Galvanized Pipe in a Stove
This article from http://donkey32.proboards.com/thread/373/afraid-galvanized-pipe-anyways indicates that it's ok to use galvanized pipe inside a stove:
"I read a recent post which mentioned galvanized pipe and toxicity and realized this is a persistent myth in stove circles. I have a background as a chemist, my work includes machining and fabricating, and I think I know enough about galvanized to ease some fears and help dispel the myth.
First, galvanized does not give off 'cyanide fumes'. It DOES give off zinc oxide fumes, which can cause metal fume fever. Metal fume fever is an immune-response condition that goes away in a day or two as your body absorbs the zinc. It's rotten, much like the flu, but it is rarely fatal, usually only when the exposure is extreme and the person has a pre-existing lung condition. It happens to welders all the time, almost considered to be a standard occupational hazard. Welders who work in a enclosed environment and don't wear protection develop resistance rapidly.
Second, galvanized steel rarely gets hot enough to create said fumes except under conditions of welding, grinding or casting. During a stove test, I managed to oxidize 4' of my galvanized flue (it was under a fume hood, just in case). White oxides formed on the pipe but none was released into the air as fume. The fume is extremely visible when welding on galvanized material, as thick white smoke.
Zinc boils at 907C, ZnO at 2360C, and rapid oxidation occurs at much lower temperatures near the melting point of zinc (420C). Once the zinc has been converted to oxide, it is safe. Your stove will never reach 2360C without forced air or oxy mix. I personally use a fully oxidized white zinc-coated elbow as part of a stove I operate indoors, and it is completely inert. I have never experienced metal fume fever myself as I always am sure to have good ventilation and a respirator if I weld galvanized material.
I think galvanized is actually a better material for heat risers if you wish to use thin steel. The layer of zinc oxide will help protect the steel from oxygen and heat damage, I always use galvanized for heat risers in my small stoves and it seems to hold up very well. I always fire them gently at first to oxidize the zinc rather than melt it into a pool at the bottom of the riser. Any oxide fumes will find their way out the flue and not into anyone's lungs.
Finally, galvanized steel is commonly used, within code, as an exhaust duct for gas appliances (go look at your hot water tank or furnace) and even to BUILD WOOD STOVES! Ex. www.rileystove.com/products/stoves/riley/flap-jack.html is constructed with 18ga galvanized steel! No Riley customers have died yet!
Of course I'm open to any anecdotes of people who have gotten sick from galvanized stovepipe, so feel free to let me know if you or anyone you know has gotten sick."