Author Topic: "Airtight" wood stove operation  (Read 39910 times)

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(unknown)

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"Airtight" wood stove operation
« on: March 08, 2010, 11:01:38 AM »
First, I finally learned the name of my 70's or 80's  era woodstove: it's simply an "air tight" design.   The stove has two air inlets that I can shut and allow absolutely no air inside the stove:  those are located on the right hand side, one about 3 inches from the bottom and the other maybe about 4 inches from the top.


-There is also a key damper on the pipe flue.

-There is also an electric fan to push hot air toward the room.


I've always used wood to heat in winter, and so has my father, grand father, etc...


Now, I've been doing some reading and I'm not sure we're doing this "the right way", especially for "night time" heating.


We typically always leave the top air inlet completely shut and only use the bottom air inlet to control the rate of fire.  


At night, we would typically load the stove with a lot of wood, leave only the minimum

air entry possible and close the key damper on the pipe flue to slow down the burn even more.  We would also stop the fan, because running it seems to make the wood burn too fast.


The goal here is to make the fire burn slowly enough that:

   -Fire warms the house through the night

   -I can have an 8 hours sleep and wake up to a small bed of coals, making it easier to start a new fire.  


Experience shows that this typically works, in that I do wake up to some coals, but the house is also very cold.


Browsing around the internet tells me that I should change a few things in the operation of my stove:

   -Never use the key damper on the flue pipe.  It is completely useless on an air tight stove

   -Slow burning fires are more polluting and less efficient that hot burning fires.


Here is what I understand from this:

-I should leave the key damper open at all time and never touch it ever again.

-I'd be getting more heat from my load of wood  and waking up to a warmer house if the fire lasted 4 hours instead of 8.  This means opening the air inlet more.  Con:  This means no more nice bed of coal in the morning to start my fire on.


Did I get this right?

Do people really get 8 hours fires from a load when burning a "hot fire" ?   This seems like a long time to me.


Thanks!

Simon


--------------

Sources :

http://www.woodheat.org/tips/biglistoftips.htm

http://www.woodheat.org/q&a/qaoperation.htm

« Last Edit: March 08, 2010, 11:01:38 AM by (unknown) »

Stonebrain

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Re: "Airtight" wood stove operation
« Reply #1 on: March 08, 2010, 01:19:10 PM »
I'm heating on wood for most of my life.

I understand the dillemma.


I'm quite happy now with my scandinavian stove.

The good thing with this stove is that I can regulate seperatly the air that coming from underneat that goes through  the grill and the coal,and the air that's coming from above the fire.And you can shut the gril


So,for starting the fire you open the air from underneat and the gril.When the fire is hot you close the gril and you close the inlet from below.During the day,as long as you put in more wood the fire keeps on flaming and being hot,but because the fire is closed from below a good amount of coal is formed.

Then the evening,you wait till the last wood stopped flaming.Then you close it completely.

If there is only coal the fire can go on very slowly without polluting.

In the morning the house is quite cold because the stove didn't heat very much,but the stove is still warm and there is still enough coal.


So  in the morning if you open the air from beneath and open the grill(moving the grill to free the passage for the air) the fire start very fast and you can put bigger wood right away.


I don't know about your stove but for my stove this works perfectly.


good luck with it!


cheers,

stonebrain

« Last Edit: March 08, 2010, 01:19:10 PM by Stonebrain »

cardamon

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Re: "Airtight" wood stove operation
« Reply #2 on: March 08, 2010, 03:20:00 PM »
Yes the dilemma of burning wood....  I have never had a damper in the flue and not really sure what the purpose of those are, I guess to slow down the burn if your stove is not tight enough.  I guess it could be argued that it slows down heat loss up the flue be convection.  The "experts" say that a proper wood burning set up should not create smoke and if it does than something is wrong with either the equipment, method or both.  However that is a load of crap in practice because the price you pay for a smokeless fire is a lot/too much heat and/or a fire that you have to babysit all the time.  I have a a very oversized stove that I ran damped way way down and it will go three cold days on one load of wood.  Makes more creasote sure but its not an issue with a properly done chimney.  I have commented on this issue recently and also said that I think the ideal way to burn wood is with a whole bunch of thermal storage, then you can run it hot like it wants and store up enough heat for 5 days or whatever you design for.  Of course that is not easy to retrofit a system like that, really needs to be built from the ground up.
« Last Edit: March 08, 2010, 03:20:00 PM by cardamon »

morglum

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Re: "Airtight" wood stove operation
« Reply #3 on: March 08, 2010, 07:01:33 PM »
Thanks Stonebrain for the reply.


question though: I'm not sure what kind of grill you are talking about?  (probably is a language issue)


Cheers

Simon

« Last Edit: March 08, 2010, 07:01:33 PM by morglum »

nick1234

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Re: "Airtight" wood stove operation
« Reply #4 on: March 08, 2010, 07:43:17 PM »
when i changed to an air tight a few years ago i found the operation quite different than a simple fire box

about a hour before going to bed for the night i load the air tight up and give some air till the wood is burning good then close every thing tight the wood seems to gasfie red coals no flame the stove pipe cools down after a while it will not burn my hand

 but the stove is quite hot the instructions that came with the stove said no damper and avoid bends in the pipe

 mind goes strait up and  trough the roof the pamphlet said it breaths thought the exhaust pipe chimney thats why its not very hot  

 in winter the fire rarely goes out as long as there are medium size coals going i just add wood close tight

 i only let it go out when i have to clean out the ash about a mouth

and i only wood heat  

 and that is the way my air tight works


nick

« Last Edit: March 08, 2010, 07:43:17 PM by nick1234 »

morglum

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Re: "Airtight" wood stove operation
« Reply #5 on: March 08, 2010, 08:08:48 PM »
thanks everyone!

