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What
metal is best for chimney cap construction?
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Main
Factors: It is hard to find the best balance between style,
longevity, strength, and cost. These factors do not just naturally blend
together. We feel we have done well to reach the best balance possible.
(a) Chimney caps need to handle a great
deal of heat (unless the exhaust is just from
a natural gas heater). I have personally stoked up a wood stove
so hot the steel pipe was glowing orange and lit up the living room.
It was about 15 years ago and I was not trying to test this theory.
I was just burning some paper garbage. You can see these statistics
at a web site called
Online Metals.
Most metals handle high heat well, but if it has a zinc coating
for rust protection, or was soldered together, those metal coatings
melt at a very low temperature and will result in a serious failure
before long and cause rust stains.
(b) Thicker and heavier sheet metal
is most always best, so that it is strong and less prone to wind damage.
But that of coarse greatly increases the cost of the metal used and
the shipping charges. It also makes it harder to cut, drill, and bend,
so finding the best balance is important. That is why I use more internal
bracing, in stead of just thicker copper sheet metal than I already
use.
(c) The cost of the metal type is
a small consideration on your end for any custom work like this. Most
of the cost by far is the design and custom fabrication process with
shipping. A 500% increase in the metal cost would only have about 25%
increase in the total cost, so a better metal is by far your best value
any way you slice it. Anything less is a waste of money. These copper
chimney caps will normally increase the resale value of the house more
than the cost difference, so you can make a profit from using better
materials that will last.
(d) A long life metal that will stay
looking good decades later and need little to no maintenance is a much
better value, but even more so in just the extra cost of the labor to
replace cheaper units more often. Rust stains from common steel units
can be very unpleasant if the unit is not changed every 10 to 15 years.
A well made copper unit should last well over a century. That saves
you 7 or more replacement and installation cost alone.
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Steel
(very poor choice, yet most common):
Galvanized or high temperature painted steel is the most common
metal you will see. Mainly because it is so cheap, quick to spot weld
together, strong, and handles high temperatures well. Few homeowners
take the trouble to look into these details, so contractors will use
the cheapest materials they can get away with. In most States the contractor
is only required to provide a 1 year warranty. Steel cost less than
1/6th the cost of copper, but in the long run it actually costs far
more to the homeowner with the cost of fabrication and repeated installation
each decade or so. Then there is the cost of rust stain removal and
or repainting.
The galvanized steel cap shown here was less than 15 years old.
It was so rusty, pitted, and worn thin that we could crush it with our
bare hands like an aluminum pop can. You can see here dozens of daylight
pin-holes through the metal (we did not doctor that photo). Two
of the three bracing that held this hood up had disintegrated.
The strap clamp had disintegrated so badly that we were able to lift
it off the stainless steel chimney pipe it was attached to without loosening
the clamp. The worst part was how it left terrible rust streaks
down the sides of the stainless steel chimney pipe and on the roofing
that are now pretty well permanent (as seen here). I tried to use a
wire brush in it, but it did not seem to help.
The simple flat roof chimney cap most commonly seen is not
the type of chimney caps we make. Those are small generic size
caps that are mass-produced and sold in many hardware stores.
It is normally designed to bolt onto a flue liner, but most of the chimneys
we have seen do not have a flue liner tile protruding up over the bricks
to attach that specific type of cap to.
That type of cap may work on your chimney, but it's not very decorative.
It is fine for an inexpensive temporary solution. Steel can handle a
good deal of heat, with a melting temperature of 2,500 degrees F. Heat
and rain will dissolve the zinc galvanizing away. The zinc melts off
at only 787 degrees. Even though the high temperature paints can
handle more heat than a zinc coating, it is not much better, since it
is prone to suffer UV damage from the sun and oxidization. You
can see these statistics at a web site called
Online Metals.
If you let it go too long steel chimney caps will rust and make
unsightly permanent rust stains down the side of the chimney and on
the roofing shingles around it, that are near impossible to remove.
Eventually it will deteriorate so badly that it will literally fall
apart. If you factor in the labor cost of replacement each 10 to 15
years, spending $3,000 on a copper chimney cap is cheaper than getting
a small inexpensive $100 steel cap. Steel chimney caps are not
a good value for your dollar. Not when a copper chimney cap should
last well over 100 years, if built well.
Steel is good for repeat sales; due to it's planned obsolescence.
These are also the main reasons why we do not see more car bodies made
out of aluminum sheet metal, like with the Acura NSX sports car pictured
below.
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Aluminum
(good for low temp natural gas exhaust only):
Aluminum will take much more heat than a zinc coating
on steel; at 1,218 degrees F. But for use over a wood burning
chimney it can reach such temperatures that would warp the aluminum
sheet metal or worse. I have personally stoked a small wood stove
so hot that the black painted steel stove pipe was glowing orange, and
lit up the room. And aluminum pipe would have melted at that temperature.
If the chimney is only used for venting natural gas exhaust, thin aluminum
ducting is commonly used, since the heat requirements are so much less
and fairly consistent.Aluminum would also need to be very
well built and attached, since it is a lot softer metal and a lot lighter,
and therefore is more prone to wind damage. Aluminum is great for aircraft
construction where weight is very important, but it is not an asset
for a chimney cap.
