I have two tubs and a tank on a deep bookcase (a temporary measure while I work on a custom enclosure) and when the room gets cold I throw a fleece blanket over it. It seems to do a good job of keeping the ambient temps up, though I haven't tried other fabrics to see if it makes a difference. I live in a basement studio where space heaters are remarkably ineffective, so its proven to be a good short-term fix.