If you own a home built prior to 1970, don't be alarmed by the following as it doesn't apply.
"Galvanized pipe should not be used", I'll bet you see that in a few of my posts. I figured I would tell you why. Since the '70s, a lot of our plumbing parts are coming from overseas, China, India, Singapore etc. In spite of industry and customer standards, for the most part it is now the worst quality plumbing material I have ever seen. A list of reasons it is a poor choice.
If you do use it, everything needs to be galvanized and or isolated.
Unless it is pre '70s or spec pipe, DO NOT USE ON STEAM! It will burst.
If you use one piece of galvanized in your system, it needs to be isolated or you subject your system to two forms of corrosion. One is Galvanic action which is caused by dissimilar metals.
If there is an electrical potential present you are subject to electrolysis and in this case, zinc is not the sacrificial lamb (unless your plumbing is in saltwater at about 50,000 PPM). Your boiler and plumbing are.
Galvanized found in hardware stores is most often hot dipped in zinc instead of plated. Again, poor quality control and a really bad product. This stuff is the worst thing you can use. The dipped zinc can fall off and jam pumps and valves.
I am not sure what causes it, but I know copper does poorly when galvanized is present. Lots of pinholes.
I don't recommend it for stovepipe either, when it overheats the galvanized is gone, where it goes I do not know.