down draft tech

[brad wilton]

how does down draft tech work on stove ?

 

[Ashful]

Downdraft usually means the exhaust gasses from the firebox go downward to reach the secondary combustion system, before going up the flue. In very old days (think Russian stoves and masonry heaters), this was used to increase exhaust path length and heat extraction. Fast forward to the VC and Jotul stoves ca.1990, and it was used to fit a secondary combustion system into the stove without impacting stove height. The Jotul design worked nicely, in that they used this feature to lower exhaust gas velocity, and drop ash out of the exhaust before it turned 180 degrees to go up thru the cat combuster. I believe the Harman Firedome is probably the lead on marketing downdraft technology today, but it is not a new idea.

 

[brad wilton]

thanks joful ,so it is a system that does work if implemented properly

 

[begreen]

It seems to have worked better in older stoves This tech was used on the original VC stoves, Tempwood, etc.. and is currently still used in the Sedore all which are not EPA stoves. The strive for cleaner burning meant a hotter secondary combustion which has been the devil of many current designs. However, there is the fantastic Wittus Twin-Fire which is an exceptionally clean burner, very efficient heater and gives off a heckuva light show. Wish it weren't so expensive.

 

[Ashful]

...there is the fantastic Wittus Twin-Fire

Very sexy video, for a very ugly stove.

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[DougA]

Very sexy video, for a very ugly stove.

That's why it's so expensive. You just can't find legs like that at Walmart or Tractor Supply.

 

[FionaD]

They're actually all men.

 

[branchburner]

thanks joful ,so it is a system that does work if implemented properly

It is sensitive to draft, so the range of draft conditions in which it works well is probably narrower than for other stoves. Even when it works well, the high temps for secondary combustion can mean higher flue temps than for other burn technologies. That doesn't mean excessively high, but could mean some unwanted heat loss.

Since the stoves like to burn hot, they are better for cold weather, 24/7 burning and not as good for milder shoulder-season burning.

 

[Ashful]

It is sensitive to draft, so the range of draft conditions in which it works well is probably narrower than for other stoves. Even when it works well, the high temps for secondary combustion can mean higher flue temps than for other burn technologies. That doesn't mean excessively high, but could mean some unwanted heat loss.

Since the stoves like to burn hot, they are better for cold weather, 24/7 burning and not as good for milder shoulder-season burning.

Everything I have read indicates your statements are true, with respect to downdraft non-cat stoves. However, don't forget the Jotul and old VC downdraft designs were catalytic stoves. I have one of my Jotuls cruising at 380F stovetop right now, and the flue temp is 160F. Low enough for ya'?

 

[begreen]

The old VC downdraft stoves (Defiant, Vigilant, Resolute and Intrepid) were not catalytic. Are u sure Jotul cats were downdraft?

 

[Ashful]

I guess I'm only as sure as the forum members here who have told me my stoves are. In the Jotul Firelight 12, exhaust gas passes thru two ports in the rear burn plate, about mid-high on rear wall of firebox. Gas goes down about 3", under a "lintel" for lack of a better term, and back up thru cat combuster suspended horizontaly behind firebox.

 

[jharkin]

The old VC downdraft stoves (Defiant, Vigilant, Resolute and Intrepid) were not catalytic. Are u sure Jotul cats were downdraft?

The first generation VC stoves actually where not exactlydowndraft either. They called them "horizontal combustion" I grew up around a Resolute which my Dad still uses to this day so Ive seen it first hand.

In those old stoves when you closed the damper, the flue gases got sucked into an exhaust opening down low on the side of the firebox and then passed horizontally through a chamber in the back of the stove and up the flue. The idea was to build up a really deep coal bed and force the smoke to flow through, or at least over the hot coals on its way out, stimulating a rudimentary secondary combustion.

The Defiant Encore I think was the first true VC downdraft in the sense that the flue gasses get forced down through the catalyst after leaving the primary firebox. That and all the later designs operate downdraft in both the catalytic and non catalytic models. The cat s force the exhaust down through the catalyst, the noncats force the exhaust down through a reburn chamber with injected secondary air.


SO as to Jotul's Joful... I guess it depends on how you define "downdraft" Based on the description it seems that the flue gasses do have to go down at first, but then they are pasing up throught the cat???

 

[begreen]

Thanks for the memory jog Jeremy. You are correct, I can remember the salesperson talking about horizontal combustion when we got our Resolute, though I thought of it more as a marketing term.

 

[bwolfe1]

The Sedore 3000 is a front, or side draft stove. The secondary combustion is done in the rear compartment
Here's a link that describes this process better.

http://www.sedoreusa.com/how-it-works/