Newbie questions

[Black Jaque Janaviac]

I've been buring wood for a few years so I'm not entirely new to woodburning. However we recently moved into a house with hot water baseboard heat.

I just put an insert in the living room fireplace and it does a so-so job. However, I prefer the heat distribution of the baseboard. The way the baseboards are plumbed, zoning them is impossible. One thermostat runs the boiler and to change that would be a major overhaul.

I'm curious about these indoor wood boilers.

1) Do I understand correctly that they use the thermal mass of the firebrick to maintain temperatur in the firebox above ignition temp for several hours? Thus, when the thermostat shuts off, all combustion is stopped, then when the thermostatic kicks in all that is needed is a shot of fresh air and it starts up again?

2) Does this ability to cease combustion translate into a big savings on wood consumption?

I have room for one more insert in the basement. I figure that with two inserts burning on the coldest winter days the entire house should be comfortable. But if these boilers are truly more efficient than an EPA certified insert, I might save my pennies for a boiler instead. Using less fuel has it's own positives. More space in my yard. Less worry about where, how and when to aquire wood.

 

[ISeeDeadBTUs]

It would be cool if it were actually possible to stop wood cumbustion . . .then restart it on demand. Many manufacturers claim this. I bought a GreenWood, which claimed they could do it. They can't. Many Euro units (including Viessmann) claim they can halt cumbustion. I believe the WoodGun makes this claim too. All good units. I doubt any of them can actually do what you think they can.

 

[Black Jaque Janaviac]

It would be cool if it were actually possible to stop wood cumbustion . . .then restart it on demand. Many manufacturers claim this. I bought a GreenWood, which claimed they could do it. They can’t. Many Euro units (including Viessmann) claim they can halt cumbustion. I believe the WoodGun makes this claim too. All good units. I doubt any of them can actually do what you think they can.

OK, so manufacturers are overstating their product abilities. That's nothing new.

I take it this means that they don't entire stop combustion, but let it "smolder". How is this any different than the Outdoor Wood Boilers I see fogging up the countryside?

If these are nothing more than an OWB put indoors I'm not interested. The extra hassle of using fireplace inserts is worth maintaining good relationships with the neighborhood.

 

[Como]

The Wood Gun is the only one I have seen that implies no storage. And I do not understand it either. All the Euro log units I have seen specify storage.

If you went with pellets/chips then you can modulate much more easily.

Gassifiers and OWB's are completely different products.

 

[Singed Eyebrows]

Black Jaque; The WG does not smolder on idle. The intake shuts off airtite with a silcone rubber gasketed motorized flap. The chimney then pulls a slight vacuum on the boiler. What this does exactly is something for a combustion engineer to determine. WG uses the term "dormant" & when fresh air is added quite a bit later the wood starts up again. Muncie Bob is sorting out his newly installed WG & he should be able to further comment on this. From what I have gathered this works well, you can't let it on idle for real long periods though or you will lose the fire, Randy

 

[mike1234]

Just from the description of it, dormant = smoldering, or maybe controlled smoldering.

Black Jaque; The WG does not smolder on idle. The intake shuts off airtite with a silcone rubber gasketed motorized flap. The chimney then pulls a slight vacuum on the boiler. What this does exactly is something for a combustion engineer to determine. WG uses the term "dormant" & when fresh air is added quite a bit later the wood starts up again. Muncie Bob is sorting out his newly installed WG & he should be able to further comment on this. From what I have gathered this works well, you can't let it on idle for real long periods though or you will lose the fire, Randy

 

[Singed Eyebrows]

Just from the description of it, dormant = smoldering, or maybe controlled smoldering.

