Poor Draft

[flmaxey]

I've used a catalytic wood stove for well over 20 years, an Energy King Bay 2000c fireplace insert that can be converted to a free standing stove. (I've used it both ways.)

Regarding the draft problem:
In my new house, when I open the stove door, smoke almost always comes out into the room. I know there are a few factors contributing to the poor draft problem which I'll detail as follows.

- I have an Englander NC30 which is an awesome stove, but it's more stove than I need in our new place. (To some degree this was intentional. Given our location at 2000 ft, sub-zero tempuratures are a real possibility.) With the exception of truly cold days (like today) I can't burn it really hot. (Also, much as I've done with the Energy King, I like to load it up and shut down the draft so it will "simmer" all night.)

- I have an 8x12 clay flue lined chimney. I built it, with the help of my brother-in-law, who talked me into what I thought was an overly large liner. (I was thinking 6" would be enough for a wood stove, but it is what it is.)

- The chimney itself is not short but, the actual working distance between the thimble to the top is a bit over 7'. I'm in a Rancher with the thimble fairly close to the ceiling. (See the photo). The chimney height is easily 2' higher than anything within 10' and a bit above the peak of the roof.

- I have a fairly long horizontal pipe run. In the photo below, 3' 2" are visible and there's at least 12" more for the thimble.

I've learned a few work-arounds such as:

- Open the draft, wide open, 10 to 15 minutes before loading wood. (Clears the smoke, heats the chimney.)
- Allow wood to burn to coals before opening the door. (Little to no wood gas or smoke.)
- Be prepared, do it quickly.
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To improve the draft:
I was thinking about coming out of the stove and at 8 to 12", use a 45 degree for a diagonal run, and about 8 to 12" from the wall, using another 45 degree to go horizontal into the thimble. That should accelerate the smoke path and reduce the horizontal run to about 2'.



I'd rather not extend the chimney, if at all possible. (Having to climb up a ladder to clean it would not be ideal.) And again, for the sake of cleaning simplicity, I'd rather not line it with flexible stainless.
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I'd like to get forum users' opinions on the following, so called, "vacuum caps". There's a breeze here that's fairly constant so, if these things work, I'm willing to give a model that's known to work well a try.

https://www.amazon.com/gp/product/B009KUTR5K/?tag=hearthamazon-20

https://www.amazon.com/gp/product/B00O3IO2CC/?tag=hearthamazon-20

Any comments / thoughts will be appreciated.
Thanks

 

[begreen]

I was thinking about coming out of the stove and at 8 to 12", use a 45 degree for a diagonal run, and about 8 to 12" from the wall, using another 45 degree to go horizontal into the thimble. That should accelerate the smoke path and reduce the horizontal run to about 2'.

That will help, but venting into a 72 sq in area flue is the big problem as well as the short chimney. The chimney liner is about 2.5 times the area needed for the 30-NC. It is slowing down the draft. This trifecta of problems spells poor performance. It's not surprising there are issues with a short chimney combined with the horizontal run venting into a too large chimney.

Are you seeing any secondary combustion? To remedy it will need all 3 issues addressed. Use the 45s for an offset, install a stainless 6" liner and swap out the stove to one that can work on a shorter chimney. If you are looking at downsizing the stove the True North TN20 or PE Super 27 will work on a shorter flue.

 

[HomeinPA]

I've used a catalytic wood stove for well over 20 years, an Energy King Bay 2000c fireplace insert that can be converted to a free standing stove. (I've used it both ways.)

Regarding the draft problem:
In my new house, when I open the stove door, smoke almost always comes out into the room. I know there are a few factors contributing to the poor draft problem which I'll detail as follows.

- I have an Englander NC30 which is an awesome stove, but it's more stove than I need in our new place. (To some degree this was intentional. Given our location at 2000 ft, sub-zero tempuratures are a real possibility.) With the exception of truly cold days (like today) I can't burn it really hot. (Also, much as I've done with the Energy King, I like to load it up and shut down the draft so it will "simmer" all night.)

- I have an 8x12 clay flue lined chimney. I built it, with the help of my brother-in-law, who talked me into what I thought was an overly large liner. (I was thinking 6" would be enough for a wood stove, but it is what it is.)

- The chimney itself is not short but, the actual working distance between the thimble to the top is a bit over 7'. I'm in a Rancher with the thimble fairly close to the ceiling. (See the photo). The chimney height is easily 2' higher than anything within 10' and a bit above the peak of the roof.

- I have a fairly long horizontal pipe run. In the photo below, 3' 2" are visible and there's at least 12" more for the thimble.


___________________________________________________________

To improve the draft:
I was thinking about coming out of the stove and at 8 to 12", use a 45 degree for a diagonal run, and about 8 to 12" from the wall, using another 45 degree to go horizontal into the thimble. That should accelerate the smoke path and reduce the horizontal run to about 2'.


View attachment 238806
I'd rather not extend the chimney, if at all possible. (Having to climb up a ladder to clean it would not be ideal.) And again, for the sake of cleaning simplicity, I'd rather not line it with flexible stainless.
_______________________________________________________

Thanks

You basically have the same length vertical piping as horizontal. The "oversized" flue is really not the issue in my opinion as much as the chimney is way to short. Many stoves have written in the paperwork somewhere that a 15' flue is the minimum they suggest for venting a stove. What does yours say? You don't mention how high the chimney is to the dwelling. Are you familiar with the 2:3:10 rule? A house with a 4:12 roof must rise a minimum of 64" above where it passes through the high side of the roof when it is more than 10 feet from any part of the structure. Even though you don't want to, I think you need to raise the chimney.

