Lopi Leyden advice

[webby3650]

No, I've never done it that way. I vacuum through the holes in the combustion brick to get to the combustor. Then I remove the top flue and vacuum from the top to get around the sides. Both just like it says in the owner's manual. Seems easier than removing the refractory bricks. I like to leave all refractory parts in place so that a coating of insulating ash helps seal the seams. Anyway, my vacuuming method seems to work in that when we're done, there's a lot of ash in the vacuum bag.

But I will say that this vacuuming the brick doesn't seem to make any difference in how it operates. Not like vacuuming the ash pan and ash drawer gaskets surfaces so that the ash drawer has room for the door to fit and the gasket surfaces are air tite.
Like any stove with an ash collection area beneath the fire, it's critical that the ash drawer be air tight.

What about the Isle Royale? I'm curious about that stove. How does it's operation differ?
tnx, rScotty

It requires no baby sitting. Just loves to burn!
I don't mean to beat up on ya about the Leyden. I've had a dozen stoves or so, and work on most every stove on the market. Rear combustion stoves are by far my least favorite. Ive lost almost all faith in Lopi over the Leyden and then the cape cod. I've only had the quad for a few months, so far it's impressive. I assure you I'll be sure to post up my results!

 

[rScotty]

It requires no baby sitting. Just loves to burn!
I don't mean to beat up on ya about the Leyden. I've had a dozen stoves or so, and work on most every stove on the market. Rear combustion stoves are by far my least favorite. Ive lost almost all faith in Lopi over the Leyden and then the cape cod. I've only had the quad for a few months, so far it's impressive. I assure you I'll be sure to post up my results!

Shucks webby, it doesn't bother me to beat up on the Leyden. After all, how else will we improve it? I'm right with you. Please know that I don't have any personal stake here. I only own the stove; I had nothing to do with the design or the manufacture.
My suggestion is that we just try to figure out what it is capable of doing, where the problems are, and then work to make it better for what it is.

It seems to me that everyone who take the time to relate to a wood stove in the first place is probably a bit of a handyman and a problem solver. That makes wood stove people my kind of folks.

The Leyden obviously needs help with the sealing and the primary air flow - but that's fairly obvious to any owner after running it for a season. By the second season I had also proven to my satisfaction that it would not burn consistently in the fully damped position. It would either run way too hot or more likely would keep going out. So for the past few seasons we have run it with the damper locked at about 10% open. That's a shame, but no way to fix that that I'm aware of with this stove.

And like you say, I don't like secondary combustion taking place low down in the rear in any stove. Nor do I like the hot secondary combustion taking place right at the flue outlet like it does on so many of today's catalytics. I'd prefer secondary combustion to take place as a stratified layer within the upper part of the primary combustion box. That way I can keep an eye on it happening, too. With a bit of care and at 90% damped it's possible to get the Leyden to burn that way for awhile. Sometimes for several hours. But it's touchy.

The Leyden has it's good points. Nice aesthetics. And it does seem to be made of high quality cast iron nice thick extra metal in the stress areas and on gasketing surfaces. Good enamaling. I'm actually surprised at how strong and well cast that it is. So overall, it does seems to be well made. But maybe this one is the exception. What have you heard of the Leyden's structural strength? What about Cracking? Warping? Burn through?
In all those respects the Leyden seem better than many of those old made in USA cast iron stoves from previous generations.
Lets keep after it,
rScotty

 

[webby3650]

Shucks webby, it doesn't bother me to beat up on the Leyden. After all, how else will we improve it? I'm right with you. Please know that I don't have any personal stake here. I only own the stove; I had nothing to do with the design or the manufacture.
My suggestion is that we just try to figure out what it is capable of doing, where the problems are, and then work to make it better for what it is.

It seems to me that everyone who take the time to relate to a wood stove in the first place is probably a bit of a handyman and a problem solver. That makes wood stove people my kind of folks.

The Leyden obviously needs help with the sealing and the primary air flow - but that's fairly obvious to any owner after running it for a season. By the second season I had also proven to my satisfaction that it would not burn consistently in the fully damped position. It would either run way too hot or more likely would keep going out. So for the past few seasons we have run it with the damper locked at about 10% open. That's a shame, but no way to fix that that I'm aware of with this stove.

