Old smoke dragon driving me nuts !

kwikrp said:

I have an old VC defiant early 80's. I am using well seasoned hardwoods as well as bio bricks and a few pieces from pallets. This is what happens from a cold start takes several hours to get to 400*. I basically keep throwing in wood and burning with the primary and secondary wide open and even the door a crack open. If not the fire will smolder and temps will be around 200*. To me it seems like there is a air supply restriction. I took it apart last year resealed it and cleaned out the back of the fire box. I can take a flashlight and shine it through the primary and secondary and I can see light entering the fire box! I have a 25 ft masonry interior chimney with 8 x 8 clay flue. It was cleaned in Sept of '09. Have check no blockages or obstructions.Well once I can get stove over 500* it is great heats well. But the battle is exhausting to get the stove top to that point.
Is it possible that the chimney is taking so long to heat to create a strong draft? I have observed that sometimes with the doors a crack open that the doors begin to be sucked in a bit. I also have taken a lit cigar (cohiba) and have opened the doors to the stove and have help the cigar up to 8 inch away and the smoke goes horizontal and up the stack. Maybe to much draft I dont know. Any help or thoughts would greatly be appreciated.
I have also observed that on occasion when I open the air supplies one would think that I would be heading towards an over-fire, but just the opposite happens the temp begins to drop.

Click to expand...

Do you have a pipe damper?

Because, if your wood is dry, the stove is in good condition, and your chimney isn't choked down with creosote, you might have a strong draft and a lot of your heat is going out the chimney.

Secondly, have you tried playing with the air control. Sometimes 'wide open' isn't the best method for getting the stove hot.

kwikrp said:

I also have taken a lit cigar (cohiba) and have opened the doors to the stove and have help the cigar up to 8 inch away and the smoke goes horizontal and up the stack.

Click to expand...

Wait a minute, are you burning in updraft mode or horizontal mode?

kwikrp said:

no pipe damper manual says not to use one

Click to expand...

You might want to give a pipe damper a try. I have one on the Vigilant and it works well.

I was told I might need a flue pipe damper in a similar situation, but so far it seems to be working for me. 25' interior masonry chimney, basement installation, but only a 7" x 7" tile liner. With an 8" x 8" liner, you are even more of a candidate for one. Look at it like the thermostat on a car engine. When it's partly closed more heat stays in the block. How do you know if you need one? Put one in, and if it works... you needed one.

As far as the fire dying when you open the intake air all the way, that really depends on how big a charge you got going in there. If the stove is full and already raging in updraft mode, I can't imagine opening the intake all the way will slow the fire down. But if you have a smallish fire burning in horizontal mode, you are adding more air than you need for the fuel and all that will happen is that the chimney will pull the excess air through the fire and cool it down. Again, with a strong draft and no key damper, the only thing restricting air from passing through the box is a reduced intake opening. I've been getting better burns by inching that thermostat lever over to the right after the secondary is underway and watching the result on the pipe thermometer five minutes later.

From a cold start... are you building the fire slowly or are you trying to get big stuff on too soon? I always take my time with several small kindling splits and only add a new piece when the last one is fully involved with flame. Lots of folks here say they start with a few big pieces on the bottom and build the fire on top of that. I don't doubt them, but logic tells me I want vigorously burning wood directly in front of those intake holes. That always works in my Vigilant. Your stove is very similar so I imagine it would work in yours as well.

You seem to be doing everything right, so this is a puzzler. I think it's pretty unlikely that you have too much draft - the opposite seems the problem, especially if your very dry wood just sits there and smolders producing smoke but little heat. This is a sign of too little oxygen. If the stove were over-drafting, you'd find the wood gone when you open the loading door. A couple of things to check: put your hand by the opening with the thermostatic flap cover. You should be able to detect the draft even with no fire in the stove. The same is true of the opening below the loading door. Check these two things with the damper open and closed. Since you rebuilt this stove and cleaned behind the fireback, I'd say there must be blockage somewhere in the chimney or stovepipe. This can happen with amazing speed under the right conditions.

At first I thought the same, but:

kwikrp said:

Have check no blockages or obstructions.

Click to expand...

Then there's this:

- I have a 25 ft masonry interior chimney with 8 x 8 clay flue.

- I have observed that sometimes with the doors a crack open that the doors begin to be sucked in a bit.

- I also have taken a lit cigar (cohiba) and have opened the doors to the stove and have help the cigar up to 8 inch away and the smoke goes horizontal and up the stack.

- Is it possible that the chimney is taking so long to heat to create a strong draft?

Click to expand...

I'll assume the cigar trick was done with a cold stove. And I personally would use a Padron Anniversario instead of a Cohiba, but....

All of these things indicate at least an adequate draft to me.

The strength of the static draw of a chimney is dependent upon height and flue gas temps, not flue wall temps. If you have flue gas temps of 630ºF at the collar (from what folks are finding out here, about 400º 18" up on a single-wall pipe using a magnetic thermometer) and an outside temp of 30ºF (600º difference) you should have an average flue gas temp of about 300ºF, giving you a static draw of about .1" of water in a 25' tall chimney (according to my wood burning "bible"). That is considered to be an adequate draft in most installations. How hot are your flue temps running during these troublesome starts?

