OK to seal storm collar AND top of cone under it?

[BackwoodsVT]

Hey All,

I've read some comments about similar problems like this and thought I'd ask your advice on something I haven't read yet. I've got a square ceiling support box with double walled pipe going up into a small vented attic area and then up through my roof. Ever since it was installed a couple years ago, we'd get some rain dripping down from the corner of the support box whenever there was a heavy heavy rain. Eventually the top of the stove got pretty rusty so I decided to take care of it all this past weekend. Went to the wood stove store and got a couple cans of Stove Brite paint and some high temp silicone. I asked the installer there about what to look for when up on the roof and he said that, as long as the base of the cone looks like it was installed correctly (mostly exposed but shingles laying over the top edge), I should check under the storm collar and see if there is too much of a gap between the collar and the cone. He said there does need to be some airflow coming from under the cone, to allow the heat in the support box to escape.

Got up on the roof, removed the storm collar and, on one side of the cone, found a gap about 1/2 an inch wide. The pipe wasn't perfectly centered so it was almost touching on the other side. The installer had tried to seal up the gap but it was so wide, most of the sealant settled down into the opening. I siliconed the gap pretty well and, thinking about what the guy at the store said about the heat, left a small area open just in case. Put the storm collar back on and siliconed it really well. The next day involved a lot of wire brushing and painting the stove, which turned out beautiful. Last night we had a heavy heavy rain and I thought it'd be a good test. The top of the pipe is closed off for the summer so any leak would be coming from elsewhere. It all looked good at first and this morning there was a small 1 inch puddle on the stove, under the side where I'd left the small gap on the cone. My question... does that box absolutely need to be vented a little or can I gob up the cone entirely, under the collar, and be done with it? I really appreciate any advice.

 

[DanCorcoran]

I don't know the answer, but just want to compliment you on a clear and well-written post. And welcome to the Forum.

 

[begreen]

I'm not sure if this is your issue, but on our old Metalbestos pipe, I would get the same during a heavy rain. I ended up doing what you did, plus I siliconed the seam of the bottom length of pipe. That seemed to stop the leak once and for all.

 

[blades]

Your problem is up on the roof side, need to seal top of cone and then the storm collar , Got the same thing until I did that. Did not have anything to do with the ceiling support/transition box. Another thing that can cause this during a real windy storm is flue cap if you have the style that is just a top with screen all around. The one I have has deflectors for driven rain but no chance of ever plugging up from less than perfect burning.

 

[webbie]

The premise of the concern is probably true - that is, one of the functions of the flashing is to let air rise along the outside of the piping and therefore cool itself.

However, in the "real world" this probably is not needed for the pipe to be safe, because the same pipe is often allowed to be boxed in fairly tightly inside a living space. Still, I would suppose if we tested the pipe at the highest possible temperatures, such as in a lab, this cooling might be needed to achieve the specs.

In the real world, though, the pipe still cools itself greatly - that is, the same heat rises up into the flashing which is very cold and dissipates through the flashing. Also, in VT we can suppose the that attic and roof are all quite cool in the winter and thereby help cool the entire system.

In short, if I were using an insulated chimney to the very peak of it's abilities - for instance, running a multi-fuel boilers which can burn both fuels (total 300,000+ BTU) into it - and I were running this system year-round (in warmer weather), I would have some concern about closing off any spaces such as this. However, it would seem in a situation such as yours, the safety margin is quite high.

If you need a truly professional opinion on this, some of the insulated chimney companies actually do take support questions by email or fax and will answer them in a semi-official way (usually by their engineering staff).

As with many things, common sense often ties into the situation. A car might be rated to go from 0-60 in 6 seconds, but on an icy road that rating is subject to change (same with the braking ability!).

 

[webbie]

I might add that the space there is as much for the expansion of the piping - usually up and down - as it is for the air cooling. A long length of chimney could move up and down enough to easily break a seal.

 

[Highbeam]

I bet that your roofing is not done properly around the cone. Seldom is this done right and it can easily cause leaks. Can you look at the underside of the flashing area during a rain storm? To see where the water is coming from?

