Manual Damper Performance Improvement

Huntindog1 · Dec 21, 2011

I was posting on OldSparks post that his summit wasnt getting above 600 on the stove top. That he would like to get higher on cold nights.

I was thinking about it and posted that maybe his draw was too good, most people think its bad draw but these stoves need to build heat especially up in the top of the stove around the secondaries. I posted that he might try using his manual damper to slow the draw.

Well after posting about that I went home and was experimenting with my stove and the damper. I closed it 3/4 as I was having a little trouble getting it going. I was amazed at the fact that once I closed it 3/4 the stove took off, secondaries kicked in nicely as the temps shot up. I left the intake air wide open with the damper 3/4 shut then I backed the intake down slowly.

So those of you out there that have a manual damper and think you would like a little better performance you might start playing with the manual damper to see if your draw is a little strong and keeping the heat from building up in the stove properly. As this is like tuning a carborator. Air is good but too much cools the box.

BrotherBart · Dec 21, 2011

That is what happens with my stove in the basement on the 33 ft. pipe. If I don't use the key damper I end up with a bunch of fire and not much heat. That tall 5.5" inch liner gets warmed up and it acts like it wants to suck the splits up to the baffle. Close down the damper, watching the fire, and you find that spot where you get a nice burn and more heat.

HotCoals · Dec 21, 2011

I thought the new EPA stoves were not supposed to be used with a key damper.
I learn something new every day here!
Or is this info only referring to tube stoves?

gdk84 · Dec 21, 2011

I agree 100 percent. I often times think that overdraft situations are more overlooked than they should be. Mostly because "well its an EPA stove and doesnt need one" form of thinking. But, it is very important and a very critical part of any wood stove operation. In the oil burner field, draft is very important and we go to the extreme to measure it with every install because every install is different and if it isnt right than you have serious problems. In woodstove world, its a little more forgiving!

Huntindog1 · Dec 22, 2011

HotCoals,

I would say its more for tube stoves as with a Cat stove I would think that its mostly all about getting the smoke exposed to the metal in the combustor. Plus your already reducing the air so much anyways as the cats operate at lower levels.

I have the Flue going from the basement up to like 3 feet above my roof so its like 25 feet of Flue. With that height , I am a candidate for too much draw. Or maybe put it this way "A little bit too much draw" not a bad issue but maybe be able to tweak the stove performance a little.

I saw somewhere a discussion (maybe not on this site) about that a manual damper is not different than restricting intake air. As in If less is going in then less is going out. Unless you have leaks. And in these high efficiency secondary burn tubes stoves there are other holes feeding the secondary air tubes. So this makes me think tweaking the stove by using the manual damper does makes alot of sense especially if you a weird flue setup. As I think these stoves are most likely pre-tuned using a perfect flue setup.

oldspark · Dec 23, 2011

I understand the air in air out thing but not sure why the damper kicks off the secondaries like it does, so far it has not had so much of an effect on the temps although they might be a little better (kinda the same thing with the old chimney) but the burn times seem to be way longer, the stove seems to stay hot way longer. I like BB have a raging fire but only 600 or 650 stove top, not bad but in the morning when the wind has switched and the house is cold I need the extra heat.
Been on this forum for just about 2 years and have learned a lot of good things but you have to take the bad with the good and I did not sort the two out very well, partly due to the fact these stoves were new to me and I did not realize some people on here do not have the best advice. One of the many things that sticks out in my mind was "this stove isn't going to operate like your old one," well guess what, with using the damper I am running it like the old one, I could go on and on but my point is you have to find out what works for your stove and chimney setup.

Huntindog1 · Dec 23, 2011

I think the reason secondaries fire off quicker when you close the manual pipe damper , from my observation on my stove, is that it lets the heat build in the top better. It maybe slowing down the smoke as it travel to the top of the stove at the same time this slowing means the heat is residing in the top of the stove longer. Plus more time the smoke spends up there maybe just a few micro seconds longer means better chance to burn it. But your trying to find a sweet spot with the damper. Not to damper too much. I find 3/4 closed works pretty good for me. All setups are different and some people may not need to use the damper. I wish I new what all the air holes were doing in my stove as I have 2 in the back sides underneath that I think go up to the secondaries then I have one up front center under neath that is just like a 3/8 or so round hole that maybe feeds the primary dog house air that is front center just under the door inside. Then I have the slider at the top that covers some slots that is my main air control that I think the air from this slider control comes in thru my front air wash. But how its all interconnected inside or are they all separated that is what I don't know. My guess is that they are all separated. But thinking of this setup you can kind of see how using a damper in conjunction with the slider air control makes for another dynamic of burn control.

oldspark · Dec 23, 2011

One thing is for sure, the control over the fire is amazing, anyone having over fireing issues or just control problems need to try one, still need to keep an eye out for bad gaskets and leaks as always but well worth a try. It sure lookks like I will be using less wood now. Knock on wood

, this is the first time I have been impressed with the amount of heat for the wood used since I bought the stove.

pen · Dec 23, 2011

oldspark said:
One thing is for sure, the control over the fire is amazing, anyone having over fireing issues or just control problems need to try one, still need to keep an eye out for bad gaskets and leaks as always but well worth a try. It sure lookks like I will be using less wood now. Knock on wood , this is the first time I have been impressed with the amount of heat for the wood used since I bought the stove.

