I cleaned my flue this weekend after 2 solid months of burning. I have a 25' single wall, flexible, 6" SS flue liner in an exterior chimney. I burned a lot of pine in the shoulder season and mostly cherry and oak now that it has gotten cold. I have a moisture meter and all of the wood is 16-17% MC. The flue liner had an even coating of flat black powder on it - up to maybe 1/8" thick. It was not shiny and was not stuck on it at all. It all came off very easily. I was surprised at how much there was after only 2 months of burning (maybe 1.5 cords of wood). I cleaned top down and the picture is was what was in the fire box when I got done. Is normal ash grey? Is this creosote because it is black? If so, why am I getting this build up? I'm guessing it is because I have an exterior chimney and the flue is too cold. I burn only dry wood (again, 16% MC, no hissing, no sputtering, no water coming out the ends). I do not get any black coatings inside the insert and I do not get any creosote on my glass after overnight burns etc. Could be that the pine makes more ash than hardwood. I plan on cleaning the flue again in another 2 months and I'll see if it is different after only burning hardwood. So, normal? Nothing to worry about? Concerns? Thanks.
nothing is really jumping out at me from the picture. looks like its predominatly inert ash. the fact it swept off so easily is always a good sign means there has been plenty of temperature up in the flue so its stayed dry all the way up. keeping the flue temps above 212F is one of the biggest keys to successful buring and a clean flue. this prevents moisture buildup in the flue and the eventual creation of creosote.
That's internal flue temps of 212, not surface magnet temperature, to prevent condensation. You're burning wood in a device that has a particulate emission rate. That's soot. Soot is what you have there. I have a feeling that the corrugated interior of a liner has more surface area per foot to accumulate this stuff.
I wouldn't be concerned with that from a safety standpoint. Looks to be mostly ash and soot, and the little grooves in the corrugated liner are apt to collect that...especially 25 ft of it.
Thanks guys, I appreciate the feedback. Its what I was thinking --- 25' of little ridges is a lot of space for soot to latch on to. I've burned 2 cords of wood and only taken about 2 gallons of ash out of the firebox....so the rest of it is going somewhere (up the flue). Its weird that the ash I take out of the insert is grey and the soot in the flue is black. But then I guess that is the difference in weight / size between what goes up vs. what is left behind.
this would be correct. the ash that stays in the firebox is subjected to more heat for more time so it gets literally burned white. when ash is completely white there is nothni left in it , its completely inert.
FreeBTU's, is this an uninsulated flue liner in a stone chimney? If it is that could be part of the problem, a little harder to keep the flue temp up.
Yes, the liner in not insulated. It is a brick chimney with a clay flue. The chimney is exterior (on the end of the house). The company that installed my insert and liner put in the uninsulated liner, no heat plate, and did not even attach the plate on the top of the chimney (the first winter it blew off to one side and left a 3" wide air gap right to the flue. Wish I knew back during the install what I know now after reading these forums. I have since stuffed roxul into the flue above my insert and added a heat plate there. I also stuffed some roxul down the flue from the top of the chimney around the liner and screwed the top plate to the bricks using tapcons. I don't get drafts coming out around my insert anymore and it is way easier to heat up my flue. I did all that work myself before this season. It looks like things are working well now, but the installer charged me an arm and a leg and they should have done it right. Turns out my neighbor used the same installer for their woodstove and they really screwed the pooch on that job and they have water coming into their living room and their wall has some rot now. Last I heard they are going after the company in court. The funny thing about it was that the company required me to get a building permit ($). The building inspector came after the install and didn't even measure clearances or look at anything. He just asked me if that company (by name) installed it. I said yes and he said ok, its approved and if I had put it in myself it would not have been approved. If I had done it myself I would researched it and done it right.
That sucks, in many cases you are better off doing the research and doing it your self, not always easy to find a reputable business.
"The thermal characteristics of masonry chimneys probably fall somewhere in between insulated factory-built chimneys and uninsulated stovepipe. Most masonry chimneys are not well-insulated, and those located on the exterior of a heated structure will present a relatively cool environment. Their high mass and thermal inertia will inhibit rapid temperature rise from a brief application of heat. "
