A better explanation...

[Chris-PA]

I had a hard time understanding it also WoodHeatWarrior, until I put the newspaper “smoke bomb” inside the pedestal where the air enters. I could watch the smoke reverse direction and head out the flue well before it made it to the bottom of the box… the overdraft just makes the flue a huge vacuum cleaner. By changing the stove draft control, or the flue damper, I could make the smoke go a little lower, or higher, in the box before it reversed… but it never made it to the coals. I played around with it for most of a morning and just couldn’t get it to work. In my case the draft is so strong that no matter how I tweak, the draft just over powers the inlet… I can’t get the relationship between intake and exhaust to balance properly.

When it gets really, really cold and my draft goes wild… it pulls the incoming air out before it can get to the fire, and sucks any heat being made right along with it. And pulling the heat out just compounds the problem… it becomes a charcoal maker. It doesn’t matter where things are set; the relationship of incoming to vacuum can’t be balanced. The only way I can see to change that (and I’ve tried everything else mentioned, plus more) would be to open the holes to the primary air (not the main hole where air enters the stove intake system, but the holes where air actually enters the firebox chamber) to increase velocity/volume in relation to the draft (at any given setting)... but heck, that could make things worse. The problem, and my fear is, the stove would way over-fire… especially during warmer weather with a somewhat reduced draft. Another option would be to place a restriction in the top of the chimney… but then there’s the possibility of smoke filled house during times of reduced draft. And besides, right or wrong, I have an appliance shared chimney… I have to be extremely careful about chimney modifications (admittedly, that does place limits on my options to some degree).

I should add... what few coals are kept live is only because of the "pilot", or "boost" air because when i plugged that problem got much worse... I found complete unburnt splits under the coal bed.

Maybe a shorter explanation would be that the extreme over-draft is turning my firebox into a vacuum chamber.

I understand your smoke bomb test, but where the visible smoke travels to and having enough oxygen to burn are not necessarily the same thing. I think the idea of it turning the firebox into a vacuum chamber is going too far with the idea. It can be at no lower than the atmospheric pressure in your basement.

You have also said that you get giant jets of flame from the secondary air outlets (was this with the primary wide open?), and I think this is a clue. Without the means to limit secondary air, combined with a strong draft, it's gonna burn like crazy up top. The airwash/primary might be getting sucked right up the flue before it gets to the bottom as the outlet is right there. So then you have lots of secondary air and effectively even less primary air as it is not getting to the bottom. If that is the case then with that much draft the primary air setting becomes irrelevant. The burning top of the load may bury the lower logs in ash pretty fast.

As for the flue damper - it does not change the static pressure differential much at all (that is based on the temperature difference), so up to the point where it begins to restrict flow it doesn't do much. I assume if you messed with it constantly you could hold it at the right spot, but as you said it is unlikely to stay there long. I suspect it would do much better if you could make a secondary air control.

With a stove where both primary and secondary are restricted together then at least the secondary cannot blast the top with too much air. The burning would be more controlled and longer and the heat would not be pulled out the flue too fast as the total air flow through the stove is restricted.

I would bet that the exact shape and location of the primary air ducts is probably quite important, ans the performance of different stoves under those conditions may vary a lot.

Last, these stoves were intended to have the air controls adjusted at least somewhat during the burn, so I doubt they will work the way you want them to.

And finally, I apologize - I was wrong in saying your system had no draft and that your mods may the the problem, as it sounds like there is a design deficiency. I also apologize for my tone.

 

[Whitespider]

You have probably already talked about why you haven't tried this before...

Yes I have, and in this thread actually.
A quick recap...
Besides the obvious, such as massive amounts of unnecessary (warm) air being pulled from the house, I have an appliance shared chimney... and that, along with the varying demands of a wood-fired appliance would make it's operation erratic at best. Although it might still be worth a try, our extreme cold weather (and for the most part, my extreme over-draft) is now gone until next January... the time for experiments is past. I have a different wood heater sitting in the shop, of different design feeding air under a grate where it will be forced up through the coals (basically an air-tight furnace, not an EPA type stove). It will be installed sometime this spring, long before cold weather rolls back around. This thread is now mostly informational... I'm no longer looking for solutions to the current set-up.

 

[Whitespider]

I think the idea of it turning the firebox into a vacuum chamber is going too far with the idea.

Just using that as an analogy.

 

[Whitespider]

You have also said that you get giant jets of flame from the secondary air outlets (was this with the primary wide open?), and I think this is a clue. Without the means to limit secondary air, combined with a strong draft, it's gonna burn like crazy up top.

