Yet another plugged chimney cap question.

[BruceB]

Hi all,

I'm new to the forum, but not new to wood stoves as I grew up with one in the house as a kid and have had one in most of the houses I've lived in for the last 60 years. I'm not a wood stove expert, but do have a fair amount of experience, but today I ran into an issue that has me scratching my head.

The damn chimney cap plugged up.

I've had this stove (and cap) for about 13 years, clean the chimney myself every fall and have never even had to think about cleaning the grating on the cap because it's never dirty. Today, about 3 months into the heating season, I noticed smoke coming out of the chimney.....on the inside of the house. Seemed odd, but I checked my coffee, and there wasn't anything in it that would make me see things, so I damped the stove down and went up on the roof after it had time to cool down. The cap, which is one that is a matrix of approximately 1/2" holes, was completely plugged up. It's never been dirty enough to do more than smack it with my hand for 13 seasons, and now it's plugged after 3 months of burning? What the....heck? I ran a brush through the chimney and only got about 2 double handfuls of ash out, so it doesn't seem the chimney was sooted up real bad. Now I'm wondering what I'm missing in this little mystery.

I buy my wood a logging truck at a time, and cut my firewood at least a year in advance. The truck-load stack is kept tarped and this year's firewood was the tail end of a 5 year old pile. The cut/split wood is under a shed roof on the south side of my shop building for at least a year, so I have no doubt that the wood I'm burning is dry. Also, I've been burning from the same truck-load for the previous 4 years, so it doesn't seem likely that I'm dealing with green wood all of a sudden. We use the stove every day; let the first fire run hot until the the chimney temp is showing about 600 degrees, then damp it down, usually until we light a second fire in the evening. I don't bank the stove at night unless it's a cold one, and we don't get that very often here in Spokane, so I don't see much creosote build up from smoldering fires. But now my cap plugged up and I don't know why. I don't want to just change out to an un-screened cap because I feel that's just covering up a symptom. I'd really like to know what I'm doing wrong before the house burns down; I don't have enough energy to build another one.

Any ideas sure would be welcome.

Thanks!
Bruce

 

[moresnow]

Welcome to Hearth. What stove are you using?

 

[BruceB]

It's a Pacific Energy series D Fusion, which looks to be about the same as the Super LE in their current line up. About a 2 cubic foot firebox, no catalyst and it is pulling combustion air from within the house. The chimney is about 15' of single wall and another 5 or 6 feet of whatever insulated pipe was in use 13 years ago. The top of the chimney is about 3 feet above the ridge.

My biggest concern with this is that something has changed, but I don't know what. The stove seems to be burning the same as it always has, but is it possible that that I've got a problem with the stove that isn't obvious?

 

[begreen]

The only time I have had a cap plug is with wet wood. In our case it was 3 yr old maple. Although it should have been dry, parts of the stack were not due to the tarp sagging and having a leak. The best way to figure out what is happening is to assume nothing. A log that was sitting on the ground, even for 4 yrs, can still be damp. Resplit some of the thickest, heaviest splits and test for moisture on the freshly exposed face of the wood.

If some of the wood is showing about 23% then that is likely the issue. The 15' of single-wall stove pipe is also exacerbating the situation by cooling down the flue gases too much. Single-wall stove pipe is for short runs. Stoves that run with a cooler flue temp are recommended to use double-wall stove pipe exclusively.

 

[Highbeam]

My bird screen kept clogging too despite dry wood and a clean chimney. The screen on my duravent brand system is optional and removable so off it went. No screen, no problem. I don’t really need to know why it clogged but I know it wasn’t wood quality or burning practice.

I am jealous of your ability to receive a full logging truck of logs. Due to my property configuration I’m almost stuck with dump truck loads of 14’ lengths.

 

[BruceB]

Highbeam,
Although I really like going out and cutting firewood, it really is nice to be able to get wood by the truck-load, although they're really not much longer than the 14's you're getting. The best part is that I built forks for my tractor so I can load several logs at a time AND raise them to waist height for cutting. Depending on the log size, I can cut 5 or 6 to length at a time and don't have to bend over.

Begreen,
The logs are piled on a couple of cross logs when they come off of the logging truck, so don't actually rest on the ground. The tarp does pool and leak some water, but the wood also spends a minimum of a year under a shed roof after I cut and split it, so I'd wager it's dry. That being said, I never pass up an opportunity to buy another tool so I'll be ordering a moisture meter today. Thanks for the excuse!

Installing double wall pipe makes perfect sense, although I don't know why it would work ok for 13 years, then suddenly not work ok. I'll look into upgrading it, though.

Thanks for the responses!

 

[begreen]

The flue system may be just marginally keeping the flue gases hot enough to stay below the condensation point for creosote. And possibly some of the wood might be just a little bit wetter. If that is the case then a small change could tip the balance.

 

[BruceB]

You're probably right. Moisture meter should be here by Tuesday; I'll let you know what I find out.

