does anyone know what grade stainless is used in the secondary air tubes on new stoves, eg. 304 etc. would like to mod a boiler in the future. thanks.
stainless steel grade
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I would think 321 as it is the most heat resistant and what I would use if modding. Not sure though.
321 would certainly not be bad, though I don't know that it is so critical I'd go out and spec an actual grade. We're not talking jet engine parts here...just a tube which carries air and needs to hold it's own weight. When I did my retrofit, I grabbed an old stainless steel butcher table leg from the scrap yard... most likely a 304/316 grade and it's been doing fine for many years. Most people seem to report carbon steel tubes lasting a dozen years or so. Any stainless is an upgrade and generally lasts a lifetime. After that...who cares!
I'm right there with you on scrounging. I do it all the time and would also do it in this situation too. I was thinking about it from the perspective of say uppipes on a diesel truck which need to hold pressure. Air tubes in a stove don't need to hold pressure so the carbon steel sounds like an excellent choice for the price.
thanks for the replies will most likely use steel pipe as it is most common and fittings are easy to get as well.
Many have gone the steel pipe route... easy to get a hold of, standard fittings as you mention, and easy to replace if needed.
I don't know how much difference overall there is, but it seems for top notch performance, you want the pipe material to be fairly thin so it heats quickly and transfers max heat to the incoming secondary air. Under 'proper' operation, it's very easy to get the tubes glowing hot as well. This is where stainless becomes optimal because even a thin stainless tube can take glowing orange heat and show virtually no deterioration.
Here is a thread with pics of my burn tubes:
https://www.hearth.com/talk/threads/burnin-orange-tonight.106714/
I don't know how much difference overall there is, but it seems for top notch performance, you want the pipe material to be fairly thin so it heats quickly and transfers max heat to the incoming secondary air. Under 'proper' operation, it's very easy to get the tubes glowing hot as well. This is where stainless becomes optimal because even a thin stainless tube can take glowing orange heat and show virtually no deterioration.
Here is a thread with pics of my burn tubes:
https://www.hearth.com/talk/threads/burnin-orange-tonight.106714/
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