Metalbestos SS exterior chimney too hot to touch.

[Tomm]

I have a 6" Metalbestos SS chimney, venting a Vermont Castings Resolute woodstove. The single wall, heavy guage, black pipe vents directly off the top of the stove and connects straight up and into the ceiling pass-through/thimble and directly into the insulated, double-wall Metalbestos SS chimney. The length of the double wall pipe is approximately 12', including the sections above the roof. The chimney has a cap. The chimney / stove installation was installed by me, ten years ago. Since I was a stickler for following 'the Code' and NFPA 211 (and was a NCSG Certified Chimney Sweep and Certified through WHERF) I am confident the installation is correct. During the 15 or so years I worked in the solid fuel / chimney industry, I never encountered the problem I am now going to describe. During some recent rain storms we encountered water dripping off the edge of the ceiling thimble and onto the stove. I checked the flashing (we have a very shallow pitched roof) and re-tarred the flashing. I removed the top two sections of chimney and, after laying them on the roof, noticed a 2" puddle of water drip out of the chimney section from somewhere. I suspect that water somehow leaked into the chimney and the insulation got wet. I put the chimney back together and started a small fire in the stove. After about 20 minutes, water started to drip from the same location on the ceiling thimble. When I went up on the roof and felt the exposed exterior portion of both Metalbestos SS chimney sections, they were too hot to touch. I am thinking that the water in the insulation (if that actually is the case) may me 'boiling off' and that is causing the chimney exterior to be so hot. I then let the stove go out and allowed the chimney to cool overnight. This afternoon I started another fire in the stove and re-checked the chimney. Again it was almost too hot to touch. Now when I say too hot to touch, I am thinking it is under 200 degrees because I can hold my hand on the chimney for a moment or two. It is not so hot that water sprayed on the outside steams, but it does evaporate quickly. My question is this, since I never had to clean a double wall chimney while it was in use, how hot should the exterior wall of a Metalbestos SS chimney be during normal woodstove operation? I suspect that the external temperature I am experiencing is not normal. If water did somehow seep into the chimney insulation, would the insulation distort, compact or shift to a point where hot spots would be created? Is it possible that the insulation would have migrated out of the chimney somehow? I see a paper-thin/thickness opening between the outside wall of the inner flue and the hole through which it passes. Would the insulation have migrated out of this tiny space over the past few years and created a loss of insulation. I don't believe that is the case hear, though, because there are not really hot 'spots', the entire sections feel hot.
Any thoughts, comments or suggestions would be appreciated. I am seriously considering replacing the chimney. I also plan to contact the manufacturere for their input. Might this be covered under their Warranty, perhaps? Be Safe, Tom

 

[KP Matt]

I'd have to say it's too hot.

If I recall correctly, I can keep my hand on my chimney indefinitely just above the attic insulation shield, even with a good fire going.

Water is a conductor, not an insulator, so it makes sense that it would get hot.

One problem with those Selkirk/Metalsbestos (I have Selkirk) is the open ends - I guess there's an advantage in that they can shed heat to other sections during a flare up, but they do seem open to the elements, and I don't find the way the sections connect very reassuring.

Maybe someone will have something to say about whether water degrades the insulation at all?

I would be wondering about how to make sure all the sections (four of them?) are completely dry... assuming you're confident you've dealt with the leak.

 

[webbie]

You should contact the technical people at the chimney maker....most have an email address or phone on their sites.

BUT, it is perfectly normal for the surface of class A chimney to exceed the temperatures which allow them to be touched. VASTLY.

As an example, they have to be 2" from wood - which is allowed to heat up to as high as 170 degrees or do - WAY hotter than you can touch. So if a surface 2" away can be 170, it would be fair to say that the pipe can easily hit temps of 250+ - almost an instant burn for the skin.

 

[KeithO]

Tomm: Whatever you do, you need to get the water out of the insulation. Water will attack silica based fiber if you give it enough time. Add in some CO2 and you have an acid. I would drill 2 or 3 small (1/8") holes in the OUTER tube as close to the bottom of each length as I could get. Any trapped liquid could then run out under gravity. With heating, it would allow steam out too. The worst thing that can happen if you don't provide ventilation is either splitting the outer seam or imploding the inner tube if you generate steam when in operation. I have seen it happen with mufflers that have 2 layer housings, get a little moisture between the layers and bam, you implode the inner wall and have a serious acoustic problem.

You may need to re-seal the very top connection and any other exposed joints where water can enter with silicone. That part of the chimney is more than likely cool enough for silicone to survive. Just remember that it is always a bad idea to try to seal anything completely. There is air in that insulation too, and it needs to expand and contract as the chimney temperature cycles. If you seal it up too tight, it will suck in air (and water) from the weakest spot it finds. Next cycle, you suck in more air and moisture. Soon you have a problem. Better let the thing breathe and if possible, allow anything that can get in to have a secue way of finding its way out too.