« Last Edit: March 08, 2010, 08:08:48 PM by morglum »

fabricator

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Re: "Airtight" wood stove operation
« Reply #6 on: March 09, 2010, 04:42:25 PM »
Your research has you on the right track, you want to play with the stove until you get a more straight time/temperature line, you want to get it less spiky, cold,hot,cold,hot.
« Last Edit: March 09, 2010, 04:42:25 PM by fabricator »
I aint skeerd of nuthin.......Holy Crap! What was that!!!!!
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WoodstoveWizard

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Re: "Airtight" wood stove operation
« Reply #7 on: March 10, 2010, 05:14:09 AM »
I tried to reply to this last night but it got swallowed by the netgremlins.


It sounds like your stove is of the old fashioned design - operated as you describe it will be very inefficient and polluting as you are not providing enough air to burn the gases given off. A large portion of the energy in you firewood is going straight up the chimney unburnt.


You describe two different air vents on your stove - it may be that one of these provides external air to the upper part of the stove, which will help burn the wood gases more effectively - open this a little and observe your smoke stack to see what effect it has.


Ideally you want to balance both air supplies - the bottom air which supplies the embers and the top air that supplies the burning gases - so that combustion is stable.  You want just enough bottom air to keep the embers hot (which cooks the wood and drives off wood gases) and just enough top air so that the wood gases burn cleanly.  Too much of either and the fuel will burn too quickly, too little and it will be polluting and inefficient.


Modern "EPA Approved" stoves have been carefully designed to burn wood cleanly without smoking - they are more efficient and less polluting but do need more regular fuelling and generally cannot be made to "stay in" over night.  If you want to wake to a warmer room you could consider switching over to a thermal mass stove of some sort.


SAFETY NOTE

The damper in the flue itself should never be closed, and if possible should be locked open or removed completely. Damping down the fire with this vent may cause combustion gases to back up into the living space - carbon monoxide is odourless and highly poisonous in even small quantities.


Dampers such as you describe are no longer legal in most places due to the possibility of misuse, but they are still in a few old installations.


Overall I suggest you experiment - find an "efficient" compromise an possibly give up on a full 8 hour burn.


All the best,


Mike

« Last Edit: March 10, 2010, 05:14:09 AM by WoodstoveWizard »

morglum

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Re: "Airtight" wood stove operation
« Reply #8 on: March 10, 2010, 07:03:29 AM »
Very interesting, thanks Mike.


Guess it's time to retire the flue pipe damper and start using the top air inlet then..


Cheers

« Last Edit: March 10, 2010, 07:03:29 AM by morglum »

TomW

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Re: "Airtight" wood stove operation
« Reply #9 on: March 10, 2010, 07:54:11 AM »
I claim no status as an expert.


I grew up with wood heat folks heated with a coal stoker furnace and after about say 6 or 8 years old it was my chore to see the coal feeder chain was kept full of appropriate chunks.


Subsequently I heated with wood my whole adult life except a winter in a warmer climate.


After a lifetime of burning cordwood I will share with you a couple of things I believe:


To properly burn wood cleanly and get the most heat you need to let it get plenty of AIR. Choking off the air supply will indeed extend burn time but allows a lot of unburned fuel [gases] to escape to the atmosphere. This creates smoke and gunks up the chimney and has led to the demise of many inattentive would be wood heat users.


Heating with wood is NOT cheap or easy. After you put your sweat into gathering, cutting, stacking and seasoning firewood it just seems stupid to not get the heat out of it that is in  it.  


My personal wood burners have ranged from an open hearth stone fireplace [major fuel hog] to my current stove 30 years or something old and capable of being closed up enough to extinguish the fire. A couple stoves I used leaked so much air they lit the room at night through the cracks. That type never needed a chimney cleaning because they supplied enough [too much] air to the fire so it burned clean and hot. These required a flue damper to control the air going through the system. I also think it helps retain some heat that would otherwise go up the flue. This heat retention is obvious if you stand there and go from damped to open with a well burning fire.


I still use the flue damper on the current stove that is more or less "air tight" it vents to a Class A clay lined masonry chimney. I find this same heat retention seems to be there. If I am not careful this stove is prone to gunk up the chimney if you pinch off the combustion air too far with a load of even bone dry wood. We use hardwoods like Elm, Oak, Hickory, Hackberry and Cherry exclusively cut and dried at least a year in the open shed so it is dry.


