Down-Drafting Stove Design

[Rob From Wisconsin]

This seems to be one of the lastest rages in
stove combustion technology, where the
exhaust is pulled-down throught the coals,
thus resulting in cleaner, more even burns.
I know that Harman & V.C. make such stoves.
Does anyone have any experience with such a
unit?? Are the burns indeed longer & more "even"
(much like a catalytic stove)??

Thanks,
Rob

 

[Mike Wilson]

Quick question... which Harman or VC stoves do you know of that do this? I'd like to look at them.

Thanks...

-- Mike

 

[MountainStoveGuy]

wow, im in the loop, but not in this loop. News to me, i would love some links that explain this technology.

 

[Todd]

I think your talking about the Everburn system? I've heard of it but don't exactly know how it works. Something about a seperate combustion chamber in the back of the stove? Even Woodstock said their looking into this new technology or some kind of everburn catalyst thingy.

 

[berlin]

I wasn't aware that this was redily available from domestic stove manufacturors; although i haven't really been paying close attention either. This technology and variations of it have been around for many, many years, it is not new. In europe many residential and small commerical coal, wood, and peat fired boilers utilize this technology and its varieations. I am not convinced that outside of perhaps small emissions reductions there are any real worthwhile benefits.

 

[elkimmeg]

Quick question... which Harman or VC stoves do you know of that do this? I'd like to look at them.

Thanks...

-- Mike

The Everburn non-cat units in Dutchwest,
Encore and now Defiant are terrific stoves as well as the cleanest
burning non-cats made That's right a non cat Defiant new this year. I know it is being used in the Harman oakwood model
this technology works well with top loading stoves part of smoke leakage prevention


"The EVERBURN™ System after burner process: Gases produced from the burning of the wood are mixed with just the right amounts of air to ensure they are burned completely, producing clean emissions and efficient warmth. The state of the art ceramic fiber material used in an EVERBURN™ Non-Catalytic Combustion System"

 

[MountainStoveGuy]

sounds like typical secondary burn technology to me, the ceramic fiber part of this i assume is the baffle?

 

[Sandor]

This is what happens in the old VC Resolute Acclaim that my GF has. When in "secondary" burn mode, the top flue exit is closed and the flue gases exit at the very bottom of the firebox, then travel up behind the firebox in a "secondary" burn chamber.

Works rather well, actually, and makes a huge difference in burn time.

 

[webbie]

This seems to be one of the lastest rages in
stove combustion technology, where the
exhaust is pulled-down throught the coals,
Thanks,
Rob

This is another example of "technology regurgitation".....

This type of combustion goes by various names - base burning, downdraft, etc.

Riteway had a number of stoves in the late 70's that worked this way. You can find antique stoves at the Good Time Stove Co that are base burning designs...

BUT,

The most recent example was the VC Resolute Acclaim (non-cat), which was introduced in the late 1980's and used this technology. It worked well - too well, burned so hot that the whole stove virtually melted down after a few years and was in need of expensive parts replacement. Over the years they have beefed up the inside in an attempt to make it contain these high temps. If anyone here has used the newer models hard for over 5 years it would be good to hear a report.

In any case, it would be silly for folks to use woodstove marketing by manufacturers as the basis for buying new stoves. Yes, someone had to be the first to buy these new models, but as with many pioneers they may have a price to pay.

Just as with cars, a buyer has to determine what they want a stove for. If they want it to save money, they should look carefully into not only the initial price, but the service history and parts/repair costs. If they want it for some recreation or to show their friends, then these factors may not come into play.

 

[Corie]

I was under the impression, at least with the Harman that the secondary combustion has little to do with forcing the smoke back through the coal bed, but with mixing precise amount of air in. It just so happens that on these stoves, the combustion chamber is in the back and the smoke exits the lower rear of the firebox.

 

[elkimmeg]

3 years with my Resolute Acclaim, (11 cords of wood) running as I type. No melt downs yet, no sever overheating. The only reason I am replacing it is cat and 18% more heat capacity, Encore. It has done the job. Part of the re-design, the Resolute Acclaim added refactory package. That insulated the rear and aleviated the heat from getting at an warping out the previous plates.
I have reviewed most of the beginings of Hearth net and the dealer correspondences concerning VC. When Majestic, then CFM took over, your concerns were valid. CFM is gone, only the name sake it exist. CFM has a different owners and management today.

 

[Rob From Wisconsin]

wow, im in the loop, but not in this loop. News to me, i would love some links that explain this technology.

Here's the link to Harman & their stove &
an explanation of the technology & the advantage
of being able to "top load" as a result. Hope this
clears things up a bit.....

Rob

(broken link removed to http://www.harmanstoves.com/doc/exceptionb.pdf)

 

[Corie]

Unburned gases pass into the afterburner chamber, where
they are mixed with air and burned at very high temperatures.

I'm still not finding evidence of the smoke being passed through the coal bed as part of the design.

 

[MountainStoveGuy]

the rear baffle instead of a top baffle im aware of, thats how VC gets away with a top load on a non-cat, but like corie, what caught my eye, was the downdraft though the coal bed.

 

[Rob From Wisconsin]

Unburned gases pass into the afterburner chamber, where
they are mixed with air and burned at very high temperatures.

I'm still not finding evidence of the smoke being passed through the coal bed as part of the design.

I guess what I'm seeing here is at least the smoke is being discharged
very close to the coals, if not through them, depending on how high
your coal bed is. The closer you are to the heat source, it stands to
reason that the hotter the temp. will be, and thus you will achieve
a higher efficiency.

My 2 cents worth....

