# understanding upper and lower draft controls and how they work



## aaronmach1 (Jan 17, 2014)

Guys when i understand how somthing works and what it actually does then i get a lot better results. 
Can anyone explain to me how the lower ash pan damper works as opposed to the slider draft damper above the feed door, and then finally the damper in the stove pipe above my wood furnace? (englander 28-3500). I know that they add air when opened etc, but how do the different locations affect the burn differently etc. For example: differences of burning with top slider full open and bottom shut versus top slider half open and bottom damper half open. I just want to understand how to better work them for more effective burns. I guess ill be suprised to see responses to this, i havnt really found any good explaination on it yet. maybe its a learn from experiance only type of thing. Let me know what you guys think.


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## NSMaple1 (Jan 17, 2014)

The damper up in the pipe controls how much draft is available for the unit to use.

I don't like them, as draft the chimney sees constantly varies with weather conditions - therefore you would need to fiddle with it. And there's a risk a windgust could close it up some and create a low-draft condition which might allow smoke & CO to back up into your house. I would replace it with a barometric damper tuned to regulate proper draft. Once it's tuned, it will keep it there.


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## XSKIER (Jan 17, 2014)

On my Hearthstone 1 I get long burn times with the intake air damper opened half way and the flue closed down to about one inch. No excessive coaling either. If I close down the intake air, too many cold coals a few hours later.


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## aaronmach1 (Jan 17, 2014)

but what is the difference in air being introduced above the fire with the above door slider versus air being introduced under the fire with the ash door dial?
Which one affects the fire more and how does it affect it?
The one i really dont understand is bringing in air above the fire with the slider above the feed door.


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## XSKIER (Jan 17, 2014)

I'm not familiar with your englander, but I leave my secondary air tube inlet wide open all the time. Why not get an operator manual for your stove and see what it says?


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## aaronmach1 (Jan 17, 2014)

i not really meaning to sound specific on my model. Im looking for more of a scientific answer i suppose. On how the 2 different locations of incoming air affect the fire quality differently.And which one works better for certain situations.
Like, why does introducing air above the fire help anything? I can see air under the fire helping because heat rises.


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## XSKIER (Jan 17, 2014)

Air below the wood affects the burn rate, air above the wood is for secondary combustion, and the flue damper regulates the volume of Draft.


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## woodchuck357 (Jan 17, 2014)

_The only use , to me, for a damper is to shut off reverse air flow when the stove is not in use or to shut off air in case of a flue fire. The rest of the time it is left open. The draft control below is open and the one above as well as the secondary air are closed when starting the fire and when reducing the coal bed. When starting the fire any draft that does not bring air thru the kindling slows the start up by reducing the air flow where it is needed. The secondary air that comes in from the top is to add air to burn the gases driven out of the wood that don't completely burn at the level of the wood. The draft over the door does help provide secondary air but it's main purpose is to reduce the soot deposited on the glass in the door.
_


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## aaronmach1 (Jan 17, 2014)

thanks guys this helps me understand better!


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## flotek (Jan 17, 2014)

That unit is a bit different on paper theory compared to actual real world settings * if your wood is dry * you want the bottom spin draft just cracked open a half or often just a quarter turn .. The spin draft has a dramatic effect on how much burn time your going to get . The slide should never need to be more than halfway open in my experience . Your draft speed and wood is going to put the settings all over the board . Air from underneath lights off the coals and generally puts out more btu but it eats wood as well think of the slide as the user friendly incoming air it's where the typical range of adjustment should be maintained


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## Whitespider (Jan 17, 2014)

The Englander isn't designed as a secondary combustion furnace… that doesn't necessarily mean it can’t achieve it to at least some degree though. The main purpose for bringing air in the top is to “wash” the glass door and keep it clean. The, clean, fresh air “washing” down over the glass insulates it from soot and creosote build-up. Depending on how the air travels through the furnace before actually entering the firebox, it may also be pre-heated to some degree. That top air is your “primary” air feed… you need it to a certain degree or your glass will eventually turn black.

The ash door spinner draft is a “secondary” or supplementary air feed… you may, or may not need to use it depending on conditions. For (one) example, if you’re burning wood that coals-up heavily, such as elm, hard maple, oak and such, you may find opening that a bit more and closing the top slightly will keep the depth of the coal bed under control. Air coming in under the coal bed will cause it to burn hotter and faster than air washing over the top. It’s a balancing act and sort of a learning curve, what works for your set-up may not work the same with another… don’t be afraid to experiment a bit until you get a feel for what works when.