 

[blades]

screens plug- for all kinds of reasons- no screen no plug. if by local rules you have to have a screen go with at least 1" sq. those 1/2" buggers do just that, get buggered up quick. dosen't take much to plug the1/2 screen a little too much moisture being burned off on start up and it's off to the races.

 

[xman23]

Wetter wood, burning colder is about the only change you could have made. If you haven't ever cleaned the screen, is it possible it's been slowly closing up? The cap is not insulated, like the chimney, so it creosotes quickly. I would just be concerned with whats in the chimney. The cap is a good indicator of an issue, but other than plugging it doesn't matter much.

I think mine was a 1/4 screen. It was the first year with fresh oak. I got the wood to burn, but 1 1/2 months later, the screen was plugged. Removed the screen. That was 20 years ago. I have gotten a few blue birds to come down the chimney. I guess now that I burn better wood, a screen would work, but I would do 1 inch.

 

[BruceB]

The moisture meter arrived today, so I've out playing in the wood pile. I re-split some of this year's wood (cut and split last year), and the moisture ranged from 9% to 12%. I also checked several pieces from next year's wood that I cut and split a few months ago. The highest reading I got was 16%, but it obviously would have been quite a bit higher when first cut. I'm going to assume that I got some of that mixed in with my seasoned wood and it lowered temps enough to give me problems. As Begreen pointed out in his post, I screwed up when I installed a lengthy section of single wall pipe and I expect that is what the real problem is. Apparently, I've gotten lucky for the last 13 years and never had a problem with a marginal installation, but now it's on my short list to replace that pipe with double wall. I realize I could just put a new cap on that doesn't have a screen, but I think the plugged cap was a symptom of the problem and I'd rather fix the actual problem.

Thanks everybody for all the suggestions and help!

 

[Highbeam]

The moisture meter arrived today, so I've out playing in the wood pile. I re-split some of this year's wood (cut and split last year), and the moisture ranged from 9% to 12%. I also checked several pieces from next year's wood that I cut and split a few months ago. The highest reading I got was 16%, but it obviously would have been quite a bit higher when first cut. I'm going to assume that I got some of that mixed in with my seasoned wood and it lowered temps enough to give me problems. As Begreen pointed out in his post, I screwed up when I installed a lengthy section of single wall pipe and I expect that is what the real problem is. Apparently, I've gotten lucky for the last 13 years and never had a problem with a marginal installation, but now it's on my short list to replace that pipe with double wall. I realize I could just put a new cap on that doesn't have a screen, but I think the plugged cap was a symptom of the problem and I'd rather fix the actual problem.

Thanks everybody for all the suggestions and help!

One last thing, moisture meters are calibrated to work on 70 degree wood so you're supposed to bring it inside for a day to warm up before splitting and reading the fresh face. Colder wood reads drier than it really is.

 

[rwhite]

Wetter wood, burning colder is about the only change you could have made. If you haven't ever cleaned the screen, is it possible it's been slowly closing up? The cap is not insulated, like the chimney, so it creosotes quickly. I would just be concerned with whats in the chimney. The cap is a good indicator of an issue, but other than plugging it doesn't matter much.

I think mine was a 1/4 screen. It was the first year with fresh oak. I got the wood to burn, but 1 1/2 months later, the screen was plugged. Removed the screen. That was 20 years ago. I have gotten a few blue birds to come down the chimney. I guess now that I burn better wood, a screen would work, but I would do 1 inch.

I've had blue birds in my stove twice. Being the softy I am, plus I love blue birds, I let them out. An ash covered bird hitting the ceiling 100 times on the way out the door makes quite a mess

 

[Rickb]

The moisture meter arrived today, so I've out playing in the wood pile. I re-split some of this year's wood (cut and split last year), and the moisture ranged from 9% to 12%.

That is lower then my wood after it seasons for 3 years. Unless your in a desert I cant see this being correct.

Mine will get down to 13-15% but not lower. If can sit for 5 years and still be 14%. Fresh split ash that was split 3 years ago that im burning right now is 15%. Was at 20% after a year, just doesnt really drop fast once you get below 15% do to out ambient humidity.

 

[Highbeam]

That is lower then my wood after it seasons for 3 years. Unless your in a desert I cant see this being correct.

Mine will get down to 13-15% but not lower. If can sit for 5 years and still be 14%. Fresh split ash that was split 3 years ago that im burning right now is 15%. Was at 20% after a year, just doesnt really drop fast once you get below 15% do to out ambient humidity.

That final equilibrium moisture content is highly location dependent. In my wet area I’m about like you with 14% equilibrium. The OP is pretty much in a desert so he might get a little lower.

 

[MTASH]

Correct, many areas in the northern Rockies are arid. My area in particular only gets around 13" of precipitation annually, and it's not uncommon to have low humidity in the teens or single digits. My MC readings are similar to the OP.