Rob

 

[fbelec]

this is old technology. i run a 1978 defiant and when the baffle is closed it shut off the smoke path directly out the top and redirects it out the bottom right hand side of the stove. so on this stove you have to build a fire up against the baffle on the right and all the smoke has to go thru the hot coals and into the secondary chamber where it meets with a new supply of oxygen for a secondary burn then back around the back of the stove up and out. it make for a five foot smoke path thru the stove for more heat extraction. if you do it right it also does not involve all the wood in the box for fire. only the wood that sits on the coals. so if done right you can get some nice long burn times.

sounds good but doesn't work unless you have the stove screamin hot.

 

[mlouwho]

I am a Harman Stove dealer. The exhaust does not go through the coals. Harman makes 2 wood stoves with a rear mounted afterburn chamber. The entrance to the chamber is low on the back of the stove, but not that low. You control when you are using this afterburn chamber with a bypass damper. If the stove is not burning hot enough, your exhaust will be going straight up. When the stove is hot, you close the damper, exhaust is now forced through the afterburner, we have cleaner, more complete combustion.

The stoves are great, work wonderfully, when properly sized for the home. I have sold many Harman stoves, all customers have been very happy. But I have also refused quite a few sales of the Harman stoves. The biggest mistake people make is buying a Harman to heat a 1000 sq ft home because "that's cool". If this stove is too big for your house, you will be building smaller fires so you are not cooked out, it will not be hot enough to use the afterburner. You will not be happy, I don't wnat you coming back to my store with complaints, so I sell these folks a different brand, smaller, more suited to their home.

 

[Rob From Wisconsin]

I am a Harman Stove dealer. The exhaust does not go through the coals. Harman makes 2 wood stoves with a rear mounted afterburn chamber. The entrance to the chamber is low on the back of the stove, but not that low. You control when you are using this afterburn chamber with a bypass damper. If the stove is not burning hot enough, your exhaust will be going straight up. When the stove is hot, you close the damper, exhaust is now forced through the afterburner, we have cleaner, more complete combustion.

The stoves are great, work wonderfully, when properly sized for the home. I have sold many Harman stoves, all customers have been very happy. But I have also refused quite a few sales of the Harman stoves. The biggest mistake people make is buying a Harman to heat a 1000 sq ft home because "that's cool". If this stove is too big for your house, you will be building smaller fires so you are not cooked out, it will not be hot enough to use the afterburner. You will not be happy, I don't wnat you coming back to my store with complaints, so I sell these folks a different brand, smaller, more suited to their home.

So do your users get a longer burn time with this unit, similar to a catalytic??
Just curious....

Rob

 

[mlouwho]

Exception I've heard 10 - 12 hours
Oakwood I've heard 9 - 11 hours

 

[billoetjen]

Hi Folks,
The idea behind the technology that's being discussed here is nothing new, as many of you have pointed out.
The manufacturers are taking it to a new generation; more refined in execution (I hope).
My Resolute Acclaim - 15 years old and going strong - works on the same principle.
After getting a fire up to 400 or so degrees stack temp, and a good draft going, I shut down the damper (located high up and at the rear of the stove). When the damper is open, the gases and flame are fed straight into the exit stove pipe. Shut the damper*, and the gases are drawn down and back, through a small opening at the base of the fire. A slope built into the grates keeps embers collected around this opening. When everything is going just right, it sounds like a furnace if you crack open the top-load lid, and the coals around the opening are literally white-hot. I'll bet it's around a thousand degrees right where the gases have to pass through.
Ideally, with the right amount of air coming in and the draft, etc right, there is almost no unburned hydrocarbons. No emissions and almost perfect efficiency.
That is ... if you don't have a chunk of wood that's rolled in front of the opening; or the temperature wasn't exactly right to start with; or you left the damper open a couple of minutes too long and now the stack thermometer is pinned at 900; or the wood wasn't properly seasoned; or the opening got blocked for some other reason; or the barometric balance wasn't just right and now there's a back-draft....
That's why I keep saying that my Acclaim is picky or "fussy."
It's great when everything is just right, I don't exaggerate when I say brush out the chimney once a season... but it took me five seasons to get used to its idiosyncracies.
I'm banking on the folks at VC taking the new downdraft technology to another level. I'll let you know this fall after I've had a chance to mess with my new Encore.
Bill

 

[mlouwho]

Great explaination Bill!

 

[fbelec]

bill question for ya

when you kick in your secondary burn or damper does you stack temp go up?
i run a old defiant with a secondary chamber. it's hard to get the secondary to go. but when it does it burns us out of the house.

 

[billoetjen]

Good question there.
I stayed at a friend's house & heated with a Defiant for awhile. Not a great design, if you ask me. Too many compromises. We couldn't get the secondary to work AT ALL. I thought it was a big creosote maker.
About the Acclaim, stack temperature drops with the damper closed. We run it at that point with the air shut way down; almost closed off.
I shudder to think of the damage it would do to keep it going at full tilt like that.
Like I said before, the Acclaim is fussy. You have to keep going back to it and checking on it every hour or so to make sure that the stack temp stays high enough. Sometimes you have to open up the air some to keep it at optimum. Rarely, you have to open up the damper again to revive it.
Great stove, just gotta think about it too much.
Bill

 

[fbelec]

yes it is a big creosote maker. the manual tells you if you burn in the damp down position then on the next fire run damper open for at least 20 minutes hot. i think they knew that it was a big creosote maker. i burn with a stack temp around 400 and that keeps the smoke down to almost nothing. what did you mean by compromises?

 

[bwolfe1]

I have a stove that uses this technology that has not been mentioned. Its a Sedore Md: 2000 and it runs using the two chamber method where the smoke and gases recirculate in the front chamber and move to the back and out stack after being reburned or burned out. This stove puts out an amaising amount of heat and burns 10-12 hours easily. It sounds like there may be a few differances between the downdraft principle but the Sedore does just that.