 

[Tomm]

I appreciate all the advice. I sent a couple emails to the manufacturer but have yet to receive a response. I'll forward on their information as soon as I get it! Thanks again.

 

[seaken]

Metalbestos has a great technical support staff. I haven't tried e-mail but we have always had good results over the phone.

If you purchased the chimney ten years ago it is probably the packed silicate insulation variety. There is a small gap between the inner pipe and the bottom cap and they used a thin fiber gasket to help keep the gap from leaking while loading and shipping. It was possible for that insulation to settle and allow "hot spots" but to my knowledge there has never been a problem as long as all the proper clearances were maintained and the proper supports and firestops/joist shields installed.

MB has since changed the formula of the insulation and now use an insulation that is more similar to the blanket type insulation used in other insulated chimneys. The old silica "dusty" stuff is no longer used in their consumer grade chimneys. Upgrading to the new pipes might be a good idea if you suspect the insulation has been compromised.

It is not unusual to have a hot outer casing, too hot to touch. Again, this is fine as long as all clearances and fittings are properly installed.

Water getting in between the inner and outer pipes is a bad thing and should be prevented. If the pipe has been invaded by water you must dry it out and prevent any further leaking. The pipes are designed with a "breathable" format and are not completely sealed. But they should "shed" water just like your flashing does. Look for any possible leaks on the exterior and seal them up with good clear 100% silicone.

Sean

 

[Tomm]

Thanks Sean.
I spoke with Karen at Selkirk (800-992-8368, ext 2212) and she was quite helpful. She mentioned that water could enter the chimney from the eight slits at the top of the chimney, immediately under the cap and/or possibly from a slight opening (had it been damaged iduring shipping) in the external vertical seam. She also mentioned that the exterior temperature of the pipe could be as high as 400 degrees (F) and still be in compliance with the safety/code requirements that specify a 2" minimum airspace to combustibles. This higher external temperature was achieved when they were putting, I believe she said, approximately 2200 degrees into the flue. I am certain that my external chimney temperature was no where near 400 degrees as I would have left my finger and palm prints fused to the chimney! Her recommendation was to ensure that the cap is covering the eight slits at the top of the chimney and, if it appears to be needed, silicone seal the vertical joints with hi-temp silicone. She said that I should NOT seal the horozontal joints together as this will be the avenue for the moisture to escape. I am burning the stove today and have noticed that the top section is no longer hot to the touch. The next section down is still hot, so I suspect that either the water that was in the top-most section has evaporated or drained down into the lower section due to gravity, or a combination of both! I am now wondering whether this has always happened at the beginning of each heating season, but I was never aware of it since I always cleaned cool/cold chimneys. That is except the one time I used a plastic/nylon brush in a clients hot masonry chimney and the brush shrunk and melted due to the high temperature remaining after a chimney fire! I know the chimney cap is on secure and covering the eight slits well. I think what I might do is let the chimney go this season without sealing the vertical joints (they seem perfectly intact and with no gaps or imperfections) and see if I have the same water issue next fall. If I do, then I will seal the vertical seams and see what that does. Although this was the first time we had the water dripping into the house from the thimble, Karen mentioned that the 'drippage' could also have just gone into the insulation and/or the flue without exhibiting itself externally.
Well, we shall see! By the way, is SNEWS Magazine and Chimney Topics Magazine (from Gelco) still out there? I got out of chimney restoration/repair/cleaning approximately fifteen years ago, but recall these two publications as fine trade journals. In fact I had written, and had published, a few articles and first hand experiences for SNEWS Magazine reference hidden dangers in newly constructed masonry chimneys, solid fuel installations and dangerously installed prefabricated fireplace/chimney installations. If anyone is interested in this information, let me know. If SNEWS is still around I am sure they should have back issues available. If SNEWS is no longer out there, I'll scan in my articles and forward them on to who ever might be interested.
Thanks again for everyones input.

Tom M

 

[n6crv]

Hello Tomn, I would kind of wonder whats going to happen if you let the fire go out and the chimney freezes? I would think that it might split the seem then. Hope all the water gets heated out by then.
Don

 

[seaken]

By the way, is SNEWS Magazine and Chimney Topics Magazine (from Gelco) still out there? I got out of chimney restoration/repair/cleaning approximately fifteen years ago, but recall these two publications as fine trade journals. In fact I had written, and had published, a few articles and first hand experiences for SNEWS Magazine reference hidden dangers in newly constructed masonry chimneys, solid fuel installations and dangerously installed prefabricated fireplace/chimney installations. If anyone is interested in this information, let me know. If SNEWS is still around I am sure they should have back issues available. If SNEWS is no longer out there, I'll scan in my articles and forward them on to who ever might be interested.
Thanks again for everyones input.

Tom M

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http://www.chimneys.com/