Running a wood stove

[dug]

So I got my wood stove up and running but I am having a little trouble getting it to burn well. It is a Vermont Casting Aspen and I know several here on this forum have this model so I was hoping for some tips.

I am having problems getting the fire to run hot enough to burn all the fuel and run efficiently. It seems to draw well and starts up very easily. After building up the fire and closing the door everything looks good and I can see what looks to me like lots of air flow and good combustion with nice lively flames. However after 15 minutes or so the flames die down and it turns into a slow lazy fire with little or no flame, and not a lot of heat. A lot of unburned material remains and I have to stir it up and re kindle it to bring it to life again. Leaving the door cracked a hair seems to help the ignition greatly so I'm assuming there is an air flow problem. This problem continues even after running it for several hours and developing a good bed of coals.

I bought the stove used but it looks in good condition and I cleaned it thoroughly. I am leaving the air inlet in the back open for now until I can figure out how to get it to burn hot enough to close it down some. I have heard Mt. Don talk of the benefits of the fresh air intake and plan on installing it later if possible (can that be routed through the floor?), but I wouldn't think that could be a problem now as my house is not sealed up and still has open venting.

The wood I am using is about 70% juniper, 20% pinion pine, and 10% scrub oak. Not ideal I realize but it is very dry (at least 2 seasons), split, and what is available on my property.

Being a total rookie I did a lot of homework before installing my chimney and thought  had all my bases covered, but looking over the owners manual for my stove yesterday I read that you should use no more than 8 ft. of single wall pipe above your stove because above that the smoke will be cool enough to cause creosote  buildup problems. I wonder if that could also cause draw problems but like I said the draw seems really good to me.   I now have about 16 feet of single wall pipe going up to the roof. I didn't see this information in other sources I read, is it a major concern?

I need to get a thermometer so I can get more accurate information and I see they sell ones that mount on the stove pipe and some that rest directly on the stove. Is one better than the other? Both?

Any suggestions much appreciated!

[MountainDon]

Thermometer. I use a Harbor Freight infrared thermometer. There's is about as cheap as they come. I paid $30 but that was a few years ago. I like it as it can be used to measure the temperature of a lot of things. The one I have may be off by a few degrees. It reads a few degrees high when I compare readings to those from other thermometers... pot of water, wall surface and so on. But that's not a big deal, there's not much difference in getting a reading of 212 or 218 when reading the chimney pipe.

http://www.harborfreight.com/non-contact-laser-thermometer-96451.html

[MountainDon]

I totally missed that tidbit on the maximum recommended length of black pipe (single wall) above the stove. Perhaps having an 8 foot ceiling height blinded me to that.   That could be contributing to the burn issue I suppose. The temperature of the pipe drops considerably as the pipe reaches our ceiling.


The fresh air kit will do wonders for the burn. At least it made all the difference with our installation. I did not install it right away as I was in a hurry to get the stove installed and working. Our initial burns were somewhat disappointing too, until I opened a nearby window. That made a big difference. I too tried leaving the door open a crack but was rewarded with a smoky interior smell. Burning with the door open also interferes with the secondary burn.

After I installed the fresh air kit the stove operated very differently, much better. True, our cabin was not "air leaky" at that point.

You should be able to run the fresh air feed through the floor. The vent kit uses 3 inch diameter vent pipe. I used flexible aluminum vent.

[John Raabe]

Dug seems to have no problem getting a fire started and hot initially (when the chimney is cold) - that is the time my stove is most likely to have draft problems.

But once the stove and chimney are warm and the stack effect is pumping air, a wood stove would normally fully combust all the fuel - even when you close it down. Mine does.

Is there something changing after the fire is going? Is there a very cold exposed chimney above the roof?

[MountainDon]

Ash tray clear enough? The primary combustion air flows under the bottom grate and up through the slots cast in the grate. That was the source of the problem oljarhead had with his.


And just FYI, the secondary burn air flows through the stove sides, between the cast iron outside wall and the firebrick. Then it flows up and through the cross tubes under the upper firebrick. There it mixes with the wood gases and loops over the upper firebrick at the front and flows to the chimney exit at the rear. It burns more in the upper chamber. The round spot on the stove top reaches 500 to 700 degrees when a good burn is happening.

[dug]

But once the stove and chimney are warm and the stack effect is pumping air, a wood stove would normally fully combust all the fuel - even when you close it down. Mine does.

Is there something changing after the fire is going? Is there a very cold exposed chimney above the roof?

I have 16 ft. of single wall pipe going into a 6 ft. section of class A pipe with 3 ft. exposed above the roof. It hasn't been real cold yet, 27 last night.

Ash tray clear enough? The primary combustion air flows under the bottom grate and up through the slots cast in the grate. That was the source of the problem oljarhead had with his.