Like I've said, the stove has one control lever that operates the two separate primary and secondary gates at one time. I did disconnect the secondary from the primary and messed around with it a couple of different times... I could make it better, not great, and it required constant adjustment as conditions changed. Finally I went with the best option... I modified the linkage so the secondary gate was closed more (in relation to the primary gate) than the factory setting. Completely closing the secondary after the secondary burn shut down seemed to help a little, not much, with temperatures in the teens... but made no noticeable improvement when temperatures dropped into single digits.

That's when the problems become ridiculous, single digit temperatures... and down-right stupid when it dropped below zero. At temps around zero, with the wind blowing, I could get the metal of the firebox hot for maybe 45 minutes, then the fire would collapse into a bed of coals, the secondary would shut down, and within a few minutes you could lay your hand on the bare metal. No matter what I tried, no matter how much I messed with it, it would just stop heating. The only thing to do, if we wanted to stay warm, was feed more wood to it, which increased the size of the coal bed until I had to shovel out the box... and most of the coals I was shoveling were dead, or near dead.

I think most of you can understand my frustration level after two months of that... right? I even contemplated shooting the darn thing with my .44 :hmm3grin2orange:

 

[brenndatomu]

Yes I have, and in this thread actually.
A quick recap...
Besides the obvious, such as massive amounts of unnecessary (warm) air being pulled from the house, I have an appliance shared chimney... and that, along with the varying demands of a wood-fired appliance would make it's operation erratic at best. Although it might still be worth a try, our extreme cold weather (and for the most part, my extreme over-draft) is now gone until next January... the time for experiments is past. I have a different wood heater sitting in the shop, of different design feeding air under a grate where it will be forced up through the coals (basically an air-tight furnace, not an EPA type stove). It will be installed sometime this spring, long before cold weather rolls back around. This thread is now mostly informational... I'm no longer looking for solutions to the current set-up.

Sorry, I guess I missed it somehow.
There is very little if any warm air pulled from the house if you install a make-up air pipe ending near the BDR. (path of least resistance) Putting a J trap on the end of it keeps the cold air from flooding the basement.
A shared chimney makes no difference if the BDR is installed directly on the wood furnace flue pipe. It's gonna hold a steady, automatically regulated draft on whatever is upstream from it. It would have been an interesting experiment, just sayin...
Anyways...I actually agree with your current theory. And, I'm sure you and the Mrs. will be much happier with the new furnace.

 

[Whitespider]

And finally, I apologize - I was wrong in saying...

It's all good... always has been...
Besides, it's never just one person's "fault", I'm fully able to recognize my part in creating "friction"... my apologies extended to you also.

 

[slowp]

Have you ever considered beefing up the insulation in your house?

I have a 3 year old "bungalow" style house...1400 square feet. My stove is beyond the national EPA requirements. Our state went with more restrictions. My house is well insulated and fairly air tight. It has small vents that pull in fresh air when a fan goes on.

The Quadrafire Millenium stove was installed by the dealer. It draws in air from a hole in the floor which is piped into the stove. The chimney is pipe, and probably right around that 15' heighth. Our winter climate temps average just above freezing, but we can get cold snaps. I'd call it mild.

The stove works fine. In fact, I usually let it go out or just put in enough wood to keep it warm. Otherwise, the house is too warm.

My friends have a built in the 1980s house. Their's is two story and has a daylight basement. It is super insulated and designed as a passive solar house. They had trouble with their new WA EPA certified stove smoking. The dealer--same as mine, came out and the problem was the chimney. Their chimney is brick and stone. They put out the big bucks to have it relined, and they no longer have smoke. They have a woodstove in the basement AND a woodstove upstairs. The upstairs stove is the new one. I think their house is about 2000 sq. ft. and they burn 4 cords a year--mostly Doug fir. They keep their house too warm. They are at a higher elevation than me. I'm at 1000 ft. they are at 1500 and yes, that 500 feet is a difference out here.

We're not all unhappy and the stoves do work in our cases. Their case is interesting. They were ready to travel to Montana or Idaho to get a non-WA certified stove, but it seems their chimney was the problem.

Like most folks here, we mostly burn softwoods. That's what is easily found. I guess I don't understand this coaling thing. I get glowing coals, which throw out heat, and turn into ash. That's what I thought fire did.

 

[Whitespider]

Have you ever considered beefing up the insulation in your house?

Sure... and I'm doing that a bit at a time, and I seal-up potential drafts before winter.
I'm not seeing how that would fix the stove problems though, like it going cold when all logic says it should be hot... but...

We're not all unhappy and the stoves do work in our cases.

I'm in no way arguing that... or discounting it.

I guess I don't understand this coaling thing. I get glowing coals, which throw out heat, and turn into ash. That's what I thought fire did.