And like you say, I don't like secondary combustion taking place low down in the rear in any stove. Nor do I like the hot secondary combustion taking place right at the flue outlet like it does on so many of today's catalytics. I'd prefer secondary combustion to take place as a stratified layer within the upper part of the primary combustion box. That way I can keep an eye on it happening, too. With a bit of care and at 90% damped it's possible to get the Leyden to burn that way for awhile. Sometimes for several hours. But it's touchy.

The Leyden has it's good points. Nice aesthetics. And it does seem to be made of high quality cast iron nice thick extra metal in the stress areas and on gasketing surfaces. Good enamaling. I'm actually surprised at how strong and well cast that it is. So overall, it does seems to be well made. But maybe this one is the exception. What have you heard of the Leyden's structural strength? What about Cracking? Warping? Burn through?
In all those respects the Leyden seem better than many of those old made in USA cast iron stoves from previous generations.
Lets keep after it,
rScotty

I've seen warped tops, cracked platforms, warped top loading lids, failed combustion boxes, failed refractory, unexplainable backpuffing, run away fires. I'm sure there something I'm forgetting. To be honest I can't think of any good old iron stoves made in the USA. VC would be it, it was never good in my opinion...

 

[branchburner]

What about the Isle Royale? I'm curious about that stove. How does it's operation differ?

The secondary combustion takes place in the firebox (with burn tube technology) rather than in a separate rear combustion chamber (downdraft technology).

 

[rScotty]

I've seen warped tops, cracked platforms, warped top loading lids, failed combustion boxes, failed refractory, unexplainable backpuffing, run away fires. I'm sure there something I'm forgetting. To be honest I can't think of any good old iron stoves made in the USA. VC would be it, it was never good in my opinion...

That's my feeling too. The VC would be it, but I'm not a fan of cast iron stoves - having owned quite a few of them. Just off the top of my head: 2 Jotuls, 2 Vermont Castings, Live Oak, Majestic, Home Comfort, Lopi Leyden.
My dream stove might well have a cast iron outer with an enamel coat - but only if that cast iron outer skin surrounded a completely welded steel inner firebox.
The VC always interests me. Vermont Castins have a simple effective thermostat that can be used either to control the burn or as a hi heat safety switch. I like that it works by restricting intake air & not damping. VCs are top loading too.
The older I get, the more I value top loading....
In fact, the only thing I don't like about the VC is the cast construction.
rScotty

 

[Woody Stover]

My dream stove might well have a cast iron outer with an enamel coat - but only if that cast iron outer skin surrounded a completely welded steel inner firebox...The older I get, the more I value top loading.

Sounds like a PE Alderlea...and a Jotul Rangeley has top loading.

 

[webby3650]

Sounds like a PE Alderlea...and a Jotul Rangeley has top loading.

Blaze King Ashford too.

The top loading feature of the rangeley is nearly useless, with the door open you only have access to a very small part of the firebox. To fill it up you'd need to open both top doors, yes, inner and outer loading doors, drop in a few pieces of wood, then open the front door to push the wood back so you can add more wood. The quad is much better but still has very limited access to the deep firebox. It's good for dropping in a piece or two throughout the day. For overnight burns you have to load from the front.

 

[webby3650]

That's my feeling too. The VC would be it, but I'm not a fan of cast iron stoves - having owned quite a few of them. Just off the top of my head: 2 Jotuls, 2 Vermont Castings, Live Oak, Majestic, Home Comfort, Lopi Leyden.
My dream stove might well have a cast iron outer with an enamel coat - but only if that cast iron outer skin surrounded a completely welded steel inner firebox.
The VC always interests me. Vermont Castins have a simple effective thermostat that can be used either to control the burn or as a hi heat safety switch. I like that it works by restricting intake air & not damping. VCs are top loading too.
The older I get, the more I value top loading....
In fact, the only thing I don't like about the VC is the cast construction.
rScotty

The Blaze King Ashford has a welded firebox, cast iron jacket and a thermostatic air control. Other than the top load, this sounds like your next stove!

 

[Woody Stover]

The top loading feature of the rangeley is nearly useless, with the door open you only have access to a very small part of the firebox

Yeah, I watched a youtube and it looked like a small opening. Not sure I'd want that pivoting baffle either. Just seems like more moving parts.

The Blaze King Ashford has a welded firebox, cast iron jacket and a thermostatic air control. Other than the top load, this sounds like your next stove!

