Is a 3-foot tall sheet steel chimney cap 'functional' or 'aesthetic' ?

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I hate that word SHOULD. The OP's statement sounds like the chimney is high enough. But it could also be higher than necessary, inviting problems. Check with local codes. Usenet is a good thing, but it's like asking the weather tomorrow. I can say what it's going to be HERE, but everyone doesn't live HERE. So, start at the local level, find out the facts, and then build to comply.
When dealing with height, any increase increases the leverage put on it by wind.
Steve
Heart surgery pending? www.cabgbypasssurgery.com
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I sounds like the chimney surround is higher than the individual chiumney stacks from the individual units. A photo of that's on the roof now, and a photo of what was removed would sure help!!!!
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On Thu, 07 Apr 2011 08:09:34 -0700, hr(bob) snipped-for-privacy@att.net wrote:

I 'should' have taken a picture of the enclosure BEFORE I took it down, but, alas, I hadn't thought of that ahead of time. :(
But, here is a picture I took today of the 'other' chimney, which has what appears to be an identical chimney enclosure (purpose unknown):
http://www.upload3r.com/serve/080411/1302294051.jpg
And, here is a picture of the affected chimney, sans steel enclosure:
http://www.upload3r.com/serve/080411/1302291372.jpg
And, here is a picture of the enclosure on the ground:
http://www.upload3r.com/serve/080411/1302294453.jpg
Here is a side view showing construction details of the enclosure:
http://www.upload3r.com/serve/080411/1302295784.jpg
What else by way of information can I give you guys to help me figure out my next step?
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On Fri, 08 Apr 2011 15:36:46 -0700, Smitty Two wrote:

Ah. Good question.
I don't have a picture of that (I'd have to crack a few more roof tiles to do that!) but the chimney is totally 'capped' (if I understand you).
By that I mean, if you removed those three (spark arrestors?) from the chimney, all you'd have on the horizontal part are the three holes where they came out of the otherwise concrete flat top of the chimney.
Is 'that' what you mean by functionally 'capped'?
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Smitty Two wrote:

if that's correct, then what about making this using expanded metal rather than sheet metal? that would reduce the wind load a lot, but still hide the stacks. it might whistle a lot though :)
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On Fri, 08 Apr 2011 16:00:28 -0700, chaniarts wrote:

Expanded metal?
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I vote for purely aesthetic. The three stacks are ugly as sin, with the surround the chimney is only regular ugly. A new surround out of aluminum would get my vote for replacement materialss. There is nothing wrong with making use of pop rivets to hold the surround together, as long as it is sturdily constructed. You might consider pop riveting the new surround to the lower base unit to help strengthen the new unit. You also could do a lot on interior bracing of the new surround using aluminum angles and rods. The only thing that would be visible on the outside would be the rivets, and from street level I can't believe that would be objectionable.
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On Sat, 9 Apr 2011 00:13:43 +0000 (UTC), Aaron FIsher

Expanded metal is sheet metal with a lot of cuts in it, in alternating rows offset by half a cycle, and then pulled apart somehow so that each cut becomes a diamond shaped hole. A narrow diamond, compared to its height, compared to a diamond on a playing card.
It's used various places, maybe the grill inside a charcoal stove; definitely the bottom of most cargo carriers that fit into trailer hitches and are 20" front to back and 5 feet wide. Maybe even iirc the seat of some outdoor wrought iron furniture, above which goes an upholestered cushion.
That's why it might well whistle. Probably would at some wind speeds.
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wrote:

Not sheet metal I mean, something thicker than that.
The steel version is pretty heavy. Do they make it in aluminum?
YOu can see through it some, and but maybe from the ground they won't be able to see the ugly stuff underneat.

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On Fri, 8 Apr 2011 22:42:47 +0000 (UTC), Aaron FIsher

I get it now. No, those are chimey caps. They also function as spark arrestors, but they are called chimney caps.

No, you'd have the pipes that go into the caps. The chimneys. All three pipes are visible in the picture. I don't like to fiddle with mine but aiui they clip onto the chimneys with a built-in clip. My first experience with mine was when it blew off, after the clips failed, so that's why I don't try to take off the replacement, just to see how it works.

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On Sat, 09 Apr 2011 00:30:42 -0400, mm wrote:

OK. I'll call them 'chimney caps' from now on.

Ah. I see. OK. I have three chimneys, with three chimney caps, and an enclosure for aesthetics. Is that right?

One of my chimney caps is tilted slightly from when I took off the heavy steel enclosure. I can 'clip' it back on ... but somehow I have to get from the roof to the top of the chimney.
I can try a stepladder - but those tiles. Oh those tiles. Is there a good technique for putting a ladder on the chimney (30 feet up in the air) without breaking the tiles? (I'll probably use a board under the stepladder legs; but that might be slippery.)
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On Fri, 08 Apr 2011 15:36:46 -0700, Smitty Two wrote:

There is a short length of what appears to be just under five inches of light "angle iron" at each corner of the steel enclosure.
Here is a picture from the side that shows the remaining three corner attachments (the fourth came down with the enclosure):
http://www.upload3r.com/serve/080411/1302302091.jpg
The four 'corners' are NOT made of 'real' angle iron; they're definitely made of the same sheet steel that the enclosure is made out of. It's bent in the shape of an angle, and then folded over partway where the three screws are screwed into the chimney and into the enclosure.
Two of the three screws on each of the two edges of the V-shaped corner piece are screwed with a 5/8" long screw into the chimney and the third screw is screwed into the sheet metal holding it onto the corner piece.
All in all, it looks like a pretty flimsy support to me considering the side-of-a-barn profile to the wind.
Certainly I'd use more substantial corner supports & longer screws for the two bottom ones. And, instead of the same (sheet metal?) screws, I'd use a concrete screw (if that exists) for the bottom two screws holding the 'angle iron' to the chimney.
It's hard to explain, but the picture above should show it in situ.
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On Fri, 08 Apr 2011 15:36:46 -0700, Smitty Two

But it's not a cap, it's aa box. With no top, right? Now that I see it's tapered it looks a lot better, but still my previous doubts obtain. Go talk to the guy who owns the other chimney and ask him all about it. Find out why his didn't bend, if it thwarts the draft, and maybe he knows where it was made and you can get another there. Especially good if it is a stock item somewhere -- I doubt it, but ask.

The suspected fire arresters picture wouldn't work for me.

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On Thu, 07 Apr 2011 05:24:45 -0700, Steve B wrote:

Hi Steve, The one that was there must have been there a while (I have no idea how long though, as the house is 30 years old).
It's made out of sheet steel, galvanized probably as there is no rust, and it is pretty darn heavy (at least while I was on the roof, on my tip toes, my arms over my head, trying to wrestle it off the chimney itself).
The chimney is way higher on the roof that you guys seem to intimate. It's at my eye level on the upslope and well over my head on the downslope side.
The winds here are easily 100mph with gusts that are higher, so, that's pretty much what killed the prior metal enclosure. It really needs to be braced better.
But, I can't possibly solve the problem until I figure out WHAT the roof enclosure's purpose is.
Here, again, is a picture of the enclosure on the other chimney:
http://www.upload3r.com/serve/080411/1302294051.jpg
And, the things (spark arrestors?) it's "protecting" on the affected chimney:
http://www.upload3r.com/serve/080411/1302291372.jpg
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On Thu, 07 Apr 2011 05:59:28 -0400, Ed Pawlowski wrote:

The 'bottom' of this enclosure (i.e., the top of the chimney) is 'way' higher than that!
While I'm on the downslope of the chimney, it's above my head just to the 'bottom' of the enclosure; and at the upslope roof side it's about at eye level to the top of the chimney (i.e., the bottom of the metal enclosure).
With those three 'spark arrestor?' things sticking out, I don't really think the enclosure is for fire purposes. I suspect there's some other intent.
Again, here's a pic with the enclosure removed:
http://www.upload3r.com/serve/080411/1302291372.jpg
And, here's a pic of the enclosure back on the ground:
http://www.upload3r.com/serve/080411/1302291053.jpg
What I'm thinking (hoping?) is I can pre-fabricate the 2.5 feet high by 5 feet long by 2 feet wide thing on the ground, and then assemble it up on the roof. Then I have to figure out how to brace it against 100mph winds.
Any ideas?
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On Wed, 06 Apr 2011 22:50:10 -0400, Ed Pawlowski wrote:

I don't think the enclosure is intended to make the chimney extend any farther than it already does because (a) the chimney is already over five feet above the roofline, and (b) the metal enclosure isn't any higher than the three 'spark arrestors?' on the top of the chimney anyway.
The roof is tile and the chimney is, what appears to be, concrete of some sort.
Here is a pic of the chimney that is intact:
http://www.upload3r.com/serve/080411/1302294051.jpg
And, the one where I had to take down the enclosure:
http://www.upload3r.com/serve/080411/1302291372.jpg
And, a side view of the destroyed enclosure (don't ask how I got it down all by myself):
http://www.upload3r.com/serve/080411/1302294453.jpg
What advice can you give me for replacing it?
What I'm thinking is to either leave it off (if it's not functional) or to assemble a new one on the roof.
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