Yes, I have been emptying it regularly. I have been fooling around experimenting with different burn methods today. Using small sticks up to an inch or so in diameter I can create a nice hot, sustaining fire. It stays very active and the stove throws out a lot of heat, and if I crack the door just a tiny bit I can raise the heat to inferno levels. With the door closed you can see and hear good air movement inside. The stove pipe on the lower section gets nice and hot, about what seems right to me, but the section near the top is obviously much cooler. Still pretty warm but I can put my hand on it pretty much indefinitely.

When it was still good and hot, I added 3 or 4 pieces of very seasoned oak and juniper split to about 2 in. diameter. That was about 1/2 hour ago and it is still burning fairly well but kind of lazily, not as active as I think it should be and not much air movement visible inside. Also it has cooled noticeably on both the stove top and pipe.

If I use larger wood, still split and not too large, I can not maintain a very hot fire unless I crack the door a bit. In a short time it ends up smoldering and producing very little heat, and little to no flame even though there is plenty of fuel. Like a dying campfire before turning in at night.

I was thinking more that maybe it does have something with the long stove pipe cooling towards the top but as John said it seems to draft well right from a cold start, using small wood.
I also tried a running a fan directed at the rear intake as Don suggested but it did not seem to make a lot of difference, though the wood did eventually burn more completely.

I am going to continue looking into the matter and appreciate any and all suggestions. 

[Shawn B]

Dug,    Maybe you should check the thermostatic air damper. I remember Mtn. Don having problems with his stove and had to adjust the "chain" on the damper. Now I think Don was having over heating problems caused by too much air and had to adjust the damper closed more. They way he described it was one of those ball style chains as used on rubber sink stoppers. Maybe your damper is closed too much when it thermostatically closes and you need to lengthen the chain by a ball or two.  Hopefully I am remembering this right......chime in Don.

[MountainDon]

I made an adjustment to the chain length to drop the door to be more closed. That helped getting the burn lowered a tad. That will also permit more creosote production, but it does not seem to be an issue.

[dug]

Insert Quote
Dug,    Maybe you should check the thermostatic air damper.

I have been fiddling with that, not sure I have it right yet. For now I have been manually propping it wide open with a little piece of metal. Looking forward to when I need to close it down due to too much heat.

[LeoinSA]

Prior to divorcing/remarrying/moving to SA I heated exclusively with wood for about 20 years in two different houses.  As a kid we heated the house primarily with wood.  Shops and garages were also heated with wood.  A few places I've worked were wood heated.  So let's call it 30+ years experience.  As always, other folks may find they get different gas mileage than I do. 

The various fire containers I've personally used ranged from a 55 gallon barrel stove - both single and double - a Vermont Castings Defiant http://www.vermontcastings.com/products.asp?model=defiant and a fireplace insert similar to this one - http://www.regency-fire.com/Products/Wood/Wood-Inserts/H2100.aspx.  The insert was a double box design and a fan ran to circulate room air around the firebox.  We heated over 1400 square feet with this and the only time we fired up the whole house furnace was when the temps dropped to below +10°F.  That happened only once or twice a year where we lived at the time.

Combustion air does not have to get to the fire from below.  From in front or along the sides is adequate.  In fact you'll get more complete combustion and a much longer lasting fire if 1) you're burning a wood that is slow burning and 2) if it will form a bed of coals and the combustion air is not disturbing the integrity of said coal bed.  Obviously you burn what's available in your area and the most common/inexpensive may not meet these two criteria.

It's been my experience that creosote does not come out of the stove exhaust gasses unless it meets a very cold pipe.  It'll condense on that cold pipe faster than you can say 'snap'!  Inside the cabin would not (IMO) be cold enough to cause that.  Looking at the pics you posted it seems that you have double wall pipe on the exterior so you should not have a problem. 

You made mention of the pipe being cool to the touch up higher - I'm making the assumption you mean near the ridge line inside the house.  I would not call it normal for single wall pipe.  But it may not be abnormal either.  It's my experience that one should not be able to keep skin contact for more than a split-second with single wall pipe within 8'+ of the exit from the firebox when there is a substantial fire going.  A damped fire OTOH may not put out enough hot exhaust to more than warm the pipe 2' from the firebox.

Draw is another kettle of fish.  I've found that stoves draw best if the exit point is 36" or more above the roof that is within 8' to 10' of the chimney - like in this diagram - http://www.fireplacesnow.com/smchinfo.asp.  From the looks of your installation pics you've got that covered.

Tightness of the structure will play a major role.  If there is - in effect - a vacuum being created by a tight structure, nothing else you do will have any major effect on the fire.  Don's correct that an outside vent kit will make a huge difference - and the fact that it will put outside air directly into the firebox and not 'pollute' the warm inside air is another plus.