Anyway, I'd check again for any possible blockages. Draft is not the same as flow, and you seem to be having a flow problem. In a crude analogy, draft is kinda like the voltage in a system and flow is like the current. You can't force a lot of current past a tight restriction. You need bigger wire. Since your "wire" is already the recommended size for your stove (8" flue), I'd start to look for restrictions to the flow. Don't forget to look inside your firebox. The way you are loading at startup can have more of an effect on your burn than marginal wood or poor draft. Any changes in wood type, split size, moisture content, charge size, or timing could make a passable startup procedure get downgraded to a poor one.

A couple of other thoughts: What happens when you start the fire and leave the loading door and damper open? If you're getting a good fire then, I'd say there is no chimney or stove pipe blockage. If, on the other hand, even with the maximum possible amount of air available, you find only a smoldering fire, there has got to be some obstruction in pipe or flue.

If you get the fire going, what happens if you close the loading door but leave the damper open? It is perfectly normal to have to leave the damper in an open position until you feel some heat coming from the stove when starting cold. This can take up to an hour or more when everything including the chimney is cold.

Finally, your comment about leaving the loading door open a crack is intriguing. If you find it necessary to do this to ignite whatever you're using to start the fire, then I would suspect - unlikely as it seems - that the wood is not dry enough or there is serious blockage. Leaving the door open a crack produces a very powerful concentrated draft (and can easily warp castings if you're not careful); you should not need to do this to start a fire.

Everything still seems right and the wood is obviously not the problem, but it's pretty clear that the fire is oxygen starved. So... (And apologies if you've already done all this).
Check the chimney once again for obstructions. Easy if you use a mirror through the chimney's cleanout door.
Take off the stove pipe and check it. Once it's off, check the area behind the fireback, too.
Make sure the little cast iron cover is not blocking the opening on the loading door side.

One thing I'm not clear on. Has the stove been like this all winter or has the problem developed over time? If it's been like this from the beginning, I'd suspect some sort of blockage in the air flow path inside the stove as a result of something that went wrong during the rebuild. An area where this could conceivably have happened is around the metal mesh and stove cement arrangement that forms the channel between the fireback and rear casting. This could also have broken off and plugged things up at some point if the stove originally worked ok after the rebuild. If, on the other hand, things have gradually gotten worse and worse, we're back to gradually accumulating blockage, most likely in the chimney.

The Defiants have extremely strong draft, especially when they are in damper open/updraft mode - that's why they were very good at handling less than perfectly dry wood. With decent wood, but certainly not as dry as what you're using, I never remember having to wait more than an hour to get to a 500+ surface temperature with the damper open, so there is definitely something amiss.

How many biobricks? They're incredibly moisture sensitive and I ended up with a few bad smoldering batches. They should go up like torches. If not they're wet.

Is this a slammed installation (no liner at all)? If so, you are probably getting terbulant airflow. Add 15' of liner and see if there is an improvment

Everything points to too little draft - not too much!

Although the chimney seems good at first look....let me ask some other questions....

8x8 chimney? Often, the interior measurement of such a chimney is 7" x 7" - sometimes much smaller. That means the chimney is a reduction in size from the Defiant 8 inch.
Height? Where are you measuring the height from? Is it from where the pipe goes in?
How many elbos (turns) on the stovepipe between the Defiant and the chimney?
Are all the pipe and chimney connections well sealed with furnace cement?
Does the chimney have a cold air "sump" which extends way below where the stove enters the chimney?
Is there a cleanout door on the chimney....is it well sealed close?

These things can end up being death by 1000 cuts.

As an example, let's project that the Defiant would work great with a 20 foot straight up chimney (these stove do need a strong draft!).
If you have two els, that takes 10-12 feet off the effective height of the chimney - so now your chimney is 10 feet.
You are slightly downsizing, now your chimney might be 9 feet.
If your pipe joints leak and a cleanout leaks, that might make it 8 feet....

Now you can see where the trouble starts! There is a LOT of info about this kind of stuff in the QA and in the articles section...as well as here.

Webmaster said:

8x8 chimney? Often, the interior measurement of such a chimney is 7" x 7"

Does the chimney have a cold air "sump" which extends way below where the stove enters the chimney?

Is there a cleanout door on the chimney....is it well sealed close?

Click to expand...

As for my installation... Guilty, guilty and guilty.


I have a 4' sump that goes down to the cleanout door. I've often wondered about its effect on my draft. Can that be temporarily sealed off somehow? How do you seal the cleanout door better? It seems rather flimsy to use gasketing material. Do these two thing make a significant difference?

