Furnace/Boiler plumbing - black pipe vs. copper

Dear Readers,
The supply/return pipes that come out of my furnace (I've learned not to call it a boiler) are threaded black pipe. Only after the circulators and expansion tank are they changed to copper. I assume this is to help bear the weight of these pieces of equipment on the line. Am I correct? Or is it that copper pipe cannot be within a certain distance to the furnace due to heat or possibility of galvanic action or some other reasons? Any ideas?
Thank you. Regards, Anthony
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On Nov 5, 10:44 pm, snipped-for-privacy@yahoo.com wrote:

1) Why are you calling your boiler a furnace? 2) I have seen boilers completely plumbed with copper, completely plumbed with black pipe, or a mixture of both. Your install probably just reflects the personal preferences of the installer.
JK
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