The flue pipe damper doesn't directly affect incoming air… it limits the outgoing gasses (smoke and heat). It does this by reducing the amount of “suck” the chimney can apply to the firebox. Of course, reducing “suck” will indirectly reduce the amount of incoming air… usually, that is. Often the flue pipe damper can be used to control flue pipe temperature without making drastic changes to the fire itself. It can also increase firebox temperature by reducing heat loss through the pipe, without actually “crankin' up” the fire. Some set-ups need a flue pipe damper to run correctly, some don’t… I always install one because I believe it’s better to have something and not need it, than it is to need something and not have it. My last old smoke dragon flat wouldn't heat unless the flue pipe damper was closed most of the way… I ain’t touched it for the current furnace; it’s been sitting wide-open since day one (I played with it a bit and didn't notice any measurable impact). One problem with a flue pipe damper is you normally need to open it up before opening the loading door or you’ll get a face full of smoke at times. And again, it’s a balancing act and sort of a learning curve… making changes to one affects all three.

If I were you, and if it will run OK without it, I’d leave the flue pipe damper wide open until I got a good feel for the primary and supplementary air feeds. Get comfortable with them before adding the third variable… and then you’ll also have a better idea of how it affects the others, as well as the heating efficiency. If the furnace won’t run OK without it… such as it seems to burn through a cycle way to fast, or maybe ain’t heating like you think it should… then close the flue damper maybe half or two-thirds way and leave it there while you get comfortable with the air feeds. If you start out continuously messin’ with three different controls you’ll just get frustrated… you’ll never really learn how one affects the other… and you won’t be able to duplicate positive results.

Don’t worry, you’ll catch-on to it faster than ya’ think… just look at it as a fun adventure into wood heating.
*


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## brenndatomu (Jan 17, 2014)

Whitespider said:


> That top air is your “primary” air feed… you need it to a certain degree or your glass will eventually turn black.
> 
> The ash door spinner draft is a “secondary” or supplementary air feed… you may, or may not need to use it depending on conditions.
> *


Did spidey just say that you may or may _not_ need air coming in from under the fire?!         Sorry, I'll be back, I gotta go clean my drawers!


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## Whitespider (Jan 17, 2014)

Well, you know me, I ain't about makin' any... "blanket"... statements 
*


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## brenndatomu (Jan 17, 2014)

Whitespider said:


> Well, you know me, I ain't about makin' any... "blanket"... statements, much
> *


Fixed it for ya 

Aaron, my Yukon has both under and over the fire air like yours. I suppose that you will get the best advice from someone who has the same model furnace, but for me, I find that leaving the fire have at_ least_ a small amount (1/2 to 1 turn?) of air from under (ash drawer) at all times gives a cleaner burn. I would think you would want to control the _burn rate_ with the upper control more so. But like others have said, you'll hafta play with it to find the best results from your particular install.
Getting a manometer to check your draft makes it easier to set your flue damper for best results. I have bought (2) Dwyer Mark II (model 25) manometers now, off fleabay for $20 or less delivered to my door. I have mine mounted on the wall next to the furnace, hooked up all the time. As others have said, a baro will give you the smoothest most controlled draft, but a manual damper and a manometer are effective too. A lot of people will say heck with the manometer, but I like to be able to see for a _fact_ what the wind and temperature are doing to my chimney and how my damper adjustments are affecting things, but I'm a tool hound too, so...


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## aaronmach1 (Jan 17, 2014)

guys thanks so much for all the info, very helpful !!! 
Whitespider, good lord! I feel like i need to pay for that much info! Thanks for taking the time to write me a how to book. Ill be rereading that many times tonight. That is better than the answer i was looking for and the idea of not adding the 3rd variable of the flue damper is a great idea and im going to try running it like you describe now! hopefully will shorten the learning curve here. This furnace operates so much different than my old one i cant beleive it. thanks!!!