Not sure if rScotty is a cat guy or not...

 

[rScotty]

Yeah, I watched a youtube and it looked like a small opening. Not sure I'd want that pivoting baffle either. Just seems like more moving parts.
Not sure if rScotty is a cat guy or not...

To tell the truth, I'm not sure if I'm a cat guy or not myself. (with apologies to my little buddy currently sleeping on the couch)
I like the idea of reducing emissions - although from a larger perspective 'm not sure that it much matters if a tree decays in the woods or burns in my wood stove. Maybe it makes a difference in a populated area; that's not the case here.

What I don't like about catalytics is that the stove has to burn so dangerously hot to fire it off. And then once the cat begins to operate, even more heat is created. Frankly, I don't like to run my stove that hot in the first place. Besides, the stove might be efficient at that temperature, but my house isn't.

What I want to buy next time is a stove that runs dependably when turned way down. Who decided to rate stoves at full throttle anyway? That seems crazy to me. I never turn a wood stove up except for the initial start or more likely to get the coals glowing in the morning, and I never, ever leave it unattended until it is turned back down.

For my situation I don't see any advantage to having a high temperature catalyst. I wish there was an advantage I could use. A low temperature catalyst would sure be a selling point though. I'd be willing to pay well for that.
rScotty

 

[rScotty]

The Blaze King Ashford has a welded firebox, cast iron jacket and a thermostatic air control. Other than the top load, this sounds like your next stove!

How does that Blaze King thermostatic air control operate? How does the ACC operate?
I see them both advertised, but don't quite understand the way they work. By contrast, the VC thermostat is simple enough that I can easily understand it.
rScotty

 

[Woody Stover]

not sure that it much matters if a tree decays in the woods or burns in my wood stove.

Yes, the amount of carbon released is the same, but the cat will burn more of the particulates generated from burning.

What I don't like about catalytics is that the stove has to burn so dangerously hot to fire it off. And then once the cat begins to operate, even more heat is created. Frankly, I don't like to run my stove that hot in the first place. What I want to buy next time is a stove that runs dependably when turned way down. Besides, the stove might be efficient at that temperature, but my house isn't.

I don't burn my stove very hot at all to ramp up to cat operating temp. I post all the time that I favor a moderate ramp-up. No sense in stressing the stove with excess heat. Sure, I have somewhat lively flames for twenty or thirty minutes, but by no means is this anything close to a roaring fire. Once the stove is up to temp, I close the bypass and cut the air to maybe .3-.5 on a scale of 4. With no flame in the box and the cat eating the smoke, the hottest spot on the stove will then be over the cat, with my stove top meter there reading about 500*. The cat might be over 1000 but there is a heat shield above it, protecting the top of the stove. The sides of the stove will be at 350 or less when in a low cat burn. In fact, one advantage of a cat stove is the fact that it can run at a lower heat output, and still burn clean, than can a non-cat. The cat will burn smoke at 500*, a tube stove must have 1100* for the re-burnto happen. I seldom run my stove at high output, most often it's just idling along. It seems if I open up the air very much, to where I have flame in the box, some of the smoke starts getting past the cat un-burned. So I normally run with the air down to where there is no smoke coming out the stack. That's enough to keep the room temp here at 70.
If you do decide to get a new stove, don't make a snap decision based on a couple of posts by new owners of any particular stove, raving about how great it is. Rather, read threads on various stoves in depth to get a feel for how they're going to perform over the long haul, and any problems you might expect to encounter from them.

 

[Woody Stover]

BK thermostat is like the old VC, a spring. Not sure about ACC or Pacific Energy's EBT2. Lotta threads to be read to get an idea of what's really happening with these systems.

 

[branchburner]

What I don't like about catalytics is that the stove has to burn so dangerously hot to fire it off. And then once the cat begins to operate, even more heat is created. Frankly, I don't like to run my stove that hot in the first place. Besides, the stove might be efficient at that temperature, but my house isn't.

What I want to buy next time is a stove that runs dependably when turned way down.

It sounds like what you might want actually IS a cat. I have no experience with them other than the newer cat-hybrids from Woodstock, but what you are describing is totally at odds with what I have seen. Using good dry wood, the stove comes up to a moderate temp that allows me to engage the cat and run the stove while maintaining both flue temps and stove-top temps that can be considerably lower than with my Oakwood.