What took so long to try this!?!

Glad to hear it is working better.

pen

oldspark · Dec 23, 2011

pen said:
oldspark said:

One thing is for sure, the control over the fire is amazing, anyone having over fireing issues or just control problems need to try one, still need to keep an eye out for bad gaskets and leaks as always but well worth a try. It sure lookks like I will be using less wood now. Knock on wood , this is the first time I have been impressed with the amount of heat for the wood used since I bought the stove.

Click to expand...

What took so long to try this!?!

Glad to hear it is working better.

pen

I tried it before and it did not seem to do much for the stove top temp (as now it still slows down around 600 to 650) but the amount of wood consumption has went down, having the house heat easier has happened before (even with the old stove) and then it seems to change again so we will see. I was hammered about the damper when I put it in last winter with the old chimeny and so many do not use them I just sort of farted it off. These stoves are god's gift to the world ya know and they need no help from such a simple thing as a damper. :cheese:

iceman · Dec 23, 2011

This is so funny, I was just thinking about oldspark!
I am glad it worked for you! I was watching my stove go over 700 and thought maybe you use big splits.. mine are med-small and get high temps and long burns ... When I use big ones I never go over 600 but get longer times at 300
Then I found this an the spark is now a happy fire! Lol
Happy Holidays

oldspark · Dec 23, 2011

iceman said:
This is so funny, I was just thinking about oldspark!
I am glad it worked for you! I was watching my stove go over 700 and thought maybe you use big splits.. mine are med-small and get high temps and long burns ... When I use big ones I never go over 600 but get longer times at 300
Then I found this an the spark is now a happy fire! Lol
Happy Holidays

I have had the stove up over 700 a few times and I always think I have found the answer but the next time I do not get the same results with the same kind of load, my 788 temp was with small pieces of Oak so will continue to try different things now that I am using the damper.

spirilis · Dec 23, 2011

In terms of overall airflow an MPD is no different from tuning the air damper, except in EPA stoves where the intake damper usually doesn't adjust the secondary air supply--for those, short of covering up the plenum where the intake air comes in, there's no way to control that, unless you can control it at the flue with an MPD or even a Barometric damper. Also, echoing Huntindog1's point, having excessive airflow through the burn tubes could cool them down too fast (in addition to sending what little heat your fire's producing straight up the chimney), and slowing that airflow with the MPD may account for the reason the secondaries come online so well. That's something I don't think too many people think about...

So I think regardless what they say, if your chimney is fairly tall (i.e. >20-25ft I guess) it's a good idea to have an MPD. You can always just leave it open all the time, and they're not that expensive...

MarkinNC · Dec 23, 2011

I'm having a hard time getting my head wrapped around the physics of "keeping the heat in the stove." I would be interested to know the temperature of the chimney above the key damper before and after closing is? It would seems the less air you exhaust, the less air is pulled in for combustion. Don't get me wrong, I'm not being contrary and saying it does not work. I have a 15 foot chimney system and can literally start a fire in 60 degree weather without a problem. If my stove has an issue is that it is hard to run below 600.

So I guess I am intrigued. Is it a lot of work putting a key damper in an existing double wall pipe?

I apologize if I took this thread off topic.

spirilis · Dec 23, 2011

The MPD is mainly a consideration for folks with excessive draft. If you have a 15 foot chimney, I wouldn't even bother.

When the draft is utterly excessive, well beyond what EPA certified stoves are tested for (see http://www.gulland.ca/florida_bungalow_syndrome.htm), it's entirely possible that so much air rushes through the secondary burn-tubes that those burn tubes never get hot enough to ignite secondary combustion, and so that extra air entering the upper firebox doesn't serve to generate extra heat (as it normally should) so much as it serves to cool down the flue gasses from the burning wood. Net effect, air passing under the stovetop is significantly cooler than it should be, the stove doesn't heat up like it should, and the flue is probably cooler too. And you're wasting wood... The fire might be lively but it's entirely driven by primary air (which should be pretty good, unless you've turned it down all the way). Probably no ghost flames coming from the secondaries too.

The whole secondary combustion effect is a goldilocks thing (needs to be "just right", as smoke/etc. requires extremely high temps to ignite)... stoves use refractory insulation under or over their baffles to help concentrate the heat around the burn tubes to make it adapt to a wider range of scenarios, but if you've got such volumnous amounts of air going through that it can't get hot enough to light off, there's not much you can do except slow it down with an MPD or somehow narrow the intake plenum underneath or behind the stove where the air comes in.