As to the appearance of the fire.  Ya don't need raging flames to get complete combustion.  There is a balance between air and combustion that can only be found by living with the particular stove for a heating season or two.

Were it me, I would get a damper similar to this - http://www.amazon.com/GRAY-METAL-PRODUCTS-7-CID-DAMPER/dp/B001EF9PRY.  I've found that this addition will allow the air intake to be open wider thus allowing more air into the firebox while keeping the fire from becoming too hot and overheating the home.  YMMV applies here in particular.

Other than burning seasoned wood, you've got a distilled version of what I know - maybe ain't much, but hell, I'm officially 'old' so I can have my senior moments and forget stuff with the best! 

[John Raabe]

Sounds like good advice to me!

[MartyM]

I may be stating the obvious, but wet wood acts the same way.   It needs a lot more air to burn and leaves a lot of unburned wood.   

You said your using well seasoned wood?  Is the stack off the ground? Do you cover your wood pile from rain and or snow?  I had a stack on my deck over the summer for my fire pit, split and dried over a year.  As the temps dropped I used it in my stove for the first few burns of the heating season. Very slow cool fires, But toss in a few splits from the wood shed and she roars to life.

Just a thought. 

[dug]

LeoinSA-

Thanks for the wisdom and advice. As you say it may take some time for me to season to this particular stove.

I plan on installing the fresh air vent but I don't think that is my problem now, as my house is completely uninsulated and loose as a goose. I'm not really looking for raging flames but am trying to develop an active, sustaining fire that burns completely. One that seems alive rather than dying. Right now I am struggling to maintain a fire that is hot enough and I don't think the pipe is as hot as it should be. I feel like I would rather be fighting to slow the burn rather than the other way around. What I think would be my best wood, oak, is the hardest to burn and seems to just go out, even if the fire is hot. This same wood goes up like a fireworks factory in the outdoor fire pit. I have a lot to learn.

I am going to get the damper.

You said your using well seasoned wood?  Is the stack off the ground? Do you cover your wood pile from rain and or snow?  I had a stack on my deck over the summer for my fire pit, split and dried over a year.  As the temps dropped I used it in my stove for the first few burns of the heating season. Very slow cool fires, But toss in a few splits from the wood shed and she roars to life.

It is not covered but with the weather here in NM it stays very dry. Hard to describe but it makes that distinctive sound when you knock two pieces of really dry wood together.

[LeoinSA]

One more important point.  If the stove itself is designed to heat a space larger than what you actually have you will never be able to have a substantial fire without overheating the space.  The only way I know to counteract that is to keep a small fire that needs tended much more often.  This could be your issue - not cold enough outside to warrant a 'active' fire or a stove that's too much for your space.

[LeoinSA]

It is not covered but with the weather here in NM it stays very dry. Hard to describe but it makes that distinctive sound when you knock two pieces of really dry wood together.

I hated to split wood.  I loved to split wood.  Love/hate - hate/love.  One of the most satisfying sounds is when it's below zero and the maul causes the chunk to fly apart - almost explode!   The sound of that round or quarter coming apart in the cold is indescribable - but oh so satisfying.

[dug]

One more important point.  If the stove itself is designed to heat a space larger than what you actually have you will never be able to have a substantial fire without overheating the space.  The only way I know to counteract that is to keep a small fire that needs tended much more often.  This could be your issue - not cold enough outside to warrant a 'active' fire or a stove that's too much for your space.

I don't think that's the issue, it's a pretty small stove and I've yet to come close to overheating the place. I'm going to pull it apart again tomorrow and see if maybe there is something wrong that I missed.

I hated to split wood.  I loved to split wood.  Love/hate - hate/love.  One of the most satisfying sounds is when it's below zero and the maul causes the chunk to fly apart - almost explode!   The sound of that round or quarter coming apart in the cold is indescribable - but oh so satisfying.
Posted on: Today at 05:51:13 PM Po

I can relate to that. I was splitting wood today and it is a great feeling when you hit your mark and the wood flies. I miss the cold, and the sound of the cold here in the Southwest

[MountainDon]

dug, I do believe the issue you are having relates to the length of single wall pipe more than anything else.

"There should be no more than eight feet of single-wall
stove pipe between the stove and a chimney. Longer
runs can cool the smoke enough to cause draft and
creosote problems. Use double-wall stove pipe for
longer runs." .... p.25

I don't recall reading that before, but as I said before my ceiling is only 8 feet high and I probably mentally discarded that info because of that.