I am curious if you monitor your flue temps with the Leyden. My experience with the Oakwood is that they ran much higher (when the rear afterburner was cruising along) than with stoves having either burn-tube or cat-hybrid technology. My impression is that a cat can give the lowest operating flue temps without producing creosote, meaning the least amount of heat lost up the flue.

I suppose there are example of cat stoves "running away" or overfiring, but that scenario seems more likely with a stove like the Leyden. For good stoves that can be run efficiently at low burns with lower flue temps, consider the cats from BK and the cat-hybrids from Woodstock.

 

[Woody Stover]

I am curious if you monitor your flue temps with the Leyden. My experience with the Oakwood is that they ran much higher (when the rear afterburner was cruising along) than with stoves having either burn-tube or cat-hybrid technology. My impression is that a cat can give the lowest operating flue temps without producing creosote, meaning the least amount of heat lost up the flue.

I was going to mention temp meters but forgot to address this in my post. I have one meter lying on top of the tee snout about 6" behind the flue collar, which should be the hottest place to monitor flue temps. I don't let that meter get above 600. The cat meter is a probe that enters the back of the stove in the area of the flue exit. Before the cat is engaged, that meter tells me the internal temp of the stove around the flue exit. I cut air during the ramp-up to level off the probe around 900-1000, then let the meter on the stove top above the cat reach about 200 or so, then close the bypass, and the cat lights off.

I suppose there are example of cat stoves "running away" or overfiring, but that scenario seems more likely with a stove like the Leyden. For good stoves that can be run efficiently at low burns with lower flue temps, consider the cats from BK and the cat-hybrids from Woodstock.

Once I have the bypass closed and cat lit, I cut the air down to the setting I want for the bulk of the burn cycle. Stove temps maintain that level, then slowly drop as the load gasses out and eventually becomes coals. I never have to worry that the stove temp is going to rise or that the stove will run away.

 

[rScotty]

It sounds like what you might want actually IS a cat. I have no experience with them other than the newer cat-hybrids from Woodstock, but what you are describing is totally at odds with what I have seen. Using good dry wood, the stove comes up to a moderate temp that allows me to engage the cat and run the stove while maintaining both flue temps and stove-top temps that can be considerably lower than with my Oakwood.

I am curious if you monitor your flue temps with the Leyden. My experience with the Oakwood is that they ran much higher (when the rear afterburner was cruising along) than with stoves having either burn-tube or cat-hybrid technology. My impression is that a cat can give the lowest operating flue temps without producing creosote, meaning the least amount of heat lost up the flue.

I suppose there are example of cat stoves "running away" or overfiring, but that scenario seems more likely with a stove like the Leyden. For good stoves that can be run efficiently at low burns with lower flue temps, consider the cats from BK and the cat-hybrids from Woodstock.

Why would runaway be more likely on the Leyden?

Sounds to me like I need to do some more research and figuring about cats. And it sounds like both you and Woody have differnent experiences from the things that I've heard. I've never actually used a cat. They aren't popular out west. Don't know why. My buddy doesn't like his ( on a VC) - too hot, but yours sounds like it works differently. Are you talking about Woodstocks? I've never seen one.

On the Leyden we get secondary burn but it happens in the firebox with the damper bypass partly open. Completely closing the bypass doesn't seem to be a reliable option on this stove.

I do monitor temperatures but only with a bi-metallic temp gauge and not constantly. That needs improvement. Especially as I work with the Leyden.... What I'd like is to monitor half a dozen points constantly via thermocouples on the stove, flue, and pipe. I'm concerned about the temp on the pipe because it goes through a chaise in the attic. Definitely a need to put in some kind of remote monitoring setup. Ideas?
thanks,
rScotty

 

[begreen]

To be honest I can't think of any good old iron stoves made in the USA. VC would be it, it was never good in my opinion...

If we are talking good old cast iron stoves, the original VC line was excellent, IMO. The castings were beautiful and durable and the stoves did what they were designed to do pretty well for late 70's tech. Many are still in service today. It wasn't until the Acclaim and the introduction of refractory packages as a solution to meet EPA phase 2 that the line went downhill.

The Regency Hampton line isn't ok, but that is Canadian. Not sure where they are cast.

 

[branchburner]

Why would runaway be more likely on the Leyden?

On the Leyden we get secondary burn but it happens in the firebox with the damper bypass partly open. Completely closing the bypass doesn't seem to be a reliable option on this stove.