On flue size, the original VC literature recommends an interior masonry chimney as the ideal chimney, and specifies a 8x8" nominal size liner. My 8x8" liner has a measured 7x7" inside diameter. That is 49 sq.in. compared to 50 sq.in. for 8" round pipe... a negligible difference IMHO. However, I was told that since smoke spirals as it rises, my 8x8" (7x7" ID) square clay-tile flue only has the flow characteristics of 6" round pipe? I've never been able to find a table for that. What is your opinion?

Also, in order to gain access to the inside of a 8x8" flue, you need to have a 8" round thimble. But a 8" nominal size thimble has a 7" ID. This creates a flow restriction at the thimble. I run 8" pipe straight up to a single 8" elbow and reduce it to 7" at the thimble. Flue temps rise at least 50ºF at the reduction because of this restriction. What happens on the other side when the gases slow down and expand inside the extra volume of the square flue? I looked through the FAQ and couldn't seem to find an answer to these questions.

kwikrp said:

I have an old VC defiant early 80's. I am using well seasoned hardwoods as well as bio bricks and a few pieces from pallets. This is what happens from a cold start takes several hours to get to 400*. I basically keep throwing in wood and burning with the primary and secondary wide open and even the door a crack open. If not the fire will smolder and temps will be around 200*. To me it seems like there is a air supply restriction. I took it apart last year resealed it and cleaned out the back of the fire box. I can take a flashlight and shine it through the primary and secondary and I can see light entering the fire box! I have a 25 ft masonry interior chimney with 8 x 8 clay flue. It was cleaned in Sept of '09. Have check no blockages or obstructions.Well once I can get stove over 500* it is great heats well. But the battle is exhausting to get the stove top to that point.
Is it possible that the chimney is taking so long to heat to create a strong draft? I have observed that sometimes with the doors a crack open that the doors begin to be sucked in a bit. I also have taken a lit cigar (cohiba) and have opened the doors to the stove and have help the cigar up to 8 inch away and the smoke goes horizontal and up the stack. Maybe to much draft I dont know. Any help or thoughts would greatly be appreciated.
I have also observed that on occasion when I open the air supplies one would think that I would be heading towards an over-fire, but just the opposite happens the temp begins to drop.

Click to expand...

i to run a defiant from 1978. my setup is stove out at top up 18 inches 90 over 3 feet then thimble into the chimney from that point to the top of my chimney, 10 feet. from that point down to the cleanout 10 feet. that is not much of a chimney. this stove comes up to 600 degrees with sizzling wood starting from cold in between 30 and 60 minutes. you said above, that you can see light in the firebox shining a light into the secondary air opening. if you shine a light into the secondary air hole you should not see light in the firebox. now because of what you said i'll ask this. when you rebuilt the stove did you put cement on both sides of the air passage for the secondary air? meaning cement on the stove back and fireback upper groove and lower groove? if i run wood the is not dry in my stove with both primary and secondary air open it will over fire the stove. just the other day when getting it up to temp i forgot about the secondary air being open and the stove was running at 800 - 850 degrees. put your flashlight in the secondary burn chamber and you should only see light at the air hole inlet. if you forgot to, or the cement didn't stick to the grooves the the air coming in to either the primary or secondary some of that air can leak by the damper and go out the chimney. making it seem like you have a even shorter chimney.
question: where do you put your thermometer?
question: do you have single wall pipe or double wall?
if you close your side door to just where the latch prevents you from closing the door that should get you so much air on the fire to in time melt that stove down. where i have trouble is where the stove connector pipe goes into the thimble. the cement seems to draw alot of heat out and that's where i can get buildup.

Battenkiller said:

As for my installation... Guilty, guilty and guilty.


I have a 4' sump that goes down to the cleanout door. I've often wondered about its effect on my draft. Can that be temporarily sealed off somehow? How do you seal the cleanout door better? It seems rather flimsy to use gasketing material. Do these two thing make a significant difference?

On flue size, the original VC literature recommends an interior masonry chimney as the ideal chimney, and specifies a 8x8" nominal size liner. My 8x8" liner has a measured 7x7" inside diameter. That is 49 sq.in. compared to 50 sq.in. for 8" round pipe... a negligible difference IMHO. However, I was told that since smoke spirals as it rises, my 8x8" (7x7" ID) square clay-tile flue only has the flow characteristics of 6" round pipe? I've never been able to find a table for that. What is your opinion?

Also, in order to gain access to the inside of a 8x8" flue, you need to have a 8" round thimble. But a 8" nominal size thimble has a 7" ID. This creates a flow restriction at the thimble. I run 8" pipe straight up to a single 8" elbow and reduce it to 7" at the thimble. Flue temps rise at least 50ºF at the reduction because of this restriction. What happens on the other side when the gases slow down and expand inside the extra volume of the square flue? I looked through the FAQ and couldn't seem to find an answer to these questions.

Click to expand...

The little things add up to make a big difference!
Seal all the pipe joints!
Take a wad of fiberglass insulation and stuff it up the cleanout a few feet....that will seal off a lot of the sump.
The pipe reduction is probably closer to a 7"....yes, smoke uses mostly the round part. You can probably overcome that if everything else is good.