Slowing down an Avalon 996

[AndyGoldstein]

Folks,

I have a 12 year old Avalon 996 installed as a fireplace insert, and I've never been able to get more than a 3 hour burn time out of this puppy. It vents into the fireplace flue with a 6" liner that runs the full height - 24 feet. That's a tall stack, but that's the height of the chimney - no choice about that. 4 years ago I replaced the door gasket and installed the liner. (It used to just vent into the 12" flue.) That helped some, but lately it's more or less back to its old ways. My typical load is 3 pieces of 3-5" thick good dry ash or maple.

I went around the edges of the door with a smoky piece of kindling and didn't see any obvious air intake around the door. This unit has the old lever damper control at the bottom right, and I've always had the feeling that the damper doesn't close very well. The unit doesn't overheat, but burns brightly with a top temperature of 350-400 with the damper pushed shut. There were two 3/8" bypass holes on either side that I've already plugged. Unfortunately a flue damper isn't really an option because the entire flue is enclosed.

Any bright ideas on how I can slow this thing down a bit? The good news is it's nice and clean. (I clean the flue once a year and get out half a bucket of dry powder.)

Thanx much - Andy

 

[elkimmeg]

Andy full time between burning requires full loade not 3 splits also 350 to 400 is bearily enought heat to get real heat out of that puppy one has to take it over 500
If you can achieve 500 with a full load and damper closed you will see the burn times you are looking for do not plug secondary holes you are changing the entire dymanics of that stove
Inorder to achieve secondary burn you will need to bring the stove up to and past 500 degrees and your secondary air inlets open. dampered down. you may start out with your 3 splits get then going good get a good bed of coals glowing and add the rest to fill the firebox. cut primary air back as the fire works on the wood load don't be too quick to engage the damper 600 degrees is fine too actually on cold days we are experiencing 650 is my target temp. If you do as I said you will discover preformance you never knew that stove had.

good luck and welcome aboard Hearth.com

Ps keep us posted as you experment let us know how your stove reacts

 

[AndyGoldstein]

Elkimmeg - Thanx for the quick comeback!

So basically it sounds like I shouldn't be so wimpy in loading up the stove. Just as a point of calibration, I should explain that because this is an enclosed fireplace insert,
(1) I have the thermometer on the sloping front directly above the door, not farther back on the actual top, and
(2) I run it with a blower (necessary to get the heat out of the enclosure).
These two factors may make the thermometer read a little lower than what you'd get on a free-standing stove with no blower.

I'm a little confused about what you say about the primary and secondary air feed. By secondary air I assume you mean what's fed into the air tube across the top, right? Back when I was giving the stove a work-over, I poked a wire into the bypass holes on the sides (the ones I plugged), and as far as I could tell those holes fed into the same air path as the main damper. (That is, I was able to poke the damper with the wire through the air hole.) Is there any info available on what the air path in this stove looks like?

Anyway, here's a photo of the stove going with a full load and the damper all the way down. (It's only 4 splits but it's about as full as I can get it. There's a decent bed of ashes down; if I cleaned it out completely I could get in a little more.)

The flames don't show up on a digital damera as well as they do to the eye, but I think you can see that I'm getting plenty of secondary air. You can see the flames around the air tube on either side; in the center there's enough downwash that the flames only form half-way down the glass. So what I'm wondering is whether it should be possible to reduce the air more than this.

You can also see that the welded-on piece of the Y bar is significantly warped (the bulge under the left side of the air tube). The Y bar is 4 years old. I take that as evidence that it's getting reasonably hot in there...

Cheers - Andy

 

[webbie]

Larger splits of wood might help - when possible.
Also, you might want to slow down the secondary air - it comes in those two holes on the left and right side about 3/4 way up the stove - we used to put little metal caps in them...but you can experiment with a small piece of insulation or something.

Also check the draft control to make certain it is fairly tight and that it is closing all the way, You can bang up a bit on the angles that hold it if need be to seat it tighter against the stove bottom.

 

[AndyGoldstein]

Oh, look at that! I finally figured it out and found the secondary air inlets. As you say, they're on either side about 3/4 up the sides - about 3/4" in diameter. Looks like they line up with the ends of the secondary air tube. The holes I'd plugged that I mentioned in my initial post are down near the bottom and are bypass holes on the primary air damper.

I'll have to figure out a good way to get at the secondary inlets. It's tough from the outside because they're a couple inches inside the jacket that surrounds the firebox. They're visible through the air intake grills but pretty hard to reach. I suspect the best approach would be to take out the secondary air tube and put a reducer in each end. I feel justified in cutting down the secondary air because that 24 foot flue pulls pretty hard.

You're also right about the primary air damper being a potential problem. It's not quite as you describe, though - it doesn't slide in and out like later Avalon stoves. This is an earlier model where the damper is a plate on a rotating shaft and operates like the butterfly valve in a carburetor. The damper lever has a springy feel at the point where it should be closing, and I suspect that the plate may not be making uniform contact as it closes. Ajusting it is a fussy exercise.

Anyway, thanx a bunch for pointing me in the right direction.

Cheers - Andy