I think you can get them at Costco for about $60.00. Or an easier way is to just grab each header pipe. If it melts your skin, it's just right!
But seriously, just fill a squirt bottle with some water and shoot a dab on each pipe. The "sizzling" should be the same from each one. Just don't soak them. A little squirt will tell you what you need to know without risking a crack in the system.
Tom