Which should help you understand the frustration I've been experiencing.

 

[Steve NW WI]

The more I read, the more the dim bulb in the back of my mind is lighting up - scary, I know!

What I think is going on is that under "normal" draft conditions, the intake air has enough density and or velocity to reach the bottom of the stove and burn down the coal bed. At high draft, the air isn't allowed down far enough to reach the coals, instead just sucked straight out the stack.

Here's a crude drawing to help illustrate what I'm saying:

While I'm thinking more and more that the baro regulator would fix this problem, and likely some of the others' similar problems, I personally think they're a "band aid" solution. Dumping cold air up the chimney just seems wrong to me. I don't have a better idea, yet - gimme some idle time and a few cold ones and something might come to me.

I LIKE it when we can get back to trying to think through problems rather than slinging barbs at each other. There's a lot of sharp minds on here, and someone is liable to come up with a better mousetrap.

 

[slowp]

I still don't get the frustration with coals. What part am I missing? Wood burns, turns into glowing coals, then the coals burn down into ash....right? It is a normal process. The coals throw off heat too. The ash is ash. I can't see how any stove could not do that. Cleanout of the ash totally depends on what is burned.
Our native maple makes a lot more ash than our Doug-fir. I don't see any stove brand changing that.

When I burn slash, I get coals and ash. What am I missing that causes this to be abnormal?

 

[Steve NW WI]

When I burn slash, I get coals and ash. What am I missing that causes this to be abnormal?

Part of it is the fact that without enough air, those coals will sit there for a good long while. Go out to a burn pile 2, 3 days later and barring rain, it won't be hot next to it anymore, but a little raking around will still find a bunch of coals under there.

 

[Chris-PA]

I still don't get the frustration with coals. What part am I missing? Wood burns, turns into glowing coals, then the coals burn down into ash....right? It is a normal process. The coals throw off heat too. The ash is ash. I can't see how any stove could not do that. Cleanout of the ash totally depends on what is burned.
Our native maple makes a lot more ash than our Doug-fir. I don't see any stove brand changing that.

When I burn slash, I get coals and ash. What am I missing that causes this to be abnormal?

This is what I think is the issue. I don't mind a good bed of coals, it radiates a lot of heat. But if that bed of coals is in a fire brick lined stove covered with a thick layer of ash, then it is sealed up and not radiating much. The reduced oxygen will let it cool off and smoulder. I think the strong draft and lots of secondary air from the manifold above the fire is burning the top of the load fast, and covering the bottom logs with ash.

Slowing down the secondary air and reducing the burn rate should prevent this, but not all stoves give any control over the secondary air.

 

[brenndatomu]

The more I read, the more the dim bulb in the back of my mind is lighting up - scary, I know!

What I think is going on is that under "normal" draft conditions, the intake air has enough density and or velocity to reach the bottom of the stove and burn down the coal bed. At high draft, the air isn't allowed down far enough to reach the coals, instead just sucked straight out the stack.

Here's a crude drawing to help illustrate what I'm saying:

While I'm thinking more and more that the baro regulator would fix this problem, and likely some of the others' similar problems, I personally think they're a "band aid" solution. Dumping cold air up the chimney just seems wrong to me. I don't have a better idea, yet - gimme some idle time and a few cold ones and something might come to me.

I LIKE it when we can get back to trying to think through problems rather than slinging barbs at each other. There's a lot of sharp minds on here, and someone is liable to come up with a better mousetrap.

It does seem wrong, I agree, but it works. And I have had zero chimney/draft issues.
BDRs probably work the best, or at least make the most difference with tall or high draft chimneys.
They sure are nice for those wild weather days. Large temp swings, wind, etc.

I'd say your drawing is exactly right Steve. Basically, by lowering the draft, your are slowing it's velocity through the stove, allowing designed air flow patterns to take place in the stove, and it gives the heat some residence time inside the stove/heat exchanger/stove pipe so that the heat has time to transfer to the house instead of zipping up to meet your chimney cap.

A properly installed/adjusted BDR allows you to run your wood burner in its "sweet spot" all the time. And, it's almost impossible to overfire the stove too...

