Was it really windy too? From your attic you should be able to see the gap that is open to the stars between the storm collar and the roof jack. Lots of wind could blow water under the collar if it placed really high.
I had water blow up under my storm collar and drip down through the flashing vents and onto my stove during a super-windy heavy rain event. That happend only once. We had more really heavy rain last night, but no drippy. I would guess that it is an isolated event.
I don't know if this is your problem, but I had water dripping out around my stove pipe adapter immediately after I put in my chimney this year. I was confused, because I was meticulous about sealing the flashing and storm collar. I even went in the attic during a rain and verified it was not coming in that way. It turned out the water was wicking in at the seams of the chimney sections and getting in the insulation of the chinmey and dripping down that way. I caulked down the seams and at each joint on the chimney outside and have not have a problem since. Others her have had the same problem, and that's actually how I learned about it. I have the Supervent brand of chimney. I think others with the problem had the same brand too.
It has happened a couple of times before. Yes, it is a Supervent chimney. No attic, cathedral ceiling. Plan on going on roof tomorrow to see if we see anything. What kind of caulk or sealant should we use if we determine it is from the chimney itself?
If it was SuperVent, I can help with some info.... John V. (VP Marketing/Selkirk).
If the Chimney is not enclosed below the roof line, you can use duct tape to seal the vents in the Roof Flashing. The ventilation is only required where the system is boxed in through the attic space.
On sealant, you can only use high temp (red) silicone or black milpak.
All I had at the time was some GE 100% silicone formulated for metal. I did not use any "High Temp" silicone because I could not find any for sale down here. I have not run my stove yet, but I am hoping it will not get so hot on the outside chinmey that it matters. I finally saw some Rutlant high temp silicone not long ago at a Tractor Supply store here. If I would have known they had it, I would have used that. If it burns off, I will buy a tube of that and re-do it. You may want to use the high temp stuff from the start if you can find it. It is my understanding that it has to be at least 400 degrees F for the regular stuff to burn off, so I am hoping I am fine.
And, by the way, there is not much to see on the outside if it is wicking in. I used silicone on the seams just hoping that was the cause, and it worked.
My goofy installers used regular white house caulk at the storm collar to chimney ring joint. They even put it on crooked. One of the biggest gripes I have about the install is that part of their job. It hasn't burned off though.
Talked to someone at Selkirk. They thought it probably was from the venting slots in the flashing since it only happens with horizontal rain. They suggested to run a bead of silicone along bottom of slots, but not to cover up the slots? Haven't gone up on roof yet. Never noticed any slots when we cleaned chimney, but we weren't looking for them. I guess we will try this.
The slots are on the flashing, not the collar. If you look up under the collar, you'll see the slots, which is what caused my leak. As for caulking, I used the blue or black high-temp silicone from the auto parts store made for engine gakets (i.e. water pumps, valve cover gaskets). This stuff has held up for many years at my place, and it comes in a small tube, so not too much waste. I used it for caulking the storm collar/chimney connection.