesn't touch the burners anyway shape or form, nor is it close to any of them. It lays on a metal filter that catches the grease etc. If you don't take it out when you turn the fan on, it doesn't pull anything out and will eventually burn your fan motor out. If you closed the vent from the outside, you couldn't use your fan to take the odors etc., out.