Here's a link to a Thermometer that is for double-wall flue pipes like mine.......figure it's a good one?
(broken link removed to http://www.northlineexpress.com/itemdesc.asp?ic=5CN-3-39)
-Soupy1957
(broken link removed to http://www.northlineexpress.com/itemdesc.asp?ic=5CN-3-39)
-Soupy1957