LLigetfa · Dec 23, 2011

There are so many factors that vary not only by stove but also by flue, by wood, and by operator. My stove is an insert and so don't have a key damper on the flue. For years, the wife and I were opening the combustion air too much, thinking that more air = more heat. It was very counter-intuitive to turn down the air to get more heat but we found the sweet spot. I also modified the zipper air inlet to be able to control it. Less is more!

oldspark · Dec 23, 2011

LLigetfa-my stove temp has never climbed up like many people claim here, it will to a point and I understand less is more but mine does not work that way, I have wild secondaries and the craziest fire you could imagine but my stove likes 600 to 650 or so. I think some times it is hard to get your point accross that you have tried every setting in the book and it still does what it does.

MarkinNC · Dec 23, 2011

spirilis said:
The MPD is mainly a consideration for folks with excessive draft. If you have a 15 foot chimney, I wouldn't even bother.

When the draft is utterly excessive, well beyond what EPA certified stoves are tested for (see http://www.gulland.ca/florida_bungalow_syndrome.htm), it's entirely possible that so much air rushes through the secondary burn-tubes that those burn tubes never get hot enough to ignite secondary combustion, and so that extra air entering the upper firebox doesn't serve to generate extra heat (as it normally should) so much as it serves to cool down the flue gasses from the burning wood. Net effect, air passing under the stovetop is significantly cooler than it should be, the stove doesn't heat up like it should, and the flue is probably cooler too. And you're wasting wood... The fire might be lively but it's entirely driven by primary air (which should be pretty good, unless you've turned it down all the way). Probably no ghost flames coming from the secondaries too.

The whole secondary combustion effect is a goldilocks thing (needs to be "just right", as smoke/etc. requires extremely high temps to ignite)... stoves use refractory insulation under or over their baffles to help concentrate the heat around the burn tubes to make it adapt to a wider range of scenarios, but if you've got such volumnous amounts of air going through that it can't get hot enough to light off, there's not much you can do except slow it down with an MPD or somehow narrow the intake plenum underneath or behind the stove where the air comes in.

That is a good explanation that makes since. If the air velocity in and out of the stove (say in cubic feet per minute) is high, the air is unable to get super heated enough for optimum secondary combustion. I can wrap my head around that. I think chimney output is pretty significant, as would be air intake, which is why I got an OAK.

oldspark · Dec 23, 2011

Just want to add it did not do anything for my top end so far. :mad:

HotCoals · Dec 23, 2011

I know with my stove the damper seems to make little or no diff.
I'm afraid of cooling the flue to much by using it...I'm very low most of the time as it is.

oldspark · Dec 23, 2011

HotCoals said:
I know with my stove the damper seems to make little or no diff.
I'm afraid of cooling the flue to much by using it...I'm very low most of the time as it is.

Not sure they are a good idea with the cat, does not seem to lower my flue temps any at all.

HotCoals · Dec 23, 2011

oldspark said:
HotCoals said:

I know with my stove the damper seems to make little or no diff.
I'm afraid of cooling the flue to much by using it...I'm very low most of the time as it is.

Click to expand...

Not sure they are a good idea with the cat, does not seem to lower my flue temps any at all.

I concur ..I just could not take it out when I installed the cat stove.
Way to many years of having to use it with the same stove without a cat.
I just don't use it now.

HotCoals · Dec 23, 2011

oldspark said:
LLigetfa-my stove temp has never climbed up like many people claim here, it will to a point and I understand less is more but mine does not work that way, I have wild secondaries and the craziest fire you could imagine but my stove likes 600 to 650 or so. I think some times it is hard to get your point accross that you have tried every setting in the book and it still does what it does.

Maybe I'm nuts but I never hardly ever see or need 600-650 stove top temps.
That's getting pretty hot imo.
I seen 700 once and I almost had a pucker moment!

If your house is heating fine what would be the problem?

EDIT: Wouldn't 700 stove top be about 1400 inside the box?

Rich L · Dec 23, 2011

Without my pipe damper I was getting 5-6 hours of heat from my Mansfield.With the damper I getting 12 hours of good heat.I also have a powerful draft.

oldspark · Dec 23, 2011

HotCoals said:
oldspark said:

LLigetfa-my stove temp has never climbed up like many people claim here, it will to a point and I understand less is more but mine does not work that way, I have wild secondaries and the craziest fire you could imagine but my stove likes 600 to 650 or so. I think some times it is hard to get your point accross that you have tried every setting in the book and it still does what it does.

Click to expand...

Maybe I'm nuts but I never hardly ever see or need 600-650 stove top temps.
That's getting pretty hot imo.
I seen 700 once and I almost had a pucker moment!

If your house is heating fine what would be the problem?

EDIT: Wouldn't 700 stove top be about 1400 inside the box?

Well I have a lot of south windows and when it gets cold with a south wind I need the extra heat, other wise for the most part it is fine. My old stove had the ability to put out a ton of heat if I needed it. An example would be last night, no wind about 10 outside house was 70 with only 4 pieces of wood so I let the fire go out, wind came up and switched to south, not good woke up to 56 degrees, so I needed heat and needed it now. That is really the only time the summit will not heat the house very well, I could hit 700 or even 750 for a short period of time I believe it would help a lot. A lot of Summit owners are hitting 700 to 800 stove top temps with out a problem and yes I believe that is 1400 inside the box at least but you have to have a high temp for the secondaries to work.

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