Why is my chimney cap plugging up????

[longboarder2]

over the last few years since my untimely chimney fire (feb. 2012), we've had great success burning our Harman sf160 smoke dragon. Three weeks ago, I had the chimney swept and oddly the sweep got nearly nothing out of the pipe (usually yields a large coffee can of gray ash and dry black soot). About four days after his visit, I noticed the unit would puff in when I opened it and the flame was very dark orange and "lazy". Checked the draft----only at .04. I called him back: he returned to find my topper and the top few inches of the pipe plugged nearly solid with dry black soot (usually sweeps from the basement clean out up and then pulls everything down) He cleaned everything again and got the usual findings (figured it hung up for some reason from the last visit so he swept down from the roof this time). Draft was .08-.10 with wind gusts taking slightly higher occasionally. That was a week ago yesterday. Today---stove was lazy starting with the draft door open and the cap looks black as ever up there. Draft was at .05-.06.

I'm burning the same way with the same amount of air intake as I have for the last three seasons. The unit NEVER IDLES---air intake is always propped open about 3/8" on the bottom. It burns out at night and I relight in the morning. Have about 30% of the shaker grate covered with steel plates to preserve coals for the mornings and maintains a nice glowing orange bed of coals during regular burning. Never burn more than five splits at a time---usually 2 to 3. Lots of fine light gray ash on the loading door and inside the fire box---I've never had the 1/4" buildup of creosote harman says is normal on the inside of the fire box. Stack temp (measured 18" off the collar) usually hovers around 250-300, 350 after putting in a couple fresh splits and calms down to around 200-250 as the wood burns down prior to loading. Usually do a 500 degree hot burn once per week.

Approx. 25' of 7" stainless insulated double wall flue pipe, topper is 18" off the top of the chase, and the topper is expanded metal stainless mesh approx 8" tall---no wind shielding.

I'm burning two-year old seasoned wood (always top-covered) 80% oak and other species like locust, small amount of maple, a dash of holly. The only difference this year compared to previous years, I'm burning some sweet gum I got from a roadside scrounge--- I'd say lately each heaping wheelbarrow has about three or four gum splits in it on average, but that's not consistent.

Any thoughts on why I'm getting plugged up with black soot in a weeks time?

 

[Fsappo]

Not sure how that small amount of gum would impact things. Only cooled particulates attach themselves to chimney screens. I get a lot of calls when its really cold, as it creates lower gas temps at chimney tops, that and ice from the moisture going up the chimney forming. Things around houses can slowly change draft and wind patters, new construction, trees growing, etc. Also, if something changed the makeup air in the home, such as a new appliance which uses room air for combustions, additional air sealing, etc.

Just some random thoughts.

 

[longboarder2]

Update: scaled the snowy roof with a scrub brush, scrubbed out the expanded metal and viola!, drafting .10 again steady. Discovered that when the sweep was here, one of us closed the idle draft holes on the draft door. Not sure if this could be the culprit, but that is the only change that has been made in the last three burning seasons. Hard to imagine that two 3/4" holes in the draft door could make that much of a difference, but I'm out of ideas.

 

[NCFord]

I am not sure if you are talking about the spark arrester or just the cap buy mine does the same thing. I just removed the spark arrester and problem solved.

 

[Grigg]

Same here, was plugging up over just a week or two. Removed screen and put the cap back on, no trouble in several years now. Originally it happened with one of those double 55 gallon drum stoves, which I think cooled things off to much and the soot and creosote condensed on the screen. Removing the screen solved that and we've used 2 different better wood stoves now and still no trouble, and still no screen. Also after getting rid of the 55 gallon drum thing I brush the flue much less often, once a year just to be sure. Previously I would brush it several times a season when it'd be restricted enough smoke wanted to escape inside.

 

[BoilerMan]

I too would not have a screen in a wood fired chimney during the regular burning season. A cap is an absolute must though. I have a piece of plywood I put in the cover of mine in the off season after my annual spring brushing. I put a sticky note on the boiler to go up and remove the plywood before lighting the first fire in the fall . Keeps the moisture out and the birds from making and kind of lodging/filling of the flue.

TS

 

[NCFord]

Good idea on the plywood in the off season. I cleaned out the chimney in aug. or sept. and found a couple of dead bats and a bird. I think I will put the screen or plywood in for the summer this year.

 

[Motor7]

x4 on ditching the screen. Some caps like my Windbeater was designed without a screen at all.

LongBoarder, you're "settled down" burn should be higher than 250, as anything lower than that(except at the end of a burn during the coaling stage) will make creosote. I think you need to fed it a little more air......

 

[maple1]

x4 on ditching the screen. Some caps like my Windbeater was designed without a screen at all.

LongBoarder, you're "settled down" burn should be higher than 250, as anything lower than that(except at the end of a burn during the coaling stage) will make creosote. I think you need to fed it a little more air......

My chimney cap also came with no screen. They can be a creosote catcher. Depending how coarse the screen is - maybe cut it down some so it isn't as fine?

On the temps - that can depend on how they are being measured. I have a magnetic one right beside a probe. The probe reads 100c hotter than the magnetic when burning. That's at temps that max at 250c on the probe. If I was going by the magnetic one, I would be wondering if the fire even got burning or not.

 

[Motor7]

maple you are right, that's why I have a digital w/probe....my magnetic one is way off.