When to use black-iron pipe

Q: I recently had a System 2000 boiler installed and noticed that all the threaded pipes coming off the unit are black iron. I was taught that black-iron pipe would rust if used for water lines. Does this mean I can run black-iron pipe anywhere in my house?

Chris Ermides, Beacon, NY

A: Bob Romano, service manager for Abbott & Mills Oil Heat in Newburgh, N.Y., replies: No, you can’t run black-iron pipe just anywhere in the house. Black-iron pipe is OK for gas lines and for closed-loop hydronic- and steam-heat systems because oxygen isn’t regularly introduced into the loop. The oxygen in water is what actually rusts the pipe. Stick to copper pipe or PEX tubing for use in your home’s potable-water lines.

From Fine Homebuilding 202, pp. 86 March 5, 2009