Oh man...that black below the clean out and the efflorescence on the brick spells lots of condensation to me. At some point you should clean and water proof that entire chimney tip top to bottom with a high quality chimney water proofing like that of How to Waterproof Your Chimney and Prevent Chimney Leaks - SaverSystems You can do it yourself, but you might be better off letting a pro do it. They will have the cleaning products and the water-proofing products of similar and sometimes they have pro products (non-consumer type) as well versus consumer versions, which both can work well. I am thinking that chimney could be leaking somewhere. I don’t think that is just from running your stove, but it could be. You certainly can’t lose by having a thorough inspection done by your trustworthy local sweep. The top may be leaking somehow.
So is it safe to use? Should I stop burning it? I feel like this has been going on for a while now. This is why I’ve been concerned with the condensation. My chimney sweep didn’t say anything about the condensation below the clean out. He did go out there to clean out what fell to the bottom when he cleaned it.
I can’t answer that. I would not feel comfortable answering that question...one better decided between you and a good chimney sweep. I had some concerns about my chimney and wanted to hear my options, so I had a chimney sweep come for an inspection. That puts the liability on them. Once things meet inspection you can easily maintain or allow them to keep assuming the liability maintaining it for you. Peace of mind is hard to put a price on. An insulated liner and a leak free chimney is your best bang for your buck and will help you meet current fire codes. Heatshield coating inside a clay liner, or similar, meets current clearance to combustible codes. It is not cheap. Lots of products out there. Just know that some are re-branded, but still made by Saver Systems in Richmond, Indiana. However, there are other manufacturers of other quality products as well. You can also have the clay ripped out, re-line with an insulated stainless steel liner, OR have this done... Cast in Place Chimney Liner
Id drop an insulated liner down it and call it a day. The masonry, especially on the exterior, is going to absorb all the heat from your flue gasses. Thats why you've got creosote running out the top and bottom of the chimney. 20' liner, insulation, a T with a removable snout to make the liner installation easy and a new cap. I would also pack the top of the chimney with Rock Wool prior to securing the cap. Itll help keep drafts down. ETA: if you have 13x13 clay tiles in there now, no need to remove them. If you have 9x13, you'll have to ovalize the liner to get it down. Save your money on the inspection and put it towards the liner.
I was running into similar issues before I lined my chimney. I have a 9x12 clay flue, which was clearly oversized for my keystone. On start up, I would get bad condensation that looks like yours. My clean out would be a couple inches deep of liquid creosote and similar efflorescence. Absolutely terrible experience cleaning that daily. Of course the speculation was "wet wood" however I'm typically 3-4 years ahead, and it all lives under cover and 15-20% consistently. I don't know what your wood supply looks like, but to me that's step 1. Make sure you have a good seasoned wood supply Step 2 would be a liner. I no longer have any condensation issues, so life is good. Not the same stove, but I typically don't engage the cat until I'm @ 350-400 on the flue probe regardless of cold or hot start. From there, I leave the air a bit more open than my final setting for 15-30 min. At that point I can normally drop to cruise setting, and not touch it again for 10-12 hours depending on size of the load and species.
My clay liner is 8 inch round. Can a 6 inch insulated liner be stuffed down that? What I really want to do is go with double wall pipe to a ceiling support box then thru the roof with stainless steel insulated pipe, but I highly doubt my wife is going to let me do that.
Uninsulated it would...and if your mortar joints are really clean, and there's no offsets or other problems, it MIGHT fit with insulation (approx 7.5" OD with insulation) You might consider a preinsulated liner too...they are a touch smaller OD, and tougher, if it's a tight fit...
So a preinsulated liner would be something like this? It says to add 1.5 inches for full diameter so I’m interpreting that as it would be 7.5 inches total and would fit down my existing clay flue. Would that be insulated enough to provide me some protection from it being an outdoor chimney, solve my condensation problems, and improve my stove performance?
You'd need to drop a pipe, or small bucket, something that is 7.5" OD down the chimney to check, but if it fits, yes it should improve your problems greatly.
I used a 5.5” insulated liner in mine as I had same size flue. That’s a option I guess, My stove runs well with it.
