GARN - dissimilar metals - air intake

[Ecky]

With the GARN you get a galvanized reducer and hood for the combustion air intake. Could one use black stove pipe in-between to extend the intake to outside the building or would there be a problem with dissimilar metals? Or should I limit my extension to galvanized pipe? I am assuming dissimilar metals is only a problem when water is involved.

Comments?

 

[Jim K in PA]

With the GARN you get a galvanized reducer and hood for the combustion air intake. Could one use black stove pipe in-between to extend the intake to outside the building or would there be a problem with dissimilar metals? Or should I limit my extension to galvanized pipe? I am assuming dissimilar metals is only a problem when water is involved.

Comments?

Galvanized steel and painted steel are not "dissimilar" metals. You can interchange them without worry about galvanic corrosion. However, the black pipe is typically heavier gauge than necessary for the intake pipe, and is also more expensive.

 

[Ecky]

Thanks Jim. Why does GARN specify NOT to connect galvanized pipe directly to the GARN but rather to use black steel for at least 6'? As to the black stove pipe - it will actually work out cheaper for me since I can get the exact length I need with black stove pipe but would have to buy extra galvanized or aluminum intake duct pipe.