copper chimney cap and galvanic corrosion

[robman]

Hi My woodstove in the alcove is complete and beautiful. Thanks again for all of the help with design and safety issues. I am now reroofing the house (they went hand in hand) and will be buying a chimney cap. The chimney is actually a steel framed chase with durock exterior and has two flues coming out the top (the kitchen 6" vent and the 8" metalbestos insulated flue) and they are about 4.5" apart, which does not allow for conventional rain collars. I am going to cover the durock in a clinker brick veneer and will need a cover for the chase. As the home is a 1910 craftsman, I figure copper would look better than stainless but am worried about galvanic corrosion with the copper and galvanized ventpipe or raincaps. I will probably have collars put on the copper chase cover but am still worried about what to do to avoid the galvanic reaction. Also, when looking at Rockford and others' descriptions of sending measurements, it appears that they want the holes about .5" larger than diameter of pipe/flue and I worry that caulking will fail in that large a gap (and imagine backer rod cannot be used touching insulated metalbestos). With a collar on a chase cover, is there still a raincap and are those done in copper too? Any recommendations/ideas/suggestions are greatly appreciated and again thanks for all the help getting to this point.

 

[brenndatomu]

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Use this Flex Liner Deluxe Terra-Cotta Top Plate in order to mount the Top Plate to the existing Terra-Cotta flue. This Top Plate includes a detachable sing

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Multi Flue Chimney Cap - Chimney Liner Depot

These caps are made in our sheet metal factory. They are high quality, built to last. Our Multi Flue Chimney Caps are made from high quality 304L stainless

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[begreen]

I'd go with the stainless cap and paint it. The holes should have a raised rim to keep splashing out and then there needs to be a storm collar on each pipe. You may need to trim the storm collars back where they touch of put one slightly higher or move the kitchen vent pipe more outboard.

cap with rim

 

[robman]

Thanks again Begreen (you were very helpful on the alcove design part). I was hoping to be able to use copper for the looks. Also, the roof is pretty steep for an older mortal like myself (8:12) so I would prefer something maintenance free. I have seen ads for powdercoating stainless, Maybe I'll go that route. I was planning on using the rimmed cover just wasn't sure if you still use normal storm collar (galvanized resting on copper would be a problem.)

Thanks again

Rob

 

[begreen]

Personally, trouble and maintenance-free is the highest priority.

I painted the stainless steel flashing on our patio 17 yrs ago and have not touched it since. A good paint job will last a long time if properly prepped. I steel wooled the surface first, then wiped it down with alcohol, then roller painted with a Rustoleum paint. It still looks good with no chipping or flaking. Rustoleum makes all sorts of colored metallic paints including aged copper. At that high up, you will be the only one who knows it's stainless underneath.

 

[robman]

Thanks Begreen
Are there any fabricators that you'd recommend and are there different qualities of stainless that will deal better with rain etc? Also a recommendation on gauge?
Thanks again,
Rob

 

[Eman85]

you mention the hole being .5" bigger than the diameter of the pipe. That means .250 all around not a .500 gap.

 

[robman]

Thanks. I may need clarification here--do I add .25" to the radius or diameter? I think I was thinking .5" to diameter
Thanks

Rob

 

[begreen]

Thanks Begreen
Are there any fabricators that you'd recommend and are there different qualities of stainless that will deal better with rain etc? Also a recommendation on gauge?
Thanks again,
Rob

Rockford does custom stainless or copper covers. A good local metal shop should also be able to if given good drawings for the fabrication.

Chimney Chase Covers in Copper or Stainless Steel

Our high-quality and custom-made chimney chase covers are available in copper or stainless steel! Increase the safety, beauty and value of your home.

www.rockfordchimneysupply.com

 

[Eman85]

Thanks. I may need clarification here--do I add .25" to the radius or diameter? I think I was thinking .5" to diameter
Thanks

Rob

If the pipe is say 8" OD then the hole would be 8.5"ID when you put the 8" pipe in an 8.5" hole there's .250 gap all around unless you put it off center then you would have .50 on one side and zero on the other.