Black Jaque; The WG does not smolder on idle. The intake shuts off airtite with a silcone rubber gasketed motorized flap. The chimney then pulls a slight vacuum on the boiler. What this does exactly is something for a combustion engineer to determine. WG uses the term "dormant" & when fresh air is added quite a bit later the wood starts up again. Muncie Bob is sorting out his newly installed WG & he should be able to further comment on this. From what I have gathered this works well, you can't let it on idle for real long periods though or you will lose the fire, Randy

Smoldering to me means that the wood is getting limited oxygen. The WG intake shuts off airtite. I don't believe a wood fire smolders with no oxygen or that combustion can even occure. I don't believe "dormant" as WG uses the term & smoldering are the same, Randy

 

[Medman]

Reignition will occur if the temp in the firebox is kept above the level needed for spontaneous combustion of the fuel. As long as the wood/coals are hot enough, the fire will restart as soon as oxygen is introduced. If the firebox is closed airtight, there will be no smoke or smouldering.
EKO does not do this - the firebox is not airtight during idle, thus there is some smouldering - not enough to see at the stack, but it will eventually use up the fuel in the firebox. That is why storage is recommended, so that this loss of BTU's does not occur.

 

[Black Jaque Janaviac]

Thanks guys.

Again - I'm ignorant of the boiler lingo. By storage, do you mean a several hundred gallon tank to hold hot water?

The wood gun sounds like it's the only one that attempts to completely shut off. When you say you can't let it idle for long periods how long is long? 1 hour? 8 hours? A day? I imagine that in the fall and spring the gas boiler could do the work when heat demand will be spaced far apart. But if the Wood Gun can hold ignition temperature for a couple hours, I'd imagine we could keep it going from December to March without lighting more than one match.

Even if the air intake completely seals, the high temps will continue to gasify the wood. If this gas has no place to go, the pressures will rise. So I imagine that even with the intake completely sealed airtight there will be some discharge.

Perhaps, in the interest of air quality this excess wood-gas gets combusted through a secondary burn, even though the primary burn air supply is completely zero?

 

[Singed Eyebrows]

Thanks guys.

Again - I'm ignorant of the boiler lingo. By storage, do you mean a several hundred gallon tank to hold hot water?

The wood gun sounds like it's the only one that attempts to completely shut off. When you say you can't let it idle for long periods how long is long? 1 hour? 8 hours? A day? I imagine that in the fall and spring the gas boiler could do the work when heat demand will be spaced far apart. But if the Wood Gun can hold ignition temperature for a couple hours, I'd imagine we could keep it going from December to March without lighting more than one match.

Even if the air intake completely seals, the high temps will continue to gasify the wood. If this gas has no place to go, the pressures will rise. So I imagine that even with the intake completely sealed airtight there will be some discharge.

Perhaps, in the interest of air quality this excess wood-gas gets combusted through a secondary burn, even though the primary burn air supply is completely zero?

Yes, storage is a large tank either pressurized or non pressurized. I can't answer the how long can it idle question, I've heard 4 hours & sometimes 8 hours, there are some variables though. The nozzles are not sealed on idle & they can vent to the chimney if the boiler pressurizes. To the best of my knowlege you will not get a secondary burn on idle with the WG although if the smoke is either drawn or forced through hot coals without the fan running you still should not get much polution, Randy

 

[muncybob]

I have limited experience with my WG(since Oct) but this is what I have observed: To the contrary, I do not believe the temperature of the "firebrick" is what reignites the fuel...rather, it is the bed of coals that reignite once air supply is reintroduced by the motorized flap on the fresh air intake tube and the draft fan is running(this always happens at the same time). That flap does indeed cut off any usable air to the coals so they will last a long time...how long would probably depend on the thickness of the bed but several hours is not unreasonable. I guess the small amount of air coming into the firebox via a natural draft is what keeps them alive. The condition under which the coals will die sooner would be if the water temp goes low enough to turn on the fan/air intake and there is no fuel to ignite...coals will burn rapidly. It's amazing to me though, how small a bed of coals you need to reignite! Many times I have laid large splits on top of a very small amount of coals and checked 10 minutes or so later and a good fire is going on. I'm sure the dryness of the splits plays a large part in that but isn't that true for any woodburner?

The unit that controls the air flap seals the air intake opening into the firebox with a fair amount of pressure so as long at the silicone "gasket" on that flap is smooth and the air intake opening is kept clean you can be fairly certain no air is entering there. Upon reaching temp to cut air intake I have noticed the water temp rise a just a few degrees and level off but it seems the pressure holds steady..... and later will slowly drop a bit with the water temp.

