Chmney cap condenses soot and drips

[ccaissie113]

Newbie here. My friend has always wanted chimney caps on his two chimneys, so I built two out of heavy gauge steel and heavy angle, and mounted them. Within a month he noted that creosote was condensing and dripping down his nice metal roof.

These caps have a roof design, are about 16" x 30" and weigh about 65#. one of them spans two flues. The roof sits 5" above the base, and i wonder if increasing the height of the risers would somehow keep this from happening?
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Any ideas?

 

[begreen]

It's inevitable as unburnt wood gases hit a cold plate of steel or stone that they will condense as creosote. The shed roof will cause this to drop to either side.

 

[ccaissie113]

So, that's the case with all caps? They all condense and drip? YUK.

Increasing the height of the roof ? how about inverting the roof so it condenses and then runs down into the flue? Crazy enough to work?

 

[begreen]

Raising it will help but not eliminate the issue. More efficient burning can reduce this but water vapor and volatiles are a byproduct of wood combustion. Most caps of this design are flat roofed, using stainless steel to reduce and slow down corrosion.

Understanding Chimney Caps

Mason Mark McCullough teaches host Kevin O’Connor about chimney caps, including what they do, how they work, and how to install them.

www.thisoldhouse.com

 

[gthomas785]

Tell him he needs to burn drier wood.
Yes, an inverted baffle inside guiding the drips down into the flue might help a bit as well.

 

[ccaissie113]

Flat roof...good idea. He gave me a cap with the peaked roof from another source, so I modeled it after that.

I could cut out the middle of the roof and weld in a flat section....yes, I have seen images of flattish caps with just the outer edge pitched down...
Thanks, great forum and members....

 

[kborndale]

Tell him he needs to burn drier wood.
Yes, an inverted baffle inside guiding the drips down into the flue might help a bit as well.

This I don't understand, why would you want to put the creosote back in the chimney? That's just more fuel for a chimney fire.

 

[gthomas785]

This I don't understand, why would you want to put the creosote back in the chimney? That's just more fuel for a chimney fire.

Ideally it would run back down into the stove, same reason you put all your pipe joints pointing down.
Just based on surface area, the amount condensing on the cap is presumably small compared to what is already accumulating on the walls of the flue.

 

[ccaissie113]

We are callng it creosote but it is just 99% sooty condensate water that's causing the drips and the stains. After 40 years of no caps, suddenly he has to have them.

 

[kborndale]

We are callng it creosote but it is just 99% sooty condensate water that's causing the drips and the stains. After 40 years of no caps, suddenly he has to have them.

What do you think creosote is? It is condensate.

 

[ccaissie113]

I consider creosote to be a baked polymerized mass of tars and other unburned volatiles. Although I have played some chemical engineering positions, I'm not a chemist. Creosote is a gereral term for "that black stuff"...but it could refer to the crust in your chimney or the stinky, sticky stuff you get on your sneakers when you walk on railroad ties in the sun.

 

[stoveliker]

When the water evaporates that is the resulting coating

Different kinds exist, tarry goey, or crispier.

 

[ccaissie113]

I knew that when I joined this forum it could become very informative. Not only can I rebuild the chimney caps but I will never look at "chimney drippins" the same way again. 8^)

 

[gthomas785]

I consider creosote to be a baked polymerized mass of tars and other unburned volatiles. Although I have played some chemical engineering positions, I'm not a chemist. Creosote is a gereral term for "that black stuff"...but it could refer to the crust in your chimney or the stinky, sticky stuff you get on your sneakers when you walk on railroad ties in the sun.

The stuff dripping from the caps is creosote, that's not really in question. The question is where does it end up. Once it condenses on the cap it can either go on the roof, or it can go down the chimney. Or it could be not created in the first place.

 

[ccaissie113]

Really the question is what to do about the chimney cap. Here in my neighborhood of Maine where we usually harvest ur own wood by availability, we also are subject to variabilities of atmospheric conditions during the season. Perfectly dry wood is not guaranteed, and I don't see advising the client that he now has to confirm that his wood is of such and such a purity.

So on to other solutions. Great forum.