 

[Jredsjeep]

i cant say for sure but if i had to bet i think adding a restriction in the intake could be detrimental to the fire. you would be putting the fire box in a vacuum condition where would reduce the amount of air burned but be far more likely to flare up if the door seal is not perfect or when you open the door.

i know a barometric draft might not be the most ideal inside the house but could it be fed by an outside air source so its not pulling the warm air out of your house? it would just be sending the cool outside air up. that can create some separate problems though such as creosote like mentioned.

i imagine your chimney drafts even better if you have some wind going, and from what you describe it is fairly windy in your location. a little bit of fluid or air flow equations can show that. is your chimney outlet located at the peak? could the wind passing over your house be creating a low pressure area sort of like the wing of an aircraft?

do you have a chimney cap with a screen at all? i am wondering if that could help slow things down. i am far from an expert and just throwing out some of the more crazy idears i got besides the standard ones that have been mentioned.

maybe you need a bi-metallic strip linked up to a butterfly valve located at the top of your chimney to regulate the flow according to outside air temperature.:hmm3grin2orange:

 

[Whitespider]

L.O.L.
I'm lovin' the drawing Steve, but ya' forgot the air wash/primary, so I added it in red.

It's super easy to tell where the air wash/primary is reversing direction by looking at the glass on my door.
The bottom two-thirds is now a white milky, translucent color... the glass is permanently etched because it wasn't getting the cooling effect of the air wash.
When I got that thing it had been used a few years, yet the glass was crystal clear... and it stayed clear right up until the cold weather and operational problems started.
The transition from clear glass to etched glass is exactly where the newspaper smoke reversed direction during my "smoke bomb" test... which was very enlightening, the upper third (or maybe a bit more) of the firebox filled with thick, rapidly swirling, grayish-yellow smoke, the lower two-thirds barely even turned hazy... and even that took a couple of minutes before it did.

 

[mooseracing]

I still don't get the frustration with coals. What part am I missing? Wood burns, turns into glowing coals, then the coals burn down into ash....right? It is a normal process. The coals throw off heat too.

I can't heat the house because of the coals. IF I try to run the stove at mid level heating capacity all that happens is I end up with 8-12" of coals. I can't put wood in, the coals aren't giving off enough heat but to keep the stove steel at about 200 degrees. I burn on low and get an 8hr burn, there's less coals but not enough heat on the cold days. The secondary air needs to be blocked once the secondaries aren't burning, then the air can come in the bottom and burn the coals.


The cap with a screen doesn't change a thing for me. I removed mine.

 

[Whitespider]

Jredsjeep,
Brick chimney, about 20-22 inches (don't remember exactly now) square on the inside, wide open at the top, about 5 feet above the peak of a hip roof, protruding through the roof at a hip junction.

 

[slowp]

This is what I think is the issue. I don't mind a good bed of coals, it radiates a lot of heat. But if that bed of coals is in a fire brick lined stove covered with a thick layer of ash, then it is sealed up and not radiating much. The reduced oxygen will let it cool off and smoulder. I think the strong draft and lots of secondary air from the manifold above the fire is burning the top of the load fast, and covering the bottom logs with ash.

Slowing down the secondary air and reducing the burn rate should prevent this, but not all stoves give any control over the secondary air.

OK, I don't have that happening. I have ash on the bottom, then a layer of coals on top, and it radiates a lot of heat through the front of the stove. Wonder why it doesn't happen here? Oh well...

My stove has an air intake below the door. Maybe that helps.

 

[Chris-PA]

OK, I don't have that happening. I have ash on the bottom, then a layer of coals on top, and it radiates a lot of heat through the front of the stove. Wonder why it doesn't happen here? Oh well...

My stove has an air intake below the door. Maybe that helps.

I don't have it either. If I stop it down too far I'll get lots of coals but they're exposed. If I open it too far I'll get a hot fire and nothing but ash. It's a 30' insulated SS flue inside a large stone chimney.

And yes, if I open the door when I have it stopped down and burning well it sure does flare up.

I think the difference is:

1. Lots of draft
2. Insufficient control of secondary air intake
3. Variations between stoves.

 

[Steve NW WI]

L.O.L.
I'm lovin' the drawing Steve, but ya' forgot the air wash/primary, so I added it in red.

Thanks for adding that - it was something I overlooked. The results still come out about the same. What might help some others understand what I'm starting to get here - note what happens when the overdraft is sucking that cool air out the top. Instead of heating the top plate of the stove, where a big percentage of the heat radiates from, the cool air is actually cooling down the stove, lending credence to Spidey being able to lay his hand on a stove full of coals.

Bits and pieces, but they're all starting to fit together in this puzzle.

Just throwing this out FWIW - the tall stack probably has a lot more to do with this than the basement install. I'd guess it's operate similarly if installed on the main floor in the same flue. I have a short chimney - 13 1/2' from the pipe exit about 2' below ground level to the top of the clay tile liner - and a basement install works well for me. Draft is almost never a problem for me - I get flow up the chimney even when it's cold and the flue pipe isn't connected, but without measuring tools, I don't think it's excessive.