Hard for me to say if this saves on wood consumption at this stage since 1. I have no reference to compare it to(1st yr w/wood) and 2. only been burning a few months and late autumn was fairly warm. I can tell you that we keep our house at 70 until about 11pm when it drops down to 66 and back to 70 at 6am and we have burned about 1/2 cord to this point. Keeping coals going in the shoulder season was a challenge until I mastered the cycle timer.

Hope this helps....I'm still learning!

 

[ISeeDeadBTUs]

I just want someone to explain to me how you

1) make a combustion chamber 'airtight' when there is an opening called a chimney and
2)give us all an accurate scientific explanation of how a HOT piece of wood can ignite by blowing oxygen on it

That's all. 'Cause though the WG was on my short list, and I woulda bought a Viessmann if I'd known, they both claim this mysterious 'shut down' of the fire . . . and I think they're both full of sheetz

 

[Singed Eyebrows]

I just want someone to explain to me how you

1) make a combustion chamber 'airtight' when there is an opening called a chimney and
2)give us all an accurate scientific explanation of how a HOT piece of wood can ignite by blowing oxygen on it

That's all. 'Cause though the WG was on my short list, and I woulda bought a Viessmann if I'd known, they both claim this mysterious 'shut down' of the fire . . . and I think they're both full of sheetz

OK, let me try. The flap seals airtite & at this point the only way for air to enter the top chamber is through 2 small nozzles & these are at the bottom of the chamber. The chimney pulls a vacuum on the nozzles & air can't enter the chamber. Yes they are open as you are saying, under vacuum though. I don't think a hot piece of wood can ignite, as a previous poster(Medman) has said the wood must be above ignition temp for it to light, Randy

 

[muncybob]

Agreed!! The term airtight is not totally correct when referring to the burning chamber. But, with the amount of pressure on the air flap against the air intake opening and a clean flap seal...that should be airtight. The natural draft in the burning chamber is so little though that I think it is barely enough to keep any coals hot. I have peered into the air intake opening when the boiler is not firing and can barely make out that coals are present and I see no visual evidence of the remaining wood burning. I guess they are smoldering to some degree but I can't see any smoke.

It's not air onto a hot piece of wood that causes regnition...it's the reintroduction of air through the coals that gets the fire going again. No coals...no fire without manually starting one.

 

[mike1234]

The point being however, that the chimney opening never closes, and that is a source of O2 (maybe slight, but still a source), and if there is air, the fire is not dormant, thus smoldering. I'm not criticizing the boiler, I'm sure it works very well, 1/2 cord through this part of the years seems like great performance to me, I've burned a lot more than that. It's just that their claims of dormant and totally shutting off the oxygen seem not quite totally accurate.

I just want someone to explain to me how you

1) make a combustion chamber 'airtight' when there is an opening called a chimney and
2)give us all an accurate scientific explanation of how a HOT piece of wood can ignite by blowing oxygen on it

That's all. 'Cause though the WG was on my short list, and I woulda bought a Viessmann if I'd known, they both claim this mysterious 'shut down' of the fire . . . and I think they're both full of sheetz

OK, let me try. The flap seals airtite & at this point the only way for air to enter the top chamber is through 2 small nozzles & these are at the bottom of the chamber. The chimney pulls a vacuum on the nozzles & air can't enter the chamber. Yes they are open as you are saying, under vacuum though. I don't think a hot piece of wood can ignite, as a previous poster(Medman) has said the wood must be above ignition temp for it to light, Randy

 

[Singed Eyebrows]

The point being however, that the chimney opening never closes, and that is a source of O2 (maybe slight, but still a source), and if there is air, the fire is not dormant, thus smoldering. I'm not criticizing the boiler, I'm sure it works very well, 1/2 cord through this part of the years seems like great performance to me, I've burned a lot more than that. It's just that their claims of dormant and totally shutting off the oxygen seem not quite totally accurate.