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## aaronmach1 (Jan 17, 2014)

brenndatomu said:


> Fixed it for ya
> 
> Aaron, my Yukon has both under and over the fire air like yours. I suppose that you will get the best advice from someone who has the same model furnace, but for me, I find that leaving the fire have at_ least_ a small amount (1/2 to 1 turn?) of air from under (ash drawer) at all times gives a cleaner burn. I would think you would want to control the _burn rate_ with the upper control more so. But like others have said, you'll hafta play with it to find the best results from your particular install.
> Getting a manometer to check your draft makes it easier to set your flue damper for best results. I have bought (2) Dwyer Mark II (model 25) manometers now, off fleabay for $20 or less delivered to my door. I have mine mounted on the wall next to the furnace, hooked up all the time. As others have said, a baro will give you the smoothest most controlled draft, but a manual damper and a manometer are effective too. A lot of people will say heck with the manometer, but I like to be able to see for a _fact_ what the wind and temperature are doing to my chimney and how my damper adjustments are affecting things, but I'm a tool hound too, so...


i like the manometer idea. And for that price im going to check one out. Thanks!


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## aaronmach1 (Jan 17, 2014)

lots of them on ebay
http://www.ebay.com/sch/i.html?_odk...w=Dwyer+Mark+II+(model+25)+manometer&_sacat=0


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## brenndatomu (Jan 17, 2014)

aaronmach1 said:


> lots of them on ebay
> http://www.ebay.com/sch/i.html?_odkw=manometer&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0&_nkw=Dwyer Mark II (model 25) manometer&_sacat=0


Many more if you drop the (model 25), just FYI. My search went from 7 to 23 found by doing that...


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## Whitespider (Jan 17, 2014)

aaronmach1 said:


> *Whitespider, good lord! I feel like i need to pay for that much info...*



Heck, don't feel like ya' owe me crap man... really, that's why we're here, to help each other out, share information, and maybe learn something.
We just argue about tires, the EPA, and whatnot when there ain't much else goin' on  it sort'a helps pass the time.
Anyway, just 'cause my post sounds like I know what I'm talkin' about don't necessarily make it gospel for your set-up, ya' still need to do your own experimenting... but I did kind'a keep it as "general" as I could without making too vague to be helpful.

Good luck with it man... and have fun with it‼ Keep us informed on how it's workin' for ya.
*


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## aaronmach1 (Jan 17, 2014)

working very well that last couple hours. flue damper always open 100% ash pan door dial open 1/4 to 1/2 turn and slider above door open 1/2. I put a big peice of red oak in at 5:00 tonight and its still half there and ive added a couple small ash splits around it. Its got me in shorts in here! I think ill have a reds apple ale. (finish the last one, not real crazy about em, kinda sweet)


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## David Wayne (Jan 17, 2014)

The manual for my brunco wood & coal stove says wood burns 80% as a gas 20% as a solid-more air on top. 
And coal burns 20% as a gas & 80% as a solid-more air under the fire.


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## TdiDave (Nov 28, 2014)

brenndatomu said:


> Fixed it for ya
> 
> Aaron, my Yukon has both under and over the fire air like yours. I suppose that you will get the best advice from someone who has the same model furnace, but for me, I find that leaving the fire have at_ least_ a small amount (1/2 to 1 turn?) of air from under (ash drawer) at all times gives a cleaner burn. I would think you would want to control the _burn rate_ with the upper control more so. But like others have said, you'll hafta play with it to find the best results from your particular install.
> Getting a manometer to check your draft makes it easier to set your flue damper for best results. I have bought (2) Dwyer Mark II (model 25) manometers now, off fleabay for $20 or less delivered to my door. I have mine mounted on the wall next to the furnace, hooked up all the time. As others have said, a baro will give you the smoothest most controlled draft, but a manual damper and a manometer are effective too. A lot of people will say heck with the manometer, but I like to be able to see for a _fact_ what the wind and temperature are doing to my chimney and how my damper adjustments are affecting things, but I'm a tool hound too, so...


Question on the use of the manometer. I have burned coal for many years and have a manometer from then. I now have it installed in my wood stove. I had always tried to maintain 0.05 draft with the coal and that seems to be working good with wood as well. Question comes from I have to use the flue pipe damper to get the draft down to 0.05, but obviously the more restrictive I make the incoming air the higher the draft pulls. So if I understand correct I should get a good fire going that I am comfortable with (with flue pipe wide open the draft is over 0.1 at this point) then close it down to 0.05 tomkeepmthe heat in the room not up the flue?


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## brenndatomu (Nov 28, 2014)

TdiDave said:


> then close it down to 0.05 tomkeepmthe heat in the room not up the flue?


Well, I guess that is more or less what's going on. What you are doing is controlling how much air is going through your firebox, therefore controlling the rate of burn, and the velocity of the flue gasses through the stove/furnace. Controlling the velocity, or draft speed, controls the amount of time the hot gasses have in contact with the stove top or heat exchanger. This allows you to dial in for maximize heat transfer. Slower (lower draft) is better to a point, but after that point you are getting a smouldering burn and/or lowering the chimney temp too low...compromise...
-.05" WC is a pretty common standard.