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Brass (good)
Brass is
just copper with 30% zinc mixed
in to help reduce the cost, make it softer, and gives it that yellow
look. It will still tarnish and turn black with age with less of that
chalky green tarnishing. The zinc is a very soft metal, which makes
brass a softer sheet metal than copper, requiring a little thicker sheet
to have the same dent resistance; making it not really a cost savings. |
Stainless Steel (better):
This is a good strong high temperature metal, but it is just
as expensive as copper; costing 6 to 10 times more than just galvanized
steel. It may look good on a diner car, but one of the biggest
drawbacks to stainless steel is how it will stay bright and shinny,
will get dirty, and mildew on the North side (just
like in this photo taken on the Pacific Coast, over a church near Cannon
Beach, Oregon). It is easy enough to clean once you are able
to safely access it, but that can be enough of a hassle that just doesn't
happen.It is quick and easy to just spot-weld together, so
most shops will opt for stainless steel when forced to work with a rust
free metal. Like with copper, other shops will usually get very thin
sheets of stainless steel to to work with in order to help reduce the
cost and make it a lot easier to cut, bend, and drill. The thinness
of the metal will tend to show a lot of irregularities and buckles on
a flat surface. Hence the big 'X' bend you will commonly see in
these flat panels. Most people think it is a design feature, but that
actually has nothing to do with why they bend that 'X' through the metal
panel.
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Copper
(best):
Other than cost and tricky handling, there is little to no downside
to copper. Copper is the best value for the money, since copper is one
of the few metal meant to be seen in it's natural state or oxidization,
and is about the same cost as stainless steel. The fabrication
may cost a little more, since it is not as easy to work with. Copper
will tarnish to a nice satin brown within a few months of exposure to
the elements. The striated chalky green patina actually takes several
decades to form.
We only fabricate our custom copper work in 20oz
copper sheets or thicker, which is 125% thicker copper than the standard
16oz copper normally used in the roofing industry. Copper is a
heavy and sturdy metal that handles around 2,000 degrees F. It needs
no coatings over it for protection from the elements to burn off, bake
off from the Sun, or wear off over time from wind and rain. It
has a melting point about 700 degrees higher than aluminum.
Unlike most other shops, we go to the trouble
to rivet the overlapping seams together, since the melting point of
the lead type solder is far less than even aluminum and less than the
zinc coating on steel. It would be terrible if the cap were to
fall apart from the solder welds melting apart. We have seen plenty
of evidence of this happening. We have to design our chimney caps
to be strong enough for high winds, and not to leak, without the use
of solder or even caulk, and yet be easily removable for future cleaning
and servicing.
Fabricators who are more about mass production
do not like to work with copper, because it cannot just be quickly spot
welded together like steel and stainless steel. Handling is also
tricky, since finger prints will cause the copper to tarnish sooner
than the rest of the copper surface, making it spotty looking until
it evens out. So will wearing protective gloves while handling
bare copper, but most of it will have a clear plastic film over the
outside when you get it, that you simply peal off after installation.
New copper looks nice, but we have yet to find
a good method to keep it from tarnishing. Raw copper is actually
more pink, but most people see it as an orange'ish color, since it has
already has begun the tarnishing process by the time they see it just
from the humidity in the air, beginning it's process to turn brown.
Any clear coat applied over the copper surface can be a problem, since
it will not handle the heat well. Even without the heat issue,
the sun's UV rays and the elements will break the clear coat down before
long, causing unsightly peeling and a spotty tarnishing where it has
cracked and peeled off the copper surface.
Fortunately most people we have talked with seem
to love the natural aged striated tarnish look that real copper gets,
and some ask if we can pre-tarnish the copper here in our shop.
I explain how within a few months it will naturally tarnish, so it is
not worth the added cost, but it can be done before shipping by applying
an acid wash to pit the metal surface and cause this premature reaction.
Not well advised if I may say.
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Bronze
(excellent, but too hard to work with):
I have not seen a source for large sheets of bronze, because
it is not a malleable metal and therefore not good for sheet metal that
needs to be bent and shaped. It is made of 70% copper with a mix of
hardeners to make it stronger and more scratch resistant. |
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Titanium
(excellent, if you can afford it):
Other than the fact I have not seen this sheet metal available
because of such small demand, it would be horribly expensive and very
hard to work with. As an example: I jokingly say how I would be willing
to pay more for a titanium extension ladder to have a stronger lighter
ladder, but the $5k it would cost replacing it when it gets stolen would
be a real drag! I do have a titanium hammer and cats-paw that were about
4 times the cost of a normal steel tool of it's kind. They are great
tools and I feel well worth what I paid. Real Titanium is truly am amazing
metal, but they would have to be mass produced to be any where near
feasible. The head on the hammer is still nearly as smooth as when I
first got it. I am eager to see more products and tools made from this
metal, but not many contactors are willing to pay 3 to 4 times as much
for a tool, so few manufacturers are willing to make and market them.
You also will need to be careful not to get swindled with an inferior
grade or a complete substitute. Think of how many products are advertised
using the word platinum or turbo charged (LOL). Real platinum is more
expensive than gold for goodness sake!
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Silver
(well worth the brag points, if you can afford it):
Again I have not seen a source for large sheets of sterling silver,
or even pewter, because of the high cost and therefore low demand, but
that would be pretty cool. It would still tarnish and look much like
aged copper, unless you hired someone to polish it each year. I'm game
if cost is no object. |