I just want someone to explain to me how you

1) make a combustion chamber 'airtight' when there is an opening called a chimney and
2)give us all an accurate scientific explanation of how a HOT piece of wood can ignite by blowing oxygen on it

That's all. 'Cause though the WG was on my short list, and I woulda bought a Viessmann if I'd known, they both claim this mysterious 'shut down' of the fire . . . and I think they're both full of sheetz

OK, let me try. The flap seals airtite & at this point the only way for air to enter the top chamber is through 2 small nozzles & these are at the bottom of the chamber. The chimney pulls a vacuum on the nozzles & air can't enter the chamber. Yes they are open as you are saying, under vacuum though. I don't think a hot piece of wood can ignite, as a previous poster(Medman) has said the wood must be above ignition temp for it to light, Randy

I disagree, Once the flap closes airtite the oxygen is burned up in a short time. You are saying that then air can circulate through the nozzles into the top chamber. Air is not going to go back through this vacuum into the top chamber. I know from chemistry class that once a test tube has a vacuum pulled on it that it is open yet sealed from air. A carbon steel WG depends on this. Any air or smoldering & the plates will rot out because of no inlet temp protection. Leaky door seals etc is what did in Eschland, Randy

 

[ISeeDeadBTUs]

It's not air onto a hot piece of wood that causes regnition...it's the reintroduction of air through the coals that gets the fire going again. No coals...no fire without manually starting one.

Not trying to be argumentative here. . . . just tell me where I'm wrong please

If coals have no oxygen available, they become hot wood. Hot wood cannot spontaneously combust upon reintroduction of oxygen.

As others have said, this is not a knock on the WG or any other unit. But this whole air tight thing is impossible.

 

[Como]

They sought of acknowledge this with the carbon vs SS.

I do not knock the product. On my short list. But I also do not see how you can magically stop wood in mid combustion and then restart it again as is implied.

 

[muncybob]

It's not air onto a hot piece of wood that causes regnition...it's the reintroduction of air through the coals that gets the fire going again. No coals...no fire without manually starting one.

Not trying to be argumentative here. . . . just tell me where I'm wrong please

If coals have no oxygen available, they become hot wood. Hot wood cannot spontaneously combust upon reintroduction of oxygen.

As others have said, this is not a knock on the WG or any other unit. But this whole air tight thing is impossible.

I certainly will not be the one to tell you...my experiences are limted. But, I do feel you are getting too hung up on this "air tight" concept. I don't think I ever said anything about being "air tight" in the burn chamber. I do not feel the burn chamber is totally "air tight" when in "idle". I can only say from experience that my unit was in "idle" for several hours recently(I had it turned off to cool down & clean) and the amount of coals remaining near the nozzle was comparable to the amount of coals there when I shut it down....not exactly the same but very close.

But, isn't the question here how the WG can idle and reignite and not if it's "air tight"?

 

[Black Jaque Janaviac]

I just want someone to explain to me how you

1) make a combustion chamber ‘airtight’ when there is an opening called a chimney and
2)give us all an accurate scientific explanation of how a HOT piece of wood can ignite by blowing oxygen on it

You are correct, without blocking off the chimney, the combustions chamber is not air tight.

However, the concept of HOT wood, or charcoal, igniting upon introducing oxygen isn't out of the realm of possibility. When wood gets hot, it begins turning into vapor. That vapor is actually the part that combusts, provided it has sufficient oxygen and remains at a sufficient temperature.

Take a dry thin piece of wood and touch it to the electric element of your kitchen stove (fume hood on high). If you drop the wood chip in the middle of a large heating element it will smolder, then burst into flames. This is all done without a match or spark. You combined fuel and oxygen and then brought it up to the critical temperature where ignition occurs.

Now imagine your firebox got burning super hot, the firebrick reaches 1000*+ then the last of your wood get's burnt and there is nothing in the firebox. In fact you immediately sweep out the firebox. The brick is still holding at 1000*. There is plenty of oxygen in the box. Now throw in a thin wood chip. What do you think will happen? Same thing as on the stove right?

You might say, "wait a minute, when I load the stove up I don't see immediate ignition." That's because when you load the wood in you are putting large chunks of wood (thermal mass) that is way below 1000* or whatever. The wood either cools off the firebrick, or the wood cools itself off so that the outter layer of wood in contact with the brick is not sufficiently hot to ignite.