You are checking the draft between the baro and the appliance, correct? If so, sounds like you have a pretty good handle on it otherwise.


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## RMP (Dec 11, 2019)

brenndatomu said:


> Fixed it for ya
> 
> Aaron, my Yukon has both under and over the fire air like yours. I suppose that you will get the best advice from someone who has the same model furnace, but for me, I find that leaving the fire have at_ least_ a small amount (1/2 to 1 turn?) of air from under (ash drawer) at all times gives a cleaner burn. I would think you would want to control the _burn rate_ with the upper control more so. But like others have said, you'll hafta play with it to find the best results from your particular install.
> Getting a manometer to check your draft makes it easier to set your flue damper for best results. I have bought (2) Dwyer Mark II (model 25) manometers now, off fleabay for $20 or less delivered to my door. I have mine mounted on the wall next to the furnace, hooked up all the time. As others have said, a baro will give you the smoothest most controlled draft, but a manual damper and a manometer are effective too. A lot of people will say heck with the manometer, but I like to be able to see for a _fact_ what the wind and temperature are doing to my chimney and how my damper adjustments are affecting things, but I'm a tool hound too, so...



Please tell me where the manometer is connected, and what pressure difference is good. I'm familiar with Dwyer products, but not this application. I suspect one line goes to the flue/chimney and the other to the body of the stove.
Ron


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## jimdeere (Dec 11, 2019)

Open to the room the stove is in. Delta P or differential pressure is your draft. 
Here’s a good read:
https://en.m.wikipedia.org/wiki/Draft_(boiler)


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## RMP (Dec 11, 2019)

jimdeere said:


> Open to the room the stove is in. Delta P or differential pressure is your draft.
> Here’s a good read:
> https://en.m.wikipedia.org/wiki/Draft_(boiler)


Thanks Jim, yes, that's a good article. 
Can you please confirm the connection- the manometer has two ports. In your description, I gather one port simply goes to the room where the stove is installed; the Wiki article says the other port goes to the boiler (Stove, in this case). Are there guidelines for best diff pressure?


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## brenndatomu (Dec 17, 2019)

RMP said:


> Please tell me where the manometer is connected, and what pressure difference is good. I'm familiar with Dwyer products, but not this application. I suspect one line goes to the flue/chimney and the other to the body of the stove.
> Ron


Sorry, just now seen this. Connect one line to the stove pipe, between the firebox and any pipe dampers, the other end to the right port (high) on the Dwyer. The other port/vent just gets left open to atmosphere.
The easiest way to connect into the pipe is to drill a 1/4" hole in the side, get a piece of flexible 1/4" copper tubing, a couple ft. long, bend it into a big S shape. it can then hang from the pipe...get a "1/4" compression to 1/8" FNPT" fitting to clamp on the other end of the copper, then a "1/8" MNPT to barb" fitting to go in the compression fitting...the hose attaches to that...


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## RMP (Dec 17, 2019)

Thanks brenndatomu, that seems straightforward. Are there guidelines for optimal differential pressure?


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## brenndatomu (Dec 17, 2019)

What are you running?
Most wood furnaces call for -0.04" WC to -0.06" WC...but some go as low as -0.03" WC, and some as high as -0.08" WC


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## RMP (Dec 17, 2019)

Quote...What are you running?
Most wood furnaces call for -0.04" WC to -0.06" WC...but some go as low as -0.03" WC, and some as high as -0.08" WC - end quote

Ours is an old (35 years) Thelin-Thompson parlour stove - looks like an upright Franklin. They made two sizes; ours is the larger of the two.


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## brenndatomu (Dec 18, 2019)

RMP said:


> Quote...What are you running?
> Most wood furnaces call for -0.04" WC to -0.06" WC...but some go as low as -0.03" WC, and some as high as -0.08" WC - end quote
> 
> Ours is an old (35 years) Thelin-Thompson parlour stove - looks like an upright Franklin. They made two sizes; ours is the larger of the two.


I have no clue on that one...I'd shoot for the -0.04 to -0.06 range then...unless you have a manual that shows draft specs...doubtful on something that old.


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## RMP (Dec 18, 2019)

brenndatomu,
Thanks for all you help. If i get my manometer installed, I'll try to get back to this forum and comment on what differential pressure seems to work
Happy holidays,
Ron


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