 

[Eureka]

I’ll agree that your chimney is too short and WAY too big. You need a 6” chimney and probably twice as long to work well with that stove

 

[moresnow]

To remedy it will need all 3 issues addressed. Use the 45s for an offset, install a stainless 6" liner and swap out the stove to one that can work on a shorter chimney. If you are looking at downsizing the stove the True North TN20 or PE Super 27 will work on a shorter flue.

Do this.

Or keep your stove and install the 45's,also install the correct diameter stainlesss liner up to the top of the existing masonry chimney where you can transition to class A sections until you develop acceptable draw. Even the 6" liner to the top of your existing masonry might make a significant difference depending on how well your stove is getting make up air etc.

Tell your bro in law to get a username/password here. Sounds like he could use some guidance!

 

[kennyp2339]

To truly rectify the problem I'd install a 6" liner to a anchor plate on top of the chimney and add 3ft of class 1 chimney pipe. Can you explain why you believe adding a stainless steel liner will make cleaning more difficult? I would think it would make cleaning way easier 6" round poly brush or soot eater.

 

[flmaxey]

I would have been back with some answers to questions sooner, but life is what it is.

First I'd like to thank all for their responses. I sincerely appreciate your time, effort and experience.

To answer a few questions or notes first:

- When the stove gets up to temp, the secondary reburn, in the NC30 is taking place. This was the first thing I checked. The holes in the stainless pipes appear as it they have a propane flame coming from them (remarkable).
- I have to give my brother-in-law a pass on this one. He normally installs a chimney on the end of house and sets it 36" or a bit more about the peak. This is almost always in excess of 15', even on a single floor home. And when I talked to him about it, the first thing he said was adding just a few more feet could make a heck of a difference.
- When he suggested the tile size when we built it; I checked the stove doc's and, apparently, the OEM states that 8x12 is the max, but OK. (They probably didn't take into account what the effective minimum vertical height would be.)
- The actual chimney height is about 15' or so, from the ground. (But the house is built over a block crawl space so that effectively subtracts out 2', 6".)
- The chimney is built in the middle of the long side of a rancher, against the lower edge of the roof.
- The finished height is 48" above the lower edge of roof, it's better than 24" above anything within10' and, since the pitch is shallow, the finished top of the chimney is above the roof peak.

- Regarding a stainless liner. Given the wall thickness of a typical kit, I was somewhat skeptical about how many cleaning cycles they could endure with a wire brush. It takes a bit of force and work with a wire brush to remove hardened creosote. However, I have yet to find any horror stories on-line about torn or punctured liners so I'm guessing they're not as fragile as I thought they might be.
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In any case,
I found the core issue behind the smoke. The horizontal pipe in the pic above was almost completely clogged, after a mere 4 months of continuous use. I believe this is due to the stove's sizeable output, which I chocked down to keep interior temps in the mid to lower 70's. Second, for a fluid dynamic's prospective, hot smoke moves like an upside-down water fall. It travels fast up the vertical pipe piece, then slows down (back pressure) and cools while running through the long'ish horizontal pipe. Combining that with running the stove on the cold side and the result was creosote city for the metal pipes. (Curiously, the masonry chimney section is OK.)

I cleaned the pipes, refitted the pipe with 2 each 45 degree elbows and created an almost direct 45 degree run from the stove to the thimble. (The max horizontal run now, is through the thimble itself - a bit over 12".) Then, I installed this (broken link removed to https://www.famcomfg.com/product/square-flue-vacuum-cap-galvanized/).
While I expected some drawn with the pipes clean and a more vertical pipe run, with the vacu-cap, the difference was remarkable. Even without a fire, I could feel air passing by my hand. Since we have a near constant 3 - 5 mph breeze (and up), the cap works well in this location.

Now, I can built a fire easily in 10 minutes and be making real heat in 20 minutes or so. Now, I have to mind the draft. I can't run it wide open, or the stove will over-fire. (This is a nice problem to have, versus fighting to keep a fire alive.) On really windy days I have to be just a bit more conservative on the draft than usual because of the effect of the cap. (Another bonus of this cap because without it, depending on conditions, a windy day can be dampen down a fire somewhat.)

The lesson learned here is, I have to run this stove in it's operating range, particularly when fresh wood has been added (where wood gas is plentiful). This was great, particularly during this last arctic blast. (With the temp in the low teens outside, it was in the mid to upper 70's inside.) At other times it's upper 70's to lower 80's. My wife is loving it, but I have to wear shorts and tee shirts. :- )
(OR)
If I choke the stove down and run it on the cold side, that may mean cleaning the metal pipes every 2 months.

The only Con I can come up with, for the vacu-cap, is the drippings. Since it's metal, outgoing steam condenses on it and drips down the chimney. After I porridged the chimney, I painted it brick red. Now it's a mess of black dripping trails. This coming spring, the chimney will be painted black.

Planned long term improvements are:

- Adding a few more sections to chimney. I hate the idea of lifting and setting those oversized blocks by myself (over 100lbs if damp), but it is was it is.
- Installing a stainless 6" liner. (I've got to study the in's and outs of that.)
- I have two other stoves, both of which have a lower output.

One of the other stoves might be a better fit for this situation, but I'm leaning toward keeping this one because of it's wood box capacity, it's gorilla sized output, and the potential for sustained sub-zero weather.

Again, thanks to all.
I appreciate your advice and what you're doing for the wood heating community.

 

[kborndale]

Clogging a pipe in 4 months has me thinking your wood is suspect.

 

[begreen]

The wood may not be perfect, but the cold, too large flue + that long horizontal run seem like the core issues. The flue gases are getting slowed down a lot and condensing easily. Changing to an offset with 45s and an insulated liner will dramatically improve performance and reduce creosote accumulation, even with the current wood status.