I'm not sure about the newer configuration of the Leyden, where the damper bypass can be partly open, but with my Oakwood and other downdrafts I know, closing the bypass forces all the flue gasses into the rear combustion chamber, where most secondary combustion takes place. The only time I could see an adjustable damper would be in bringing the stove up to temp, before closing it completely to get secondaries.

That chamber has to be very hot to initiate secondaries, and once they get going with a full load of nice, dry wood the stove really cranks, sometimes creating a slight and audible "rumble" where you can hear the intensity of the combustion. In cases where there is extremely strong draft (or overdraft) it was not unheard of for this secondary combustion to "run away" to some degree, pushing surface temps over an 800f "overfire" range and even high enough to make the stove faintly glow. It also seems typical for external single-wall flue temps to run 50-100f higher with these stoves, at least with MINE, than with other burn technologies.

I understand there have been many revisions to the Leyden, but I am curious about leaving the bypass partly open and achieving secondaries in the main firebox. Is this method in a revised manual or brochure, and are there any burn tubes or other aids to secondary combustion contained within the main firebox? Again, I can't speak to the particulars of your stove. Here is old thread typical of problems sometimes reported:
https://www.hearth.com/talk/threads/lopi-leyden-red-hot.48953/

 

[webby3650]

I'm not sure about the newer configuration of the Leyden, where the damper bypass can be partly open, but with my Oakwood and other downdrafts I know, closing the bypass forces all the flue gasses into the rear combustion chamber, where most secondary combustion takes place. The only time I could see an adjustable damper would be in bringing the stove up to temp, before closing it completely to get secondaries.

That chamber has to be very hot to initiate secondaries, and once they get going with a full load of nice, dry wood the stove really cranks, sometimes creating a slight and audible "rumble" where you can hear the intensity of the combustion. In cases where there is extremely strong draft (or overdraft) it was not unheard of for this secondary combustion to "run away" to some degree, pushing surface temps over an 800f "overfire" range and even high enough to make the stove faintly glow. It also seems typical for external single-wall flue temps to run 50-100f higher with these stoves, at least with MINE, than with other burn technologies.

I understand there have been many revisions to the Leyden, but I am curious about leaving the bypass partly open and achieving secondaries in the main firebox. Is this method in a revised manual or brochure, and are there any burn tubes or other aids to secondary combustion contained within the main firebox? Again, I can't speak to the particulars of your stove. Here is old thread typical of problems sometimes reported:
https://www.hearth.com/talk/threads/lopi-leyden-red-hot.48953/

Never was the bypass designed to be partially open on the Leyden. Opened or closed like other stoves.

 

[webby3650]

Why would runaway be more likely on the Leyden?

Sounds to me like I need to do some more research and figuring about cats. And it sounds like both you and Woody have differnent experiences from the things that I've heard. I've never actually used a cat. They aren't popular out west. Don't know why. My buddy doesn't like his ( on a VC) - too hot, but yours sounds like it works differently. Are you talking about Woodstocks? I've never seen one.

On the Leyden we get secondary burn but it happens in the firebox with the damper bypass partly open. Completely closing the bypass doesn't seem to be a reliable option on this stove.

I do monitor temperatures but only with a bi-metallic temp gauge and not constantly. That needs improvement. Especially as I work with the Leyden.... What I'd like is to monitor half a dozen points constantly via thermocouples on the stove, flue, and pipe. I'm concerned about the temp on the pipe because it goes through a chaise in the attic. Definitely a need to put in some kind of remote monitoring setup. Ideas?
thanks,
rScotty

The Leyden is NOT catalytic. It's secondary combustion takes place in the rear of the stove but does not utilize a catalytic combuster. It takes extreme conditions to produce secondary combustion, whereas cat stoves only need a small amount of heat in comparison to creat a clean burning environment. All cat stoves are not created equal, VC should not be the control for cat stoves! They are very poor performers in comparison to the other cat stoves still produced! I.E. BK and Woodstock.

 

[branchburner]

Never was the bypass designed to be partially open on the Leyden. Opened or closed like other stoves.

Well, that would be my assumption, until rScotty posted this earlier in the thread:
"... a kit showed up from the factory which contained parts to fix the problem that I hadn't even told them about. The fix was simple, clever, and easy to install. 100% fix, and also allowed the bypass to be set (and to stay set) in an infinite range of positions. "

That is the ratcheting modification, correct? Why ratchet if not intended to be in multiple positions?

