Replace insulation inside heater column.

Thanks for the link. The insulation is available at any home improvement center. From the video it looks like it's standard unfaced R-13 insulation at about $22 a roll. Unfortunately at least at my HD they only sell R-13 faced (with paper backing) and unfaced is special order. If that's all you can get though, it's easy enough to peel the backing off the insulation before use. If you own a house you can just roll the remainder of the insulation out in the attic.