The Double Edged Stove Sword

[Troutchaser]

Many of you have been kind with your patience to my questions. I've burned wood for three weeks now.

Still working on the downdraft combustion and thought that I'd leave more primary air on her last night when shutting bypass. When I finally worked down to very minimal air and went out to check the flue (flashlight examination), I noticed vapor (smoke, water) just barely coming out from under the cap. Nothing like my neighbors heat cannon.
But, if I give her a fraction more air to speed up the flue, then I'm burning way too fast and hot. Hitting 600deg. stovetop and 1100deg. flue temps. don't seem to be a problem with this stove. This is with a deep coal bed.

I'm afraid that my flue gasses are crawling out and cooling too much in the process. But more air into the stove is burning the wood up quick. Has anyone quarreled with this before?

 

[brokeburner]

Man you have to remember you are burning wood in order to get some kind of overnight burn you have to sacrifice some smoke rolling up the chimney some of the white vapor could be steam . just burn hot in the morning to burn some of that crap off .

 

[karri0n]

1100 degree flue is hot, especially on a 600 degree stovetop. You're losing a lot of heat up the flue.

Can we have a bit more info about your setup?

How tall is your chimney?

Is the chimney interior or exterior, or is this a lined masonry chimney?

If this is a masonry chimney, is it lined all the way to the top?

How long has your wood been split and stacked? (if you buy your wood, how long have you PERSONALLY seen it being split and stacked for, regardless of when the wood guy says it was split)

Do you have a damper in the pipe?

 

[Troutchaser]

I have 21 feet of flue. 9 feet DW in the house. I have no flue damper. I generally just open/close the bypass damper as needed.

Wood was purchased a couple of months ago. I've split it down smaller to help in drying some of the splits. The stuff was barn kept and seems pretty dry already, but I haven't checked it. I'd say it aint bad, but could be better.

Just this morning I started up some kindling (pallet wood) and two small splits on a fair bed of coals. In ten minutes the flue was 1000 deg. and stove top was only 200 ( I walked off to prep. for work). I closed the bypass about 80% and backed the air down to maybe 25% and everything reversed order-flue 600 deg. and stove top 600deg within half hour. This is just a typical morning burn hot and cool down before everyone leaves for school and work. Is this abnormal?

Also, certainly others here burn their EPA stoves without going nuclear all the time. Since I'm still learning the aspects of the downdraft, I'm doing a lot of smaller "traditional" burns. I'd love to see SOP for anyone else doing this.

Thanks again all for your help.

 

[karri0n]

I can't say with certainty, as I've never operated a downdraft stove, but the key to high efficiency and good burn in most EPA stoves is to load her up to the gills, let the burn get well established, close the bypass, then start lowering the air control until fully or mostly closed. If you're burning "smaller" fires, it's possible you aren't heating the firebox enough for the downdraft combustor to burn off all the gases.

If you are dealing with less than optimal wood, more time with higher air settings will be required to get the wood dry enough to burn well.

As far as your wood, do you hear any sizzling if you open the door 15 minutes into a burn? If your wood is sizzling, then you can be certain it's as simple as not-so-great wood. If you bought your wood two months ago, I'd say there's a very good possibility of the stuff not being seasoned enough.

I'm not sure how to tell, with a downdraft unit, whether or not you are getting full secondary combustion before closing the air down all the way. On a stove where the air is introduced below a baffle, it's fairly easy to tell by looking to the top of the firebox to see if there is flame, and on a catalytic unit, you can usually see the cat glowing. The downdrafft re-burn chamber would normally be hidden from view by both the fuel charge and the fact that it's a contained unit, so it could be difficult to determine if your secondary combustion is kicking in fully.

Hopefully someone who has this stove or a similar downdraft unit can chime in with the particulars of operating a downdraft unit.

 

[Troutchaser]

Ya, we've kicked around this downdraft technology quite a bit. It's tricky, but just last night I had it working nicely . The only way I know to tell is by the flue emissions. Clear tells me it's working. Lots of times there is a faint trail of something-smoke and/or steam.

I've watched Gordo's videos and have tried his techniques. So far so good there. Still learning. I'm thinking the trick might be to send that heat through the combuster box instead of up the flue to get it spanking hot. And I have noticed that Gordo seems to do the same thing when closing the bypass. Leave the air on fully and warm up the combuster. Stovetop temps. do get up there with the bypass closed and air wide open though. But here's another question and one I'm experimenting with. Can I run full air through the combuster before it's up to temp. and not make smoke? What would be the difference between that and straight up the flue?

I have never had sizzling wood in this stove. Absolutely not. Maybe too moist, but far from sizzling-and I've watched. When I throw splits on a coal bed they usually light while I'm still trying to fill the box. And with those high stove and flue temps., can I assume that my wood is pretty decent? My darling wife discovered my den was full of dehumidified cherry yesterday. She wasn't impressed.

We bought the Leyden for its look and not its ease of operation. I'll get it eventually-I hope. Thanks for any time you can give thinking about this.

 

[karri0n]

I'd say it's definitely a good idea to keep the air control open after closing the bypass for at least a few minutes. When the heat is going straight up and out, there's no reason for the downdraft combustor to have gotten up to secondary burn temps. the gases just won't be flowing that way yet. I didn't mean it to sound like you should close the primary at the same time as engaging the downdraft combustor.

 

[Troutchaser]

That might be the ticket then. I wonder now what temp. my probe should read when the combuster is up to temp. and ready for backing off the air? I'm thinking the combuster needs 1100deg. or better to work. What would that translate to 18" up the flue? See what I mean? That will be the trick-correlating those two. I think it worked at about 850 on the probe last night. Took a while to get there though while drawing only through the combuster.

 

[karri0n]

Ideally, stovetop temps will be higher than flue temps. This might not be possible with your stove, though, since the secondary combustion happens at the back, while on a burn-tube style stove or some cat stoves, the combustion happens right under the stovetop.

I'm still hoping for someone with a lopi or similar style downdraft stove to chime in. I know these can be somewhat of a different animal.