And then he writes:
"On the Leyden we get secondary burn but it happens in the firebox with the damper bypass partly open. Completely closing the bypass doesn't seem to be a reliable option on this stove."

 

[bholler]

In fact, the only thing I don't like about the VC is the cast construction.

There is a whole lot more to dislike about vc stoves than that.

 

[rScotty]

Well, that would be my assumption, until rScotty posted this earlier in the thread:
"... a kit showed up from the factory which contained parts to fix the problem that I hadn't even told them about. The fix was simple, clever, and easy to install. 100% fix, and also allowed the bypass to be set (and to stay set) in an infinite range of positions. "

That is the ratcheting modification, correct? Why ratchet if not intended to be in multiple positions?

And then he writes:
"On the Leyden we get secondary burn but it happens in the firebox with the damper bypass partly open. Completely closing the bypass doesn't seem to be a reliable option on this stove."

Thank you, branchburner. Yes, I was referring to the ratcheting modification that Lopi provided as an improvement to the bypass lever operation. A simple latch would have been easier to design. Looking at the kit, my assumption was that this was a factory modification to allow the degree of bypass to be adjusted by the user - since doing so was clearly necessary in order to get the stove to run correctly. I set mine to allow for for six different bypass positions including full open or fully shut.
I'm sure I'm not the only person who found that reliable burning required the bypass to be only partly closed. As a bonus, we can sometimes get a secondary burn going right at the top of the firebox. Unusual & beautiful bright whispy dancing flames. It would appear that a reliable secondary burn on this stove requires being able to visually see the secondary flames. Is that true of all stoves? I suspect it is... BTW, I usually run mine at about 60% closed. That is a position that works well for my stove and I have marked the ratcheting bypass lever so that it is repeatable.

No, the original owner's manual does not mention running with the bypass lever partly engaged. But keep in mind that manual was written before the company made the modification to the lever that allows for positive locking at partial engagement.

Frankly I didn't find the owner's manuals to be correct as to the stove operation. That didn't surprise me, and that was good since this one has a number of questionable passages. On page 21 regarding bypass lever operation, the bypass lever is described as being "pulled out or pushed in". That's clearly incorrect. The bypass lever is rotated; not pushed at all. It is the air intake that works by being pulled out or pushed in.
On the next page of the manual it recommends that after starting the stove it be run with the bypass wide open and the air flow at maximum for up to 45 minutes in order to get the stove up to heat before engaging the bypass.....
Still learning,
rScotty

 

[branchburner]

It would appear that a reliable secondary burn on this stove requires being able to visually see the secondary flames. Is that true of all stoves?

In fact, both downdraft (Leyden/Oakwood) and cat technologies allow for secondary burning to occur out of sight, so a firebox that may appear to be "smoldering" or out altogether might have good secondary combustion occurring "behind the scenes." Wispy ghost flames would occur in my Oakwood's firebox, but since the rear combustion chamber is out of sight, the only way to confirm it was fully engaged was to check the external temps (starting to glow is a pretty good indication that secondaries are raging).

In burn tube stoves (or hybrid-cats w/ burn tubes) the secondaries are in full view, in the main firebox rather than in a catalyst chamber or rear combustion package.

 

[rScotty]

In fact, both downdraft (Leyden/Oakwood) and cat technologies allow for secondary burning to occur out of sight, so a firebox that may appear to be "smoldering" or out altogether might have good secondary combustion occurring "behind the scenes." Wispy ghost flames would occur in my Oakwood's firebox, but since the rear combustion chamber is out of sight, the only way to confirm it was fully engaged was to check the external temps (starting to glow is a pretty good indication that secondaries are raging).

In burn tube stoves (or hybrid-cats w/ burn tubes) the secondaries are in full view, in the main firebox rather than in a catalyst chamber or rear combustion package.

I believe that the Isle Royale is a burn tube design. If so, it's the only one I know of. Who makes a hybrid-cat w/ burn tubes that features a full view of the secondary combustion?
I like being able to view the fire, and think of it as being a fairly recent technological advance in wood stoves. No wood stove used to offer that feature; now most of them do. It's a great upgrade in aesthetics as well as giving us more knowledge about the burn.
rScotty