Chimney Caps

Chimney Caps and Dissimilar Metal Reactions

Tuesday, May 26, 2009 Posted by Stephanie H.

Is it possible to turn your chimney and chimney cap into a battery? Well, not really, but in a way you can inadvertently create conditions on your chimney top similar to those inside of a battery. I can best explain by first describing the basic chemical principals of a battery.

In 1800, Allasandro Volta created a basic battery by layering two dissimilar metals - Zinc and Silver - with blotting paper soaked in salt water. Most metals are electrically conductive, however, they all differ in their conductivity. If you place two metals next to each other you'll see very little happen. But, if you place a conductive medium between the two metals, like blotter paper soaked in salt water, then electrons will freely flow between the two dissimilar metals. This happens because one is less resistant to the flow of electrons and as soon as a port or door is opened between the two metals, electrons begin to flow freely from one metal to the other provided that the circuit between the two metals is completed.

Here is a how a simple voltaic pile is created. Place a silver plate on the bottom, then salt soaked bloater paper, then a copper plate. Repeating increases the voltage. You complete the circuit by running a wire from the very top plate to the bottom plate. The most complex of batteries all run off this simple basic design. After a while, the ions in the salted paper are used up and the battery "dies".

Now here is how this relates to a chimney top. Lets say you buy a beautiful copper chimney pot and decide to attach it to your galvanized chimney cover or chase cover. This is a common use of the increasingly popular European style chimney caps. This would not be a problem unless of course some kind of solutionChase_Covers with charged ions simultaneously touches both metals. Rain water is the perfect solution for this reaction. The many contacts between the two metals create both positive and negative channels for electron flow and you have in essence turned your chimney top into a voltaic pile. Eventually this will result in the premature degradation of both metals and the areas of contact will quickly corrode. Eventually the contacts will "burn away" and nothing but gravity will hold the copper pot to your galvanized chase cover. It will only be a matter of time before your copper pot ends up in your neighbors yard as a result of a stiff wind. This of course will happen long after water has had a chance to flow freely into the corroded chase and infiltrate your living space.

Here's what you can do to avoid this problem. Insulate the connections with some non conductive material like butyl stripping or neoprene washers. Better yet, eliminate the possibility altogether by replacing the galvanized chase with a copper chase.

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