I had a similar drip onto my stove from the square ceiling box and upon inspection from the attic side of the roof I could see that the water was actually coming under the shingles and into the hole cutout for the stovepipe. I had a good roofer remedy the slight problem which caused this. My roof flashing is not gooped to the stove pipe. Further, there are little vent holes cut into the roof flashing near the top to prevent sealing the connection.

Roof leaks are bad news. The only place that silicone belongs is the storm collar. Even the nails for the roof flashing should be placed under shingles to prevent needing silicone on the nail heads.

 

[Fsappo]

I might add that the space there is as much for the expansion of the piping - usually up and down - as it is for the air cooling. A long length of chimney could move up and down enough to easily break a seal.

Or pull a flashing up. Some flashing manufacturers have the top edge of the flashing cone slotted just for the air flow. Could also just be a thing 1" thick or so storm collar. We use Metalbestos storm collars. They are huge and keep the rain out.

 

[jimbom]

I might add that the space there is as much for the expansion of the piping - usually up and down - as it is for the air cooling. A long length of chimney could move up and down enough to easily break a seal.

A 10 foot stainless chimney might lengthen 0.4 inches on a 300 °F temperature rise. Not sure of the specifics in your case, but thermal movement is an issue.

 

[cmonSTART]

The premise of the concern is probably true - that is, one of the functions of the flashing is to let air rise along the outside of the piping and therefore cool itself.

However, in the "real world" this probably is not needed for the pipe to be safe, because the same pipe is often allowed to be boxed in fairly tightly inside a living space. Still, I would suppose if we tested the pipe at the highest possible temperatures, such as in a lab, this cooling might be needed to achieve the specs.

In the real world, though, the pipe still cools itself greatly - that is, the same heat rises up into the flashing which is very cold and dissipates through the flashing. Also, in VT we can suppose the that attic and roof are all quite cool in the winter and thereby help cool the entire system.

In short, if I were using an insulated chimney to the very peak of it's abilities - for instance, running a multi-fuel boilers which can burn both fuels (total 300,000+ BTU) into it - and I were running this system year-round (in warmer weather), I would have some concern about closing off any spaces such as this. However, it would seem in a situation such as yours, the safety margin is quite high.

If you need a truly professional opinion on this, some of the insulated chimney companies actually do take support questions by email or fax and will answer them in a semi-official way (usually by their engineering staff).

As with many things, common sense often ties into the situation. A car might be rated to go from 0-60 in 6 seconds, but on an icy road that rating is subject to change (same with the braking ability!).

While I understand what Craig is saying here, just keep in mind that by modifying the chimney (or plugging the gap at the top of the flashing rather) you may assume some liability should you ever have some sort of house fire related to the chimney or stove. You will no longer have the pipe's UL listing on your side. (This is a big IF, mind you.)

Now the storm collar on the other hand, do make sure that thing is sealed really well with silicone. Also make sure the flashing is well sealed around the roof. Usually these two things are what lead to leaks.

 

[Pagey]

I too had a leak from the ceiling support box right after my install. Turns out water was leaking down the uncaulked vertical seam on the last length of Class A. The water would run down the seam all the way to the support box where it would collect in one corner (the box is apparently off level just enough for the water to favor that corner) and eventually drop onto the right, top plate on the stove.

As soon as the weather broke, the installer came back and ran a bead of silicone all the way up the last vertical seam. That stopped my "leaking support box". Give it a shot if you haven't.

 

[begreen]

That was my situation as well. Took me two years to figure it out.

 

[greythorn3]

hmmmm. maybe i should run silicon down the chimney seam before i got this problem also.

 

[Wade A.]

I'd also want to know if the overlapped seam/fold over tab on the storm collar is siliconed. Water running down the chimney pipe and finding a way under the collar and down the inside of the cone is a possibility.

 

[Wood Heat Stoves]

Unless the flashing has spacers formed in it like Dura Chimney has, you should seal around the pipe coming through the flashing, then pull the storm collar down over it, squishing the sealer under it, Then seal around the gap on top of the storm collar where it meets the chimney pipe. Also seal the seam on the flashing cone and the seam where the storm collar overlaps. If your getting water in the support box, it's running down the outside of the chimney. Wind can blow rain up and under the storm collar and if there's a gap it will run down the outside of the chimney and into the support box.