What these boilers are claiming to do is to remove one of the ingredients of combustion, oxygen, while maintaining the other two, temperature and fuel.

Here is where the manufacturer claims seem dubious to me. If that wood is surrounded by firebrick that is 1000*+ and it is completely starved of oxygen, that smoke has to go somewhere. If the chimney is sealed off, the combustion chamber will continue to build pressure, possibly dangerous levels. So they obviously don't block off the chimney. So that leaves the unburnt smoke to discharge out the chimney, not exactly EPA kosher.

 

[Black Jaque Janaviac]

Or better yet. Try this experiment.

Instead of laying the wood chip directly on the stove, put some woodchips in an amber glass cooking pot with a reasonably tight fitting lid. Put THAT on the kitchen range and crank the knob to high. Fume hood on please.

You should be able to see the wood chips turn black smoke, and maybe even glow for a while. Smoke, uncombusted wood gas, will begin billowing out from under the lid. After a while the chips should just turn black and the smoke should continue billowing out. This represents the moment when all the oxygen in the pot was consumed.

Let the wood chips get good and hot, then open the lid. The smoke should rise out, and the wood chips being exposed to oxygen, and remaining at the right temperature, should begin to glow.

Do the same thing with another pot, only this time turn the burner off and let the pot cool for several hours before opening the lid.

 

[ISeeDeadBTUs]

Ok, ok, ok . . . . this sheetz has gone too far when I gotta cook wood chips on Mrs J's stove :roll:

But anyway, yes, the issue of claiming airtight is a non-issue.

My GW can go into idle and 'restart' after a couple of hours. I try to avoid that, which is easy when it's this cold out and the wind is blowing. But what I'm saying is you cannot completely deprive the chamber of oxygen. Thus, almost imperceptably, the coals continue to burn. Burning in this oxygen deprived state is when creoste develops.During the summer I could build a small fire, let the GW get up to temp and go to idle. If the heat load never came on and the GW remained in idle. it would SLOWLY burn all the fuel up. It would take a long time, but it would still burn up.

I am having trouble believing that the WG, the Viessmann, or any other unit can do any better.

http://www.viessmann.com/com/en/products/Solid_fuel-fired_boilers/vitolig_200.html

I'm just sayin'

 

[Como]

Nice piece of kit, but I have a feeling it will be quite a few years before it gets to the US.

And being translated from the German may have resulted in some loss of inflection.

I checked the UK site, not available there.

 

[ISeeDeadBTUs]

It's available here :coolsmirk:

 

[Singed Eyebrows]

It's not air onto a hot piece of wood that causes regnition...it's the reintroduction of air through the coals that gets the fire going again. No coals...no fire without manually starting one.

Not trying to be argumentative here. . . . just tell me where I'm wrong please

If coals have no oxygen available, they become hot wood. Hot wood cannot spontaneously combust upon reintroduction of oxygen.

As others have said, this is not a knock on the WG or any other unit. But this whole air tight thing is impossible.

I certainly will not be the one to tell you...my experiences are limted. But, I do feel you are getting too hung up on this "air tight" concept. I don't think I ever said anything about being "air tight" in the burn chamber. I do not feel the burn chamber is totally "air tight" when in "idle". I can only say from experience that my unit was in "idle" for several hours recently(I had it turned off to cool down & clean) and the amount of coals remaining near the nozzle was comparable to the amount of coals there when I shut it down....not exactly the same but very close.

But, isn't the question here how the WG can idle and reignite and not if it's "air tight"?

Bob; The carbon steel WG must be airtite on idle or the plates will degrade from acid washing. There is no inlet mixer protection on the WG. The others do not accept that a vacuum seals off the chimney at the nozzles & that is fine. They need a mechanical flap etc & that isn't there. WG did a bunch of R&D to seal up the primary chamber because they learned from Eshlands mistakes. As I see it the only time an idling WG is not sealed is when the chimney has a down draft & goes to positive pressure. If you have a chimney that constantly pressurizes the WG you don't have a chimney, you have a pile of bricks, Randy