I just got myself a super sucker forge hood and I’m loving it. I couldn’t find a 12” pipe but a friend of mine gave me some 13” that’s working really well. I’m concerned that the pipe might be galvanized. I’m not sure how to tell if it is for sure. If it is in fact galvanized will that be a problem? I know galvanized releases toxic fumes if it gets hot enough but will the chimney reach that high of a temperature? I don’t want to be breathing in toxic fumes. I’d like to know what folks think about this. 
Thanks in advance

We've had good discussions of this before. Here are some links to a couple of those:

• https://www.iforgeiron.com/topic/21002-galvanized-flue-pipe/
• https://www.iforgeiron.com/topic/31271-forge-chimney-questions/

The flue on my coal forge is galvanized pipe above a helium tank super-sucker, and I haven't noticed any fumes coming off the steel. However, I rarely use it these days, and even when I do, it's next to a wide-open double-width garage door.

It does look galvanized.

In general, it shouldnt get hot enough in that configuration to burn off the galvanized coating burning coal, coke or charcoal. 

It could possibly if you were burning a larger pile of wood or cardboard but that wouldn't be good or productive for your forge. 

 

I made a 14" x 14" by 4 ft. long that goes through the side of my shed . the chimney, galvanized air duct, it will be 2 ft. from the firepot and outside. I copied this setup from a picture of Hofi's setup. I don't know what material he used.

Here are images of a "Hofi Style Chimney" . Could be galvanized, could be aluminum.

I also had galvanized pipe for a chimney in the old smithy space, well ventilated but the forge stack never seemed to get hot enough to off gas the galvanized coating. It did get hot enough to melt off stickers about 2 feet up the pipe, but not higher. Anecdotal data points, but stickers are a cheap way to see how hot it's getting.

I'd be careful, keep an eye on the chimney, looking for any deterioration in it. And keep an eye out to scrounge some uncoated steel duct.

forgoing a chimney in the new smithy for now. Burning coke and lots of ventilation space in the half walled sheet metal building make a chimney seem unnecessary for now.