If I were to build a stove it would include an afterburner air inlet to assure full combustion in a smoke chamber at the top of stove. Or just go for a down drafter that draws flue gases through the coal bed before it exits.


But, the very best way would be a massive built in unit with multiple small flues like 3" pipe running through a mass of material to  the flue. Burned hot and fast I believe this would be the very best method for a ground up heating system for solid fuel.


Well, there it is, rambling but my thoughts. Likely not what everyone believes but there you have it.


I do like heating with wood. Do not be fooled into thinking it is a free heat source.


We own and maintain 2 Stihl Chain saws, [a 16" and a 20"], a pickup, an ATV and trailer, a wood splitter. As well as consume a fair bit of fuel, oil and chains. All for the "free" heat from our "free" 400+ acre timber.  Takes a good few hours of real work to do, also but I wouldn't do it any other way, as long as I am capable.


Tom

« Last Edit: March 10, 2010, 07:54:11 AM by TomW »

morglum

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Re: "Airtight" wood stove operation
« Reply #10 on: March 10, 2010, 08:52:37 AM »
Thanks Tom for the tips.


hehe, I agree that it is far from free.  


But man do we love doing it.  Every winter we are kind of sad when we have enough wood cut and need to find another reason to waste time in the woods. Good thing maple syrup season is usually only a few weeks away by then.


"People love chopping wood. In this activity one immediately sees results."

-Albert Einstein

« Last Edit: March 10, 2010, 08:52:37 AM by morglum »

carbethhutter

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Re: "Airtight" wood stove operation
« Reply #11 on: March 11, 2010, 12:30:05 AM »
I have allways found it is better, to burn large diam. slices placed in top of each other, for a controlled over night burn,instead of narrow diameter long logs, less area exsposed to the air.
« Last Edit: March 11, 2010, 12:30:05 AM by carbethhutter »

downdrafter

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Re: "Airtight" wood stove operation
« Reply #12 on: January 28, 2014, 05:24:59 PM »
greetings, my first post. this is an old thread I'm compelled to reply to. "airtight" design in respect to wood or coal stoves, doesn't mean sealed off entirely from the outside air.  it means the only way air can get in, is through the specific above fire and below fire draft controls.  on some stoves these are both adjustable.  on others only the below fire draft is adjustable, and the "above fire" secondary air is fixed slits or holes, that cannot be adjusted.  that is how my Harman Mark I coal stove is.  the above fire air is typically used for "secondary combustion" i.e. to burn off the volatiles, by-products, i.e. burn the smoke and gases from the primary burn below it.  yes it is true, as designed many wood stoves burned wood FROM THE TOP DOWN, and burned coal from the bottom up.  I spoke to Harman techs and engineers and they said, top draft can be shut completely when burning coal.  bottom draft can be shut completely when burning wood, and just top draft used- I've done it already.  but with coal the fixed above-fire slits in the Harman fire off the methane above the coal fire itself.

airtight stoves are better than the old unsealed stoves.  the old stoves leaked a lot around the windows and doors.  the doors didn't even have gaskets on them.  the primary function of the manual flue pipe damper, was to control the burn rate from the exhaust flue side, rather than precisely from the primary air draft side on the front of the stove.  it made sense as everything being burned should exit via the flue pipe.

slow it down too much though, and the smoke will find a way out elsewhere, through the front of the stove.

Mary B

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Re: "Airtight" wood stove operation
« Reply #13 on: January 29, 2014, 03:49:43 PM »
For the few years I burned wood in an airtight stove I resigned myself to getting up twice during the night to add wood, or damp it down and let the furnace run. Now that I have a pellet stove I just make sure the hopper is full and go to bed  ;D

SteveCH

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Re: "Airtight" wood stove operation
« Reply #14 on: January 30, 2014, 08:01:17 PM »
I have an older [25 yr.] RAIS WITTUS which has air intake controls for both the lower fire bed area and the upper stove box area. As a couple of others have said, the lower intake is for combustion air to get the fuel going. The upper intake is to provide additional air to aid in burning off the gases before they can exit the stove up into the chimney.

On my stove, the way the burn works best, and the way RAIS designed the stove, you close off the upper intake and open the lower for starting the wood burn and establishing a good fire. Gradually, I close off the lower intake and open the upper as the hot gases develop. Eventually, the lower intake is almost completely closed once the fire is good and established, lots of coals and so on. Even when I add wood, this control stays almost closed off. As in, probably 95% or more closed. The upper intake gradually becomes completely open, it helps burn off the gases and also provides adequate oxygen to keep the burn going.

This works great. Burning off the gases not only cuts down on pollution, but it also provides additional heat oxidizing those gases. Quite a bit of heat. This is what the newer catalytic stoves are doing, too, burning off gases and cleaning the exhaust plus gaining more BTUs from the same amount of wood, BTUs that would be lost as the gases go up the pipe and out into the atmosphere. The catalytics probably do a much more thorough job of dealing with those gases, and they also combust the particulate matter in the exhaust.