 

[tfdchief]

I installed my chimney, flashing and collar myself and not to sound arrogant, but I know what I am doing. I kept getting just a couple of drops of water on the outside of the SS Class A in the attic. I knew the flashing and sealing was not an issue but checked it all none the less. I had a temporary cap on top since the dealer did not have one the right brand. When the correct one came in, I put it on and sealed the seam in the exterior Class A. LEAK STOPPED. So, I am not sure which fixed the leak. It was very small and never made it inside the house that I could see.

Roof flashing of any kind, must be done correctly. Sometimes "HOW" may depend somewhat on the manufacture of the product. Read the instructions. Cheap products don't help either. I once threw away a roof vent (that I had to install fairly low on a roof) because the vent flange onto the roof was so small in relationship to the vent size itself, it simply leaked no matter how you installed it. Replaced it with a better product and it never leaked again.

There are many variables and small leaks are difficult to find. Lots of good advise here on the forum already. Pay attention to detail and you will figure it out. If all else fails, call the best roofing contractor you know. Chimney installers are not necessarily roofing experts.

Good Luck,
Steve

 

[BackwoodsVT]

You know, sometimes I wonder if the general public buying wood stoves, etc. realize what a wealth of info can be found on this forum. You've helped us along just about every step of the way and now I think we've got a really good idea as to what to do about out leaky chimney and support box. Thanks very much to all who took the time to offer such great advice. We really appreciate it. I'll be sure to check everything that was mentioned here and will keep in the mind the issue of expansion when the chimney system heats up. We have a relatively short chimney (one story home and just enough to clear the roof and also get a good draft) but I'll keep an eye on how the expansion affects the seals. I spoke with some guys at a stove shop and they said the Excel system they carry doesn't require ventilation for the flashing or support box. Just to be sure, I also took the advice offered here and contacted Excel's technical support. They replied very quickly and let me know that they generally don't recommend sealing the flashing to the chimney but that's because of the expansion factor. They said that 10 or more feet between the support box and the flashing could expand just enough to pull the silicone seal loose if there was a chimney fire. That's some major heat there and having some water leak in the house might not be my biggest concern at the time. But regular expansion and contraction is something to keep in mind, no matter the chimney size. The tech support guy did go on to say that they do know of many installations where the chimney is sealed to the cone without any problems and finished by saying their flashing requires no ventilation.

So I'll go do another inspection and check the things mentioned in your replies. If I do end up sealing it completely, I'll be checking the seal to see how it holds up over time.

Thanks again everyone.

 

[begreen]

Try sealing the vertical seam on the length of pipe that goes through the storm collar too. There's nothing to lose by sealing it and for some of us it was the key to a dry system.

 

[BackwoodsVT]

Absolutely. I forgot to mention that's something that will definitely get done while I'm up there.

 

[begreen]

Good luck and keep us posted on how it works out for you.

 

[tfdchief]

Just a note, I used silver silicone for the vertical seam seal and you can't even see it from the ground.

 

[oldspark]

Just a note, I used silver silicone for the vertical seam seal and you can't even see it from the ground.

Vertical seam on the chimney pipe? Not sure I understand what seam you guys are talking about.

 

[tfdchief]

Just a note, I used silver silicone for the vertical seam seal and you can't even see it from the ground.

Vertical seam on the chimney pipe? Not sure I understand what seam you guys are talking about.

Yes, the vertical seam in the S/S Class A Chimney Pipe that is above the roof and flashing/storm collar. Or anyway that's what I was talking about.

 

[oldspark]

Just a note, I used silver silicone for the vertical seam seal and you can't even see it from the ground.

Vertical seam on the chimney pipe? Not sure I understand what seam you guys are talking about.

Yes, the vertical seam in the S/S Class A Chimney Pipe that is above the roof and flashing/storm collar. Or anyway that's what I was talking about.

Not all brands have this correct? I see no vertical seem on my dura tech (or I am an idiot).

 

[tfdchief]

Not all brands have this correct? I see no vertical seem on my dura tech (or I am an idiot).

BG, someone, help. I don't know anything about that brand of pipe, but I don't know how they could make it any other way.