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What metal is best for chimney cap
construction? |
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. |
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. |
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. |
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. |
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
hardners 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! |
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. |