Aluminum and copper

Mark Custis

A/C units. They live outside in the rain?

Al Letellier_21

aluminum and copper

Here is a new one on me: I recently have joined a Statewide association of professional home inspectors as part of my consulting business, and have had the opportunity to speak to them a couple of times on inspecting procedures for plumbing and heating, and this question came up. "With the advent of new processes for treating wood, copper is used by some manufacturer in place of arsenic as in the old pressure treated wood. As a result, aluminum flashing cannot be used as electrolysis will take place. If these dissimilar metals cause corrosion, why is it that aluminum fins on copper baseboard don't cause corrosion and leaks?"
I think I know the answer, but I would like to throw this one out to the guys on the Wall for your thoughts.
Thanks in advance for your input.

Andrew Hagen_2

Galvanic Corrosion

Water must be present for the corrosion to occur. The fins on baseboard are dry so there is no worry.

Andrew Hagen_2

Fins

Galvanic corrosion could occur in that situation. I suppose they assume that the fins are only wet intermittently and weigh the cost of materials against the time it takes for the unit to corrode.

The electrolyte closes the circuit. If it is just a dry connection between aluminum and copper, it's a battery with nothing connected.

Unknown

Rain

being mineral free is a poor conductor or electrolyte. This is why we dont get zapped touching a wet electric pole in a rainstorm

Al Letellier_21

aluminum and copperq

Thanks for the responses, fellow wallies....I felt that moisture was the answer but don't recall ever seeing it written anywhere.