[cordwood]

 I have had and seen many older wood stoves that worked just fine with much more than 8' of single wall pipe inside the heated space. I tend to run as much as I can just for the added heat transfer I get from the pipe. Our friends have a newer VC (?!model?!) that has at least 16' of 8" single wall with about 4' of horizontal run half way up and it seems to work as well as most of the newer EPA stoves I have been around. Since we cook on our stove a lot I don't care for the multi chambered, Catalytic converter, CARB approved, Latest and greatest type stoves. They may work great in some situations but they have never proven their worth in my experiences. I can boil 5 gallons of water on my old Fisher. Our air washed glass fronted, multi layered Century wouldn't boil a pint. Before I got the firebricks in the proper alignment it wouldn't burn newspaper completly. I may burn more wood with my dinasour but when I want it hot,....It will get HOT! It's hot right now! Time for coffee !

[MountainDon]

I figure VC must have a good reason for recommending no more than 8 feet of single wall pipe.
In addition to the 8 foot rule quoted above, there is...
"In cathedral ceiling installations, extend the prefabricated
chimney downward to within 8 feet (2.4m) of the
stove".

There is also a recommendation that from flue collar to top of chimney should be 16 feet.

Why does VC have all these rules? Because under EPA emissions rules they can't make the stove work right unless those criteria are followed. That's my guess at least. There is no doubt in my mind that it was easier to make a wood burning stove when there were no rules. I've owned pre-1990, non-EPA wood stoves. They worked with little fuss and bother. But we have to deal with what we can buy these days.

FWIW, air dropping from 500 degrees F to 170 degrees F decreases in volume by about 62%. So as the smoke from the fire cools going up the long single wall pipe it takes up less space and slows down. I think that relates to the problem at hand. Because of that my personal belief is that adding a chimney damper will not improve matters at all in this situation.

The VC Aspen will bring a large pot of water to a rolling boil. We've done that many times. Boils so fast the lid rattles with escaping steam.

[dug]

dug, I do believe the issue you are having relates to the length of single wall pipe more than anything else.

You may be right. Wish I had a way to test that theory before scrapping what I have and buying double wall pipe. What about wrapping the upper sections with fiberglass insulation? Just for a test of course.

[MountainDon]

I'd thought of that. As long as the paper doesn't touch the pipe it may work.


Let's compare our two systems with the exact same stove. assuming the stoves are both correctly assembled and that both have sufficient air supply, mine by direct duct and yours by virtue of it still being air leaky, what are the differences.

I have about 5 feet of 6 inch diameter single wall pipe from the stove chimney collar to the 12" of insulated pipe that hangs below the ceiling.  Above the ceiling it is all 6 inch diameter insulated pipe up to the chimney cap. I have 8 feet of insulated pipe above the ceiling. Overall pipe length is about 14 feet. That's 2 feet short of the VC recommendation. I tried that with the thought I could add 2 to 3 feet if necessary. One reason I postponed that was the longer stretch of pipe above the roof would have required roof stays or guys.

When we leave the cabin for home, if there is still some fire in the stove I scrap everything together in a pile, open the draft all the way and let it burn out. We we return there is usually a pound or so of not fully burned charcoal left, and a tray of ashes. Burning 100% pine with a little DF mixed in. Outside seasoned for a couple years now. I have some stored through the summer in a couple of wood bins (no rain no snow on that wood). Some of the wood pile, the part that will see us through the winter is covered with strips of metal roofing material to keep most of the rain and snow off.


You have ample overall chimney length. The real difference is with the extended run of single wall pipe.

Does your chimney cap have a screen? If it does there's an outside chance it is fouled, not letting the smoke through like it should.

Do you have the elbows installed or is this a test setup with a straight up run like mine?

[dug]

Does your chimney cap have a screen?

I'm not really sure. I didn't notice one when I put it on but I wasn't looking for it either. Not too fired up to scale that roof again, maybe I will see if I can get a decent look with my binoculars tomorrow.

Do you have the elbows installed or is this a test setup with a straight up run like mine?

It's a straight run right now.

I wrapped some R19 fiberglass around the top 8 ft. of the pipe today and am going to light it pretty soon and see if that makes a difference. I'll let you know.

[dug]

Well I tried insulating the top portion of the pipe and it made no difference. I took it apart again today and blew compressed air through the air vents. Nothing much came out except a little fine ash and I ran a water pipe snake through to confirm they were open. I was not sure if I fixed anything but I got to know the air flow of my stove well.

Anyway I lit a fire and got it good and hot, then threw a couple of logs in and shut the door. To my amazement they caught flame immediately. Success! 

An hour later now it is still burning strong and the stove is nice and hot. Yea!!

[John Raabe]

Glad to hear the stove is now working properly... It's a bit of a mystery what the blockage was but you seemed to have cleared it.

This is good.

[LeoinSA]

Was the stove sitting idle outside for a time?  Maybe some mud dauber wasps (or something similar) got into the passages and partially clogged them?  Dunno.  Just guessing.