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

[Aaron FIsher]

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:

And, here's a pic of the enclosure back on the ground: 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?

[Aaron FIsher]

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:

And, the things (spark arrestors?) it's "protecting" on the affected chimney:

[Aaron FIsher]

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):

And, here is a picture of the affected chimney, sans steel enclosure: And, here is a picture of the enclosure on the ground: Here is a side view showing construction details of the enclosure: What else by way of information can I give you guys to help me figure out my next step?

[Aaron FIsher]

Amazing! I didn't even 'notice' those 'vents' on the bottom!

Interesting. I'm not sure 'how' to do that, but I do agree.

I was thinking more about BRACING the heck out of a new one. And fabricating it on the ground, and assembling on the roof.

Of course, the problem is the chimney is something like six feet tall on the short end and something like 7 or 8 feet tall on the long (downslope) end, so, getting on top of it is problematic.

But, there must be a way to do this!

Anyone know of a DIY?

[chaniarts]

when you get it fabricated, you can specify not only the dimensions, but how much each side bows out as long as each side is straight at the bottom (hint: each side will be a section of a cone). also, how it attaches to the chimney will be a critical measurement unless you want to redo that also.

well, yes. you can put braces on the top and bottom going across between the stacks. you'd have to make good measurements of the top for someone to build this for you. i'd get them to use pretty heavy braces.

got a friend with a crane? you might try calling places that replace a/c units. in my area, most a/c units are on the roof, and they just crane off the old one and lift on the new one. takes about 20 minutes once they're all set up. it might cost you some for crane rental time.

you might ask on rec.crafts.metalworking. at the least, you're going to need some pretty heavy duty tools: metal brake, shears, welding and/or drilling and bolting it together, etc. it's going to be heavy too. this isn't a typical diy job.

in my area, they do this with either sheet metal, like yours, or by building a metal rod frame, tying on a heavy chickenwire or expanded metal sheet, and doing a stucco job over that in place.

[Aaron FIsher]

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'?

[Aaron FIsher]

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):

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.

[chaniarts]

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 :)

[Aaron FIsher]

Expanded metal?

[hrhofmann]

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.

[mm]

As you suspect, they are parts of rockets. Civil Defenese workers and survivalists often included special preparations in their homes for times of unrest. The exhaust gases from the three things you mention are not sufficient to ignite the rocket engines until their ignition has been enabled. He must have left instructions to do that, right?

If not, try

.

On second look, those are chimney caps. What you took off is just a cabinet, to cover from view your ramshackle flues** and non-matching chimney caps.

**Especally the middle one.

I'm not sure but I would ask someone who knows more if the cover, given how high it is compared to the chimneys, reduces chimney draw.

I guess if the flue is hot the chimney draw is mostly dependant on the height. Maybe I'm confusing it with turbine attic exhaust fans, which have to have a breeze to work, but before I built another decorative cover, I'd check with a chimney company. Here we have a couple chimeny sweeps who expanded to all aspects of chimneys (plus another one who never expanded and low-balls and then tries to sell unneeded $300 pipes for $700 dollars, but that's another story.)

[mm]

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.

[mm]

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.

[mm]

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.

[mm]

